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How it works
In flight the game has one sun, and one "ambient" colour for whatever the sun does not reach: a flat grey, the same from every direction. It is 0.24 (of full brightness, as shown) in air and 0.06 in a vacuum, by night as by day. Nothing else gives light: not the sky, not the ground, not an engine's flame.
Two things the game's shaders can do are never used by it, and this mod is built on them:
- They take ambient light that differs with direction (it was tried: with blue set from one side and red from the other, a rocket takes the two colours on its two sides).
- They take lamps of a cheap kind, worked out at the corners of what they light instead of at every dot of it, four at a time for each thing drawn, at no cost worth the name. On the pad at night such a lamp is hard to tell from the costly kind.
Every frame, for the place the craft being flown is at, the light arriving from every direction is added up into what Unity calls an ambient probe (nine numbers a colour) and given to the two cameras that draw the scene the craft is in. Into it go:
- The sky, where the craft is in air: partly from straight up and partly from all round the horizon, so that an upright wall gets three fifths of what level ground gets, and what faces down gets little. Its colour is worked out from the three wavelengths the game itself draws that planet's sky from: air scatters short waves more than long ones, by the fourth power, and what it scatters is what lights the shade. So shade on Kerbin is faintly blue, on Duna faintly rust. It is as strong as the air is thick and the sun is high: on level ground at noon as bright as the game's flat light was on everything, half that with the sun at sixteen degrees, and fading through twilight until the sun is thirteen degrees under.
- The sky's warm side. With the sun low, the sky on the sun's side is lit by light that has come a long way through the air and lost its blue; it goes on glowing for a while after the sun has gone.
- The ground, from straight down and from a little below level all round: in the ground's own colour (below), as bright as the sun is on that ground and in the colour the sunlight has by then, and filling as much of the view below as the planet does from that height. From orbit a body with air is brighter than its ground: the air and clouds add about a sixth of the sunlight on their own account.
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Every other world in the sky, from its own direction, in the mean colour of its picture: by how much
of the sky it takes up, how much of its lit side is turned this way, and how strong the sun is out
there. From Kerbin the full Mun gives a fifty-thousandth of daylight. That is nothing on a screen, so
when the sun is gone and the sky is dark the light is turned up as an eye turns itself up, far enough
that a full Mun lights what faces it about as well as the game's flat light did, and it turns cold and
silver, because an eye in the dark sees blue best. Jool over Laythe needs no such help. The brightest of
them is handed to every shader (
_NaturalLightWorld: which way it is;_NaturalLightWorldLight: its light as turned up here), and the readout says where it stands ("the Mun's light 0.26, 24° up, bearing 270°"). The Natural Ocean mod lays the Mun's path on the sea from it, as glittering as the sun's. - The least there ever is, from everywhere, so that a night side is dark and not black.
The planets seen from afar are drawn by another camera and keep the game's own light; the insides of cockpits and the crew's portraits have light of their own (see "Inside the craft").
The game's sun is white and of one strength whatever it shines through. Three things are done to it.
- Its colour through the air. Where Scatterer is installed and set to dim and redden a low sun, that is left to Scatterer. Where nothing does it, this mod does: by how much air the sunlight has come through (Kasten and Young's rule for a low sun), taking out most what the sky is the colour of.
- The eye keeps pace. A sun dimmed by the air leaves a scene that is simply darker, and on a screen that reads as murk. A camera, or an eye, opens up instead. So the sun is turned back up by most of what the air took from it (by how bright the remainder looks, held back so that an evening sun's red is never pushed past full), and the sky with it. To know how much Scatterer took, the cameras are asked at the moment of drawing what colour they find the sun to be, against what it was set to.
- Its shadows. The game lets a quarter of the sunlight through every shadow. With real light in the shade that is not needed, and the shadows are made complete.
- What the clouds leave of it (with a weather mod; see weather). Since 0.10.0 given as the sun's strength, at the moment the scene's cameras draw, and given back for every other camera; not as its colour. Scatterer, where it dims and reddens a low sun itself, puts a colour of its own on the sun just before those cameras draw, one it kept from when the scene began: set to black under an overcast, the sun was found at (1.15, 0.86, 0.46) as the cameras drew, and shone through any overcast at full strength (0.9.0's cloud light did nothing to the sun wherever Scatterer was installed). The game sets the strength afresh every frame, so it is taken as the game left it, once a frame.
A flame is long and wide, and one lamp is a point: a lamp under a rocket lights the pad and, at a grazing angle, next to nothing of the rocket. What lights the sides of a real rocket at night is the width of its flame and, far more, the ground under it, lit white-hot and throwing that back up from all round. So each flame is made of:
- one lamp of the costly kind where it leaves the engine (the engine's bell, the pad, the highlights);
- three of the cheap kind round the flame, a third of the way down it and as far out as it is wide;
- three more round the place where the flame meets the ground, when it does: the ground's own glow, which fades as the craft climbs out of reach.
Brightness goes by thrust and by what is burnt (solid fuel burns brightest, a jet dimmest), colour by the propellant: orange for fuel and oxidiser, near white for solid fuel, blue for xenon. Engines within six metres of one another share a flame, there are never more than three flames, and all of it flickers.
(The weather's own drops, flakes and blowing dust, Natural Weather's, light themselves by the scene's light as they are drawn: their materials are named "NaturalWeather..." and left alone here. Taken for smoke, they read dark in any light.)
The game draws its smoke in one brightness whatever light falls on it: an engine's trail and the cloud at a launch are as white at midnight as at noon, which among dark ground and a rocket lit only by its own flame looks pasted on. The game's smoke shaders have a tint, and the mod sets it, for each source of smoke, by the light where that source is: the sun as it reaches the craft (gold at sunrise, nothing at night), the sky and the ground from all round, a flame by how near it is, and a launch site's floodlights. Full day leaves the smoke exactly as the game has it; a flame or a lamp shows on it by as much as the day has gone. The tint is set for each drawing and not in the game's materials, so nothing is left changed when the mod is switched off.
It is found by its shader: the game's own particle shaders that draw over what is behind them (flames and sparks are added to what is behind them, and are their own light). Twice a second the scene is looked through for new ones.
Every place a craft can be rolled out to (the pad, the runway's ends, the island airfield, and the other sites the game and its expansions have) gets four floodlights round it, and one weak wide light above the middle for what four lamps do to damp night air. They come on one after another as the sun reaches the horizon, and go out at dawn. Only sites within three and a half kilometres of the craft have them.
The searchlights. Asked for as: "with the spotlights, have it actually have spotlight models". Each floodlight is a thing that stands there, by day as well as by night: a xenon searchlight of the kind that lit the Apollo and Shuttle pads (banks of them, twenty kilowatts each): a round projector head a metre across of grey-painted cast aluminium, with its front glass, the faceted reflector and the short-arc lamp seen behind the glass, cooling fins round its back and handles to aim it by; on a yoke over a pan bearing, with a hand wheel to lock its tilt; on a square steel post with the lamp's ballast box on its back (louvres, a rating plate, a high-voltage sign without words) and its cable up the post to the yoke; bolted to a concrete footing. The top of the head is about three metres up when it is turned up at a rocket. (The model is made with a head 0.8 metres across and drawn a quarter as big again: a big unit of its kind, and one that can be made out from where the game's camera usually is.)
It is made in Blender by a script kept with the mod (Model/floodlight.py: nothing downloaded, no model file
kept by hand), which bakes the shading of its folds (ambient occlusion), its dust and the gloss of each part
into one picture, and the fine relief (the casting's grain, the louvres, the concrete's pores) into a normal map,
and writes its meshes in a small file of the mod's own (floodlight.mesh; the same layout as On Foot's tug's,
read by Natural Light's own reader). It is drawn with the game's own part shaders, so the sun, the sky, the
ground and every lamp light it as they light everything else, and it throws a shadow (by day: there is no sun's
shadow to throw by night). About 12,000 triangles (5,500 for the post, 6,500 for the head). A site's four bodies
are joined into one mesh where they stand and drawn at once; what glows in each head (the reflector, the lamp,
the glass) is drawn apart, a mesh for each head, so that each lamp strikes on its own. All of it is in one
frame, the site's, and drawn from one place (see "One frame" below). They have no colliders: nothing a craft could
hit, wherever some other mod's site puts them. Measured by night on the pad with the frame-rate cap lifted,
with the twelve round the pad and the runway near: about half a thousandth of a second a frame of 20 (0.2 to
0.9 in nine measurements, drawn and not drawn in turn); joining the bodies and leaving out their shadows by
night did not bring that down by as much as the measurement can tell.
(The game's emissive shader reads its glow's picture through a mesh's second set of coordinates, it seems: the reflector, whose glow is its own picture, did not glow at all until its mesh was given the same coordinates twice, while the lamp, whose glow is a flat white, did.)
The post is turned to face the site and the head tilted up on its yoke to point where the beam goes. The light comes out of the glass: a lamp of the cheap kind a metre in front of it (so that it lights what it points at and not its own head), the beam from the glass itself, and the reflector and the lamp glowing behind the glass when it is lit. Its glare (a soft disc turned to the camera, so that a lamp far off is a point of light) is seen only from in front: from the side the glass glows and no more, and from behind there is none.
One frame for a site's searchlights (0.10.3). Said of 0.10.2: "the glass part is slightly shifted
downward outside of its holding place". The model was right (in floodlight.mesh the glass's middle is on
the head's axis to a hundredth of a millimetre); the drawing was not. The space centre hangs from a point on
its planet 600 km from the planet's middle, and the game keeps places as 32-bit numbers, which are no finer
than a few centimetres that far out. So what the game says of a thing's place there does not add up. Measured
on the pad (2026-10-10): a frame's way into the world and its way back out (its two matrices) were 12.5 cm
apart, nearly all of it up and down, and a head's place and its post's, each worked out on its own, 3 to 9 cm.
Since the bodies were joined (0.10.1) a searchlight was drawn from two places, the joined bodies from the
site's and each head's glowing parts from the head's own, and where each body went into the joined mesh was
worked out through both of the site's matrices. The bodies went in 15 cm and more too high, and the glass, the
reflector and the lamp hung 12.5 cm below their housing on all four, with the sky showing through the bezel
above them. (It differs from one load of the game to the next, though not with a time warp within one: in
0.10.1's own pictures it is some 10 cm by day and nearly nothing that night.) Now every piece of a site's
four is in the site's frame, put there by the model's own small numbers (the head in its post, the post in
the site), and all of it is drawn from the site's one place: wherever the world's numbers put that place, the
pieces go together. Measured after: 0.0 mm between each lamp and its housing and between each head and its
yoke, on the pad by day and by night and beside the runway. (The lamp's glare and its beam are still drawn
from a place of their own at the glass: soft things, on which some centimetres do not show. And a whole
searchlight can still stand some centimetres higher or lower on the ground than it was put, as the game's own
buildings do. Its footing, drawn 15 cm too high with the rest until now, is the low slab it was modelled as.)
Where they stand. The four of a site are placed together, so that they stand alike. Round a pad: at the corners of one square about where the craft stands, on the compass's diagonals, each the same distance out: twenty metres if all four can stand there, else the widest square, down to twelve metres out, whose four corners will all do (if none on the diagonals will, a square turned fifteen, thirty or forty-five degrees from them); all turned up at about the height of a rocket's shoulder. On the space centre's pad that is twelve metres, at the corners of the square painted round its grate (thirteen is too near the edge of its top). Round a runway they must not stand on it. A site is taken to be a runway when its own surface (whatever is part of the site, round where the craft stands, found by casting rays down at it every four metres out in 36 directions) reaches 200 metres or more one way and is at most 120 metres across and a third as wide as it is long: the space centre's runway, the island airfield, the desert's. Beside a runway they stand off its surface, two each side, fourteen metres either way along it from where the craft stands, turned in across it a little above the craft, each side's two the same distance out from its edge: four metres, or as much further (by twos, up to twelve more) as lets all four stand. A spot will not do where the ground is not level, or not level for three and a half metres all round (so at an edge); much higher or lower than where the craft stands (on a roof, in a pit); on the runway's own surface; or where something stands in the way of the post, the yoke or the head. Only where no such square or rows can be found is each lamp placed on its own, at the nearest spot round its place that will do, out to twelve metres. (The edge rule is for the space centre's pad, whose colliders reach a little past its shape at its corners: there a searchlight first stood in the air over the pad's sloping side.)
(Until 0.10.3 every lamp was placed on its own. The top of the space centre's pad is too small for twenty metres out, and its four came to stand at three distances from the rocket: the two eastern ones 12 metres out, by the corners of the grate, and the two western ones four metres aside on the pad's shoulders, 17 and 20 metres out. Said of it: "the front two spotlights ... especially the one in the bottom right, it is shifted outward for some reason". And the way a runway runs was taken to be the first of the ways its surface reaches furthest, which at the space centre's wide runway is ten degrees off the way it does run: its four stood askew to it, one side's pair some twenty metres further along than the other's. It is now the middle of those ways, found to a degree (91 for that runway's 90), and its four stand square to it, 64 metres either side of the craft and 14 either way along.)
Each lamp has a beam that shows in the air: a strip 150 metres long from the glass up over the middle of the site, turned about its own length to face the camera, 0.85 metres wide at the glass and 30 at its end, drawn as added light with one of the game's own particle shaders. (A strip that widens cannot be two triangles, or the picture on it is skewed: it is cut into fourteen lengths with a row of corners down its middle.)
The runway at the space centre has two rows of edge lamps, fifty-two a side and forty-seven metres apart, and a big lamp at each of its four corners. The game draws them as glowing paint on meshes of their own and switches them on at dusk, and they light nothing: rows of bright spots on black concrete. A real runway's edge lamps throw light on the concrete and the grass round each one, and an aircraft rolling down the runway is lit by each in turn as it passes.
There is no list of the lamps anywhere in the game. They are found from what draws them: each triangle of a lamp mesh is looked up in the picture that says where it glows, and every bright part of it is taken back to where it is on the triangle; bright parts within a few metres of one another are one lamp. (The same way finds the windows, below.) Each lamp then gets:
- Its pool of light on the ground: a soft patch laid on the concrete and the grass round it, a little longer along the runway than across it, brightest at the lamp and fading out over fifteen metres, the corner lamps' larger. It is drawn as added light with one of the game's own particle shaders, as the assembly building's own pools of light on its floor are: the runway is a few great flat pieces with corners hundreds of metres apart, which a lamp of the cheap kind cannot light, and there cannot be a hundred of the costly kind. The patch follows the ground under it, and fades out where it would climb onto something.
- A faint glow round the lamp itself, turned to whichever camera is drawing, a little larger the further off it is, so that the far end of a row still reads as lamps.
- For what is on the runway: at the few lamps nearest the craft being flown, real lamps of the cheap kind, which light the craft and kerbals (not the ground, which has its pools) as they pass.
All of it hangs under the game's own lamp meshes, so it goes wherever they go and is hidden whenever they are, and it comes on with the game's own switch for its lamps at dusk, faded in over a moment.
Light is half of how a scene looks; the other half is what the camera makes of it. The game makes nothing of it: what comes out brighter than white is cut off flat, so a flame, a floodlit rocket and a sunlit cloud are the same blank white. A camera, and the films and games admired for how they look, do a few things to the finished picture:
- a film curve: the bright end rolls over a shoulder instead of being cut off, so a flame or a sunlit cloud keeps its shape, and the dark end has a toe;
- contrast: light and shade, a little more than the game's;
- a glow round whatever is brighter than white;
- creases darkened, and the places where one thing meets another;
- an exposure that follows the view, as an eye does;
- a lens's darker corners and a trace of colour fringing.
Colour is left as the light makes it. The look was first asked for as "like THE FINALS" and made with stronger colour, warm lights and cold shadows, and Unity's ACES curve. Of that the user said: "way too saturated... I still want it to look like real life, but I want it to look cinematic and beautiful, not over saturated." Measured on the same views loaded afresh (0.9.0), that look added about a third to the colour of a picture by day, with a few pixels in every hundred at full strength, turned white paint a little orange, and made a night scene blue-black (the cold of the shadows was done by Unity as a colour added to every pixel); the light itself, the sky's and the ground's, added nothing that could be measured. Since 0.9.0 the curve is Unity's "Neutral" one, which brings the bright end back with little change to the hue or the strength of a colour (where ACES strengthens bright colours and turns their hue); the contrast is stronger, the colour a hair over the picture's own (first left exactly as it was; the user then asked for it "just oh so very slightly more up... and then the contrast a touch up too"), there is no cold in the shadows and only a trace of warmth in the lights. The Neutral curve leaves the middle of the picture as bright as it is, where ACES darkened it (and the light had been turned up to make up for that: see below), so the exposure is set a third of a stop under what it was, and the picture is as bright as before. (Colour taken a touch under the picture's own, to make up for the contrast, which strengthens it a little, was tried: the space centre and a sunset came out grey.) "Contrast and colour" above 1 adds colour back for a player who wants it.
Measured the same way, on six views (the pad by day, a launch, sunset, the space centre, the pad by night under the floodlights, orbit), the colour now comes out as strong as in the game's own picture by day and by night and a little under it at sunset: a tenth to a quarter less than the old look, and by night two thirds less. No pixel is at full strength, where the old look had three in every hundred by day; white paint is white; and the night is black, not blue.
(AgX, the film curve Blender has used since 4.0, on which a bright colour goes to white as it brightens, was made as a lookup for Unity's grading and tried. It measured the same as the Neutral curve on these views, and Unity's grading takes no exposure with a lookup of one's own: the camera's eye, which is an exposure, would have stopped working. So it is not used.)
None of it needs anything new drawn: it is arithmetic on the picture, and Unity's own post-processing
does all of it. The game does not ship that, but the TUFX mod brings it, for every system the game runs
on. So the mod asks Keystone's film for a grade every frame, and Keystone hands it to TUFX as a layer of
settings over whatever TUFX profile is in use (see Keystone's Film). The profile must keep more than
white in the picture ("hdr", which TUFX's own profiles have): without it there is nothing brighter than
white left to roll over or to glow, and the page says so.
(Shown by day: by night the film look's dark end is deep, and it is the camera's eye, opening up, that makes a night scene readable; with the eye held still for a fair comparison, a night picture with the film look on is simply darker than one without it.)
The light is turned up to match. Until now the sky and the ground could light the shade no more brightly than the game's flat grey did, because anything more ran into white and was cut off. With a film curve to roll the bright end over, that no longer holds: where the film look is at work the sky fills the shade half as brightly again, the ground seven tenths more, and the sun is a fifth stronger. That, more than the curve itself, is what makes a white rocket white at midday.
The camera's eye. Asked for as: "when there is less light you can see more and when there is a lot the background is very dark, like real life". Unity's own eye needs a kind of shader the game's OpenGL on a Mac has not got, so the brightness of the view is measured by the mod: before anything else is done to the picture it is shrunk, in steps of a half, to a few thousand dots (80 by 45), and those are read back a few times a second. Three things are taken from them: how bright the whole view is, black sky and all; how bright what is in it is, the black left out; and how bright its brightest three-hundredth is.
- In the dark the eye opens, by six tenths of how dark the whole view is, up to a little over three stops (nine times the light): slowly, about half a stop a second, so that coming out of the light it is some seconds before the dark shows anything.
- But no further than the brightest thing in view can bear. With a floodlit rocket in sight, or a sunlit one against black space, the eye stays shut and everything else stays as dark as it is. (The share is so small because what matters is whether anything bright is in sight at all: a rocket seen from across the pad is a few of those dots.)
- In the light it closes, fast: by two thirds of how bright the view is, and further for a view full of something much brighter than white, a flame from close to: all the way (two and a half stops) where a twenty-fifth of the view or more is that bright, and by less for less. (It used to shut all the way for a flame of any size, and a launch seen from across the pad at dawn put the dawn out.) Not for the sun itself, though, nor for the glare close round it (an eighth of the picture's height): the sun burns out in every picture ever taken of it, and the exposure is set by the sky round it. And by day hardly at all for a flame (since 0.7.1): six tenths of a stop at the most. Nobody stops a camera down for a rocket's flame in daylight; the flame burns out white and the day stays as it is. Until then a launch watched from thirty metres turned the afternoon to night as the engines lit. Whether it is day is told by the middle one of the view's dots, were they put in order of brightness, and not by their mean, which the flame is part of.
- The stars are dimmed by how bright the brightest thing in view is, and come out again in the dark. The game draws them at one brightness whatever else is in view; an eye set for a sunlit planet sees none.
- A picture pushed open is given a faint grain, as film pushed that far has, which also hides the steps that show when what little light there was is multiplied up.
Where this eye is at work the mod's older way of seeing by moonlight (turning the Mun's light itself up) does only a fifth of what it did, and leaves the rest to the eye, which does it for the whole picture and knows when it must stay shut.
Pixels that are not numbers. Some of the game's own shaders give a pixel here and there that is not a number at all: a highlight that comes out as nothing divided by nothing. The water tower by the launch pad, seen against a low sun, has a line of them down each strut. In the game as it comes they are stored as black and never seen. In a picture that keeps more than white, which a film look has to have, they are still there when the picture is developed, and three things go wrong. Each comes out as a bright yellow or green dot. The smoothing of edges over time keeps a little of every past picture, and keeps such a pixel for good: the dot stays where it was on the screen when the camera turns, so that a turn of the camera left dotted lines hanging in the sky. And the eye, measuring the view, took each as the brightest thing there could be: a dozen of them shut it two and a half stops, and a sunrise seen from the pad was nearly black. That last was found first, and was the worst.
Unity's post-processing has a cure, which TUFX has switched on, and which does nothing in the game's OpenGL: the test it uses is one that the graphics card's compiler takes out as never true. So the mod has its own. The shrinking of the picture for the eye is the finder: in the first halving, one such pixel spoils the whole dot it falls in. A small shader of the mod's own then draws black over the two-by-two pixels of every spoilt dot, and touches nothing else; it looks at what the number is made of, not at what it compares as, so no compiler can take the test out. The eye leaves spoilt dots out of its sums, and what the smoothing had kept is thrown away once, when the blacking out begins. Its cost could not be measured. (On Direct3D the same shader is built for it; where the mod's shaders cannot be used at all, Unity's own cure is expected to work, and the eye leaves such dots out all the same. On Windows with TUFX, 2026-10-10, the shader built for Direct3D was loaded and in use.)
Reading a picture back makes the game wait for the graphics card to catch up: asked for in the middle of a frame, as it first was, that cost a hitch of about twelve thousandths of a second eight times a second. It is now asked for in a way that does not wait where the card can do that, and otherwise at the very start of a frame, three times a second, which costs nothing that could be measured.
In the editors the same look is applied at one exposure, with nothing measured and nothing following the view, so that a craft looks in the assembly building as it will on the pad.
The glow begins at what shows as white (2026-10-18). Unity works the glow out from the light before the eye's exposure is put on it, and the threshold was a fixed 1.0: it began at white only with the eye as by day. At night, with the eye opened some three stops, lamps and fires that showed white had no glow, and anything far brighter than white threw a halo whatever the eye did. Now the threshold is two to the power of minus the exposure: about 1.2 by day (a little less glow), about 0.15 at night. Seen at night at the pad with a fuel crash beside it: the young fireball's core blooms as a camera's would, the flames brighter against darker smoke.
The game draws shadows in four bands of fineness by distance from the camera, out to five kilometres; the finest is the first 250 metres. On Direct3D it draws that band in to 50 metres when the camera is close to the craft, and to 100 from further off. Its own code says "if Direct3D 11" and does nothing otherwise, so a Mac or a Linux machine never gets it. The mod does the same there, with the game's own numbers: the shadow of a rocket's core on the booster beside it, which the wide band loses altogether, is then there and clean. It is left alone where Scatterer is set to handle shadows itself.
All of it works at the space centre as in flight (the light is worked out for the centre itself): the launch pad is an island of light at night with its beams over it. Two things differ, because the buildings have to be found to be clicked on: the least light is twice what it is in flight, and bright things in view hold the eye back much less.
Air with anything in it, haze, dust, spray, shows the sun's light as it passes; and where something stands in the sun's way the air behind it is dark, so the light comes round a rocket or through the struts of a tower in shafts. Asked for with the words "super cinematic and godlike".
They are made from the picture itself, by a shader of the mod's own, before the film look does anything (which then rolls them over its shoulder and gives them their glow):
- What is bright and far. The sky round the sun, as bright as it is in the picture, most of it from close round the sun itself; and black wherever something near stands in front (the game says how far off each pixel is). At half the picture's size, so that a thin strut is not missed.
- Drawn out. Each pixel gathers what lies between it and the sun, less the further off. So every bright patch is smeared outward from the sun, and everything in front of the sun throws a dark streak the same way. Twice over, the second time reaching further, at a quarter of the picture's size.
- Added to the picture, in the colour of the sunlight as it reaches the craft; and less over what is near, which has little of the lit air in front of it. The light comes round a rocket: it does not lie on it like a veil.
They are strongest with the sun low, when its light comes the long way through the air (three and a half times what they are with the sun high), fade with the air (there are none in space), and are only there with the sun in front of the camera, in the picture or just outside it. They do not need TUFX: tried with its effects switched off on the game's cameras and the picture cut off at white, they are there, only paler, since nothing then rolls them over or makes them glow.
(They show only with a low sun in front of the camera, at sunrise and sunset, which is why they are easily never seen: by day, with the sun high or behind, there are none.)
The shader is packed for the game's OpenGL, without the Unity editor (see building), which is what the game runs on a Mac and on Linux, and built for Direct3D, which it runs on Windows. Seen there on 2026-10-10 (Windows 11, an NVIDIA GeForce RTX 4080 SUPER, without TUFX): the sun three degrees up behind a rocket on the pad, its light round the rocket in shafts and the rocket's shadow streaming up from its nose, the right way up; and the same with the game started on OpenGL.
With a weather mod installed (Natural Weather; anything that answers Keystone's Weather), the light and the
air follow the weather where the craft is.
The light under cloud. What a cloud takes from the sun is not lost: most of it comes down through the cloud, spread over the whole sky, and the ground is lit from all of it and from no one side. The weather says how much of the sun's direct light gets through and the share of the light the cloud lets through (spread over the sky); a clear day's light on level ground is worked out as the game shows it (the sky's and the sun's, which the game adds as shown values) and turned into light; the cloud's share of that comes from the sky, and the sun gives only what gets through. Measured on the pad at noon, the sun 63 degrees up: a clear day 1.43 (as light, white level ground); under an overcast 0.32, 22% of it; in rain 0.11, 8%. On real days an overcast leaves a tenth to a quarter of a clear day's light and a raincloud a twentieth to a tenth. (0.9.0 had guessed the sun's share of a clear day's light a good deal too small, and had the sky alone dimmed: from above, 0.40 under an overcast against 0.66 now, 0.24 in rain against 0.41, as shown values. With Scatterer installed that was hidden by the sun shining through regardless, above; without it, the scene went night-dark.) The ground under cloud throws back what the clouds let through, in the colour the sunlight has.
The eye opens for it. A camera's meter opens two or three stops under an overcast, whatever the sky in view, and the sky burns out white in every photograph taken under one; so does the eye here (see the film look), by six tenths of the stops the weather takes from the light on level ground: under the overcast above 2.2 stops are lost and the eye opens 1.3; in the rain 3.7 and 2.2. Level ground then shows about half a clear day's light under the overcast and a third in the rain; in pictures of the pad at noon, where much is upright or, on a sunny day, in shadow, overcast and rain came out about as bright as sunshine (0.43 and 0.40 against 0.40, shown values), the sky white and nothing throwing a shadow: flat, not dark, as a camera's meter makes them. (At three quarters, tried first, the overcast pad came out a sixth brighter than the sunny one.)
Dust storms light the scene in the dust's own colour: sunlight scattered over and over through dust that was raised from the ground, so the ground's colour, paler and warmed (dust takes blue light before the rest). Duna's rust-red ground gives an ochre light, as the light under a Martian dust storm is butterscotch. On Duna in a storm at its height, the sun 39 degrees up: 40% of a clear day's light, all of it from the sky.
The veil. Beyond a few tens of metres a raindrop or a snowflake is too small to be seen as one (the weather
mod draws those near the camera), but all of them together take the light from what is behind them and put
their own in its place. So the picture is veiled by as much weather as lies between the camera and each pixel,
by a shader of the mod's own (Veil.cs, tools/shaderpack/veil.glsl):
-
How thick: from how far the weather says one can see (
WeatherHere.Seeing, the distance at which a dark thing is lost against the sky: the air takes 3.912 over it, Koschmieder's rule), less what the air takes on a clear day (thirty kilometres to lose a hill in), which the game and Scatterer draw already. - How high: as thick as that up to the weather's top (a rain's or a snowfall's cloud base, a fog's top, a dust storm's) and thinning out above, worked out exactly along each line of sight rather than stepped. So, looking up through rain, the cloud base is greyed by the rain below it and no more; from above, a fog bank lies on the ground; from far above the weather's top there is none (the clouds are another mod's).
- How far: per pixel, from the game's depth picture; where nothing was drawn it is the sky, taken as far as the weather goes up. Drawn on the far camera (beyond 400 metres) when it has drawn everything, the sky included; on the near camera when it has drawn what is solid and before what is see-through, so that the drops by the camera, flames and smoke are not veiled as if they were as far off as the ground behind them.
- Its light: the light from all round as the mod has it (the sky's and the ground's), a little more for snow than for rain (a flake throws light back every way, a drop sends most of it on forward); in the dust's colour for dust; and brighter towards the sun where the sun is out (a Henyey-Greenstein lobe, the sun's own colour), since drops, flakes and dust all throw light forward.
In rain the far side of the pad greys out and the sky under a low cloud base is grey; in snow everything whitens into the distance; in fog nothing shows past a hundred metres or so; in a dust storm on Duna the nearest hills are gone into an ochre murk. Measured from the weather at the pad: steady rain 1.8 km of seeing, snow 0.9 km, a Duna storm at its height 0.5 km.
The shader is packed for the game's OpenGL (a Mac, Linux) and built for Direct3D, like the shafts'. Seen on Windows (Direct3D, 2026-10-10) with Natural Weather holding rain, fog and snow: seeing 1.8 km, 150 m and 900 m, the far side of the pad grey, the ground lost in fog, the distance white in snow.
The veil on a round world, and lit from above (2026-10-18). The veil took the weather as flat (a line's height grew by the same amount each metre) and haze thinned over 800 m above its top: from 2 km up in haze, a level line was veiled 98.5 %, a grey bar from just over level downwards with the clouds behind it (the owner's grey band at cloud height). Now a line's height is worked out on the round world (its climb, plus its run squared over twice the world's radius), where it enters and leaves the weather is solved exactly, and haze thins over 150 m: from 2 km, 2 % at two degrees up, 7 % level, 24 % a degree down, 87 % two down, the haze a band along the horizon as from a real aircraft. And from over the top of fog, dust or haze the veil adds the sunlight the layer throws back up (by the clouds' own two-stream rule, from the layer's depth through it, times the sun's height): sea fog 123 m deep seen from 1.7 km was a flat dark grey plane, and is a lit white-grey one. (The rendering chat's veil-round and veil-lit-top.)
The game takes the sun away behind the world a craft is at (its horizon, with a little fade), and behind nothing else. But the Mun goes round Kerbin in the plane of Kerbin's own orbit: every month it passes before the sun for somewhere on Kerbin, and every month Kerbin's shadow sweeps over the Mun and every craft near it. Until 0.12.0 a craft at the Mun in Kerbin's shadow sat in full sunlight, and Kerbin under the Mun's.
So every frame, for every world but the sun and the one the craft is at, the mod works out how much of the sun's disc it covers, seen from the craft: two discs in the sky, each as wide as its radius over its distance, and the share of the sun's that the two have in common. The sun's light, and the sky's (which is the sun's, scattered), are that much dimmer. Seen from Kerbin's ground the Mun is nine tenths as wide as the sun, so its eclipses there are ring-shaped: at most some 83% of the sun covered. Seen from the Mun, Kerbin is two and a half times as wide as the sun and hides it wholly.
A world with air lets a little light round its edge, bent in through its sunsets and as red as they are: from inside Kerbin's shadow its rim glows copper (about a ten-thousandth of the sunlight), which is why the Moon in a lunar eclipse is red. A world without air leaves black. The sun's edge is taken as bright as its middle. Sixteen worlds looked at: a few microseconds a frame.
Seen on the pad at noon with the sun held 90% and wholly covered: the ground and the craft dim as they should, but the sky Scatterer draws stays blue (see Limits).
Below a craft flying over a deck of cloud is not the ground but the deck's tops, in the sun as the craft is, nothing between: thick cloud throws back some three quarters of the sunlight, white. From an airliner's window over an overcast the underside of the wing is nearly as bright as its top. Before 0.12.0 the mod lit a craft from below with the ground's colour seen through the air, a green twentieth of the sunlight, whatever was in between.
Natural Weather says, where the craft is, how much of the sky each of its three layers of cloud covers and how high their tops are. As much of what is below as the layers under the craft cover (one over another), the light from below is the tops': three quarters of the sunlight on them, as high as the sun is, a little tinted by the sky: half of what is below covered, half of the tops' light. Fog is not counted. Seen at 6,500 m over a held overcast at noon: an Aeris 4A's underside from a dull grey to nearly as bright as its top.
A spotlight's beam is not seen in clean air: there is nothing in it to throw the light back. In fog, rain, snow or dust the air is full of drops and grains, and the beam stands out as a cone of light, the more the thicker the air: a car's headlights in fog, a rover's lamps in a Duna dust storm. By day the sky's light drowns it; by night it is plain.
So every lamp that shines one way (the game's spotlights and the rovers' lights) on a craft within half a kilometre of the camera shows a beam from its glass along the way it points, as long as its light reaches (at most 80 m) and as wide as its cone, as bright as its light, as thick as the air is and as the dark lets it show. How thick: how much of the light a metre of air scatters, 3.9 over how far one can see (Koschmieder's rule), from the weather's own visibility, against thick fog's 200 m; and falling rain or snow through the beam, which the weather's visibility counts only in part. Clean air (some thirty kilometres) gives next to nothing, and so does a world without the weather mod. By day a beam keeps a twelfth of its strength. Drawn as the floodlights' beams are: a strip from the lamp, turned about its length to face the camera, in their picture of a beam seen from the side. Seen with the Crater Crawler's eleven lamps on the runway at night in fog. A setting, "Lamps' beams in fog and rain".
Anything that stands high enough to be in an aircraft's way is marked by night with red lamps at its top (the FAA's Advisory Circular 70/7460-1, ICAO's Annex 14): steady red lamps (some 32 candela) at the top corners of a wide building, and on a tall one a beacon that flashes red (some 2,000 candela, twenty to forty flashes a minute), as on the Vehicle Assembly Building at Kennedy and the masts round its pads. They are among the few colours of a launch site at night, beside the floodlights' white.
Each building of the space centre is measured once the scene has settled (its meshes, in its own frame). One that stands 40 m or more over its own foot gets red lamps at the corners of its roof where the roof is wide, or one at its top where it is narrow; from 75 m its top ones flash, thirty times a minute, rising and falling as a lamp's filament does. Lit from dusk to dawn with the floodlights. Measured at the space centre: the pad 43 m, the assembly building 119 m (its top flashing), the tracking station 41 m. The flag is left out (its cloth's box measured 305 m), and so is anything said to be over 160 m. A setting, "Red lamps on tall buildings".
By the rules every aircraft flies with (the FAA's 14 CFR 25.1385 to 25.1401): a red light at the left wingtip and a green one at the right, each seen from ahead and its own side; a white one at the tail, seen from behind; a red beacon on the fuselage that flashes; and white strobes at the wingtips, the brightest lights an aeroplane has, flashing on the runway and in the air by day as well as by night (most airliners two quick flashes every second or so). The game's aeroplanes have none, and a spaceplane taking off at night was a dark shape with an engine.
So a craft near the camera whose wings (lifting surfaces that are not control surfaces, adding up to at least one and a half of the game's wing measure, so not a rocket's fins) span four metres or more is given them: the wingtips are the outermost points of its wings either side, across the way its controlling part faces; the tail light is its rearmost point; the beacon is on top of it over its centre of mass. Position lights and the beacon by night; the strobes whenever it flies or rolls faster than 3 m/s, two flashes of a twentieth of a second a fifth apart every 1.2 s, each lighting the wing round it for that long (a cheap lamp, 9 m). A position light is not seen through the craft from its far side. A setting, "Aeroplanes' lights".
The light from all round is worked out as if the craft stood alone on a plain. Beside a hangar wall, in a crater, under an overhang, that is wrong twice over: half the sky is not there, and in its place is a wall, which, if the sun is on it, is far brighter than sky and the colour of whatever it is made of. So rays are cast from the middle of the craft, sixty-four of them spread evenly over every direction (eight a frame, so all are fresh within an eighth of a second), against the ground and the buildings, out to 400 metres.
- A ray that meets nothing is open sky. The sky's light from above is cut to the share of rays above that are open, and its light from each of north, east, south and west to the share open on that side.
- A ray that meets something has found a surface. What it is made of is looked up: the mean colour of its material's picture (read once for each material), or the planet's own colour for the ground. A second ray is cast from it towards the sun, past the ground, the buildings and the craft's own parts: if that one gets through, the sun is on the surface, by how squarely it faces the sun.
- Every surface found then lights the craft from where it is, in its colour, by the sun and sky on it. Near the ground this takes the place of the worked-out ground light, so the ground in the craft's own shadow throws back less than the ground beside it.
It is one set of rays for the whole scene, enough to tell a craft in the open from one by a wall and a wall in sun from one in shade; it is not a picture of the place, and no lamp's light is traced. It fades out by 1200 metres above the ground.
The space centre's buildings have windows that the game lights at dusk. Light from a lit window falls on the ground in front of its wall: as wide as the window and a little wider, brightest a step out from the foot of the wall, and further out and fainter the higher the window is.
Where the windows are is found on the buildings themselves: their meshes, looked up in the pictures that say where they glow, as the runway's lamps are found (above). The glowing bits are sorted by the way they face, then by how far out their wall stands, then along the wall, into stretches of lit wall; windows less than ten metres apart are one stretch. Only glass within thirty degrees of upright counts: glass in a roof lights the sky (the spaceplane hangar's great curved roof, taken for windows at first, lit its whole platform white), and less than two square metres of it is a lit sign, not windows. In front of each stretch a patch of warm light is laid on the ground, as wide as its windows and a little wider, reaching out from six to twenty-four metres by how high they are, and the brighter the more of the wall is glass. A stretch whose windows look at a wall close in front of them throws nothing, and the building's own wall is not lit: a window does not light the wall it is in. A few lamps of the cheap kind stand in front of the brightest stretches, for a craft or a kerbal standing there (they light those and not the ground, which a lamp of that kind only smears).
It follows the game's own switch for the windows, which lights them by the time of day and not in their materials: until 0.8.0 this read the materials' colour, which never changes, and so the window light was on by day as well. (Where a building's meshes cannot be read, as with a building some other mod has put there, its walls are found as they were before 0.8.0, by casting rays in at it, and each wall met is taken to have windows along twenty metres of it.)
The game lights a cockpit, and the crew's portraits, with its flat grey and with lamps of fixed strength, whatever is outside, and with a sun of its own that it turns with the real one, so that it shines in at the windows from the right side, with the cockpit's own walls throwing its shadows. Until 0.12 this mod gave the inside six tenths of the light all round outside, from no side in particular, in place of the grey. Since 0.12 the cabin is lit from its windows.
The windows. When a craft is flown, each kind of cockpit in it is looked at once, from where its crew's eyes are, in about two thousand directions, to the nearest of its own walls and fittings (on another thread, from a copy of its surfaces: about 2 ms on the game's own and 40 to 60 ms on the other, for the Mk1 pod's 28,000 triangles). Where nothing is met, the way is open: those are the openings through which the game shows the outside, glass or none. Neighbouring open ways are one window; the walls met just beside it say how far off it is and how big. The Mk1 pod has one window of about 300 cm² 39 cm from the pilot's eye, 6% of the pilot's view; the Mk1 Cockpit four, the two side panes about 1,500 cm² each, 17% of the view.
The light that comes in. Each window has a lamp of its own just inside it, shining in, of the light outside in the ways it looks: blue from a clear sky, grey under an overcast, the planet's colours when it is below, nothing from black space, and turning with the craft. It is as strong at the glass as that light is, and fades as a window's light fades, as one over the distance squared once past the window's own size (a lamp of that strength whose range is √(25·A/π) for a window of area A). What the walls throw back, of the windows' light and of the sun's where it stands outside a window (its patch on the inside is so much brighter than the rest that what it throws back fills a small cabin), lights everything else from all round: four tenths of what falls on the inside is thrown back, again and again. The cabin's own glow is added, all there is at night.
The game's sun in the cabin is given the strength and the colour the scene's camera drew the sun with: dimmed by the clouds, reddened at sunset, gone below the horizon. The game gave it the real sun's strength before the clouds dimmed it, in a white of its own: under an overcast it shone into the cabin in full, eight times what reached the craft, and at sunset it was white.
The cabin's own lamps are as strong as sunshine on what they light, and a cabin lit by them is lit evenly and as brightly as the day outside. Electric lamps are as strong by day as by night: beside daylight they are faint. So where the camera's eye follows the view, in the cockpit's own view they are at four tenths always (as they were by night, turned down to see out), and the eye, which reads the cockpit's picture, cabin and window together, opens for the dim cabin, as a camera inside one does: its windows go pale, light blue on a clear day and white under an overcast. Where the eye is not let follow the view (the camera's eye at 0), and for the crew's portraits, which are drawn apart from the picture the eye works on, nothing would make up for a dim cabin: there the lamps are all the way up by day and at four tenths in the dark, as before.
What it costs: about 0.07 ms a frame while a cockpit or a portrait is drawn.
A kerbal outside the craft needs nothing: it takes and throws the sun's shadows as parts do (seen by taking the same picture with the shadows off and on).
Asked for as: "In the hangar, when the spaceship is there, the tiny little kerbals on the ground walking through the rocket's shadow aren't affected. Same for the shadows of the building itself."
Why they are not, as the game ships. The assembly building and the hangar are not lit while the game runs: their light and shade were worked out once by their makers and painted onto the walls and floor (a lightmap), and the pools of light under the lamps are pictures laid on the floor. The crew, their trucks and the rocket are drawn afterwards by another camera, lit by lamps of their own that are the same all over the building; so a kerbal is as bright in the darkest corner as under a floodlight. And the rocket's shadow on the floor is not a shadow on the floor: it is an unseen sheet lying over it that darkens what is behind it by four tenths, wherever a faint lamp is hidden by the rocket. That lamp does shine on the crew and the rocket does shade them from it, but it is three tenths as bright as their other lamps, and nothing shows.
So each kerbal and each piece of a truck is made as bright as the floor it is on:
- The building's light. A small picture of the floor is taken from straight above (192 dots across, from a little over head height, so that the gantries are not in it), twice: as it is drawn, and with only its paint, by a shader that takes no light. The first divided by the second is the light on each spot of the floor, whatever is painted there: bright under the lamps, dim in the bays at the sides. Only the pieces of the building with painted light, and the pools of light over them, are in the picture; everything else is hidden from that one eye while it looks. Each of the crew takes the light of the spot it is over, against the light of the open floor. Outside the building they are as the game has them. The building does not change, so the floor is looked at three times as the scene starts and then once in a minute and a half.
- The rocket's shadow. From each of them three lines, a little apart so that the shadow's edge is soft, are drawn towards the lamp that throws the rocket's shadow. Where parts are in the way it is darkened by as much as the sheet darkens the floor, and a tenth more for the lamp it has lost.
Nothing is added to what is drawn and no lamp is changed: each piece's own colour is turned down (between a third and one and a fifth of what it was), and put back when this is switched off. Pieces that only glow, a lamp, a marshal's wand, are left alone.
It costs 0.05 thousandths of a second a frame in the assembly building (46 kerbals and trucks, in 529 pieces), and a tenth of a second once as the building is entered.
Nebulae, far galaxies and brighter stars, added to the game's own sky: asked for as "beautiful, gorgeous nebulas... but still look like space", so it is mostly black. Seven to nine nebulae, most on the band of the galaxy and more towards its heart: glowing gas (red at the heart, teal or blue at the edges, crossed by dark lanes), dust lit blue by stars, and the torn shell of a star that blew up, degrees across as the Veil and the Vela remnant are: arcs of thin threads round a ragged rim, brighter on one side, broken where the shell met thinner gas, teal and red wound through each other (since 0.13.0: before, a round ring even all the way round with a star at its middle, which read as a lens's ghost, a green ring high in the night sky); two or three small galaxies well off the band; and about five hundred stars brighter than the game's own, in the colours stars have.
No picture is shipped. Each of the sky's six faces is worked out from noise on its own thread when the game starts (1024 by 1024, about a second in all), from a number that can be changed for another sky. Where the band lies is found from the game's own sky: each face is shrunk and read, and the band is the plane the bright dots lie nearest (0.019 off it in the sky this was made on, where 0.333 would be no band at all). So the nebulae sit on the band of whatever sky is installed.
It is drawn as six more faces just inside the game's six, with light added to what is there, by one of the game's own shaders. The game dims its sky in air by day and when the sun is in view, and the camera's eye dims it when anything bright is; the added faces read back how much the game's own have been dimmed and follow. (A glow was laid along the band itself at first. It lay over the game's Milky Way like a haze and was taken out.)
The game draws every world as a ball, and one smaller than a dot of the screen as nothing: from Kerbin by night Jool, Duna and Eve were not in the sky at all, though worlds like them are the brightest things in a real night sky after the moon. Now each world too small to show is a point of light as bright as it really is, worked out as an astronomer works out a planet's brightness: from its size, from how much of the sun's light it throws back (the mean colour of its own picture, as for the light of other worlds: Jool green, Duna pale salmon, Eve violet), from how much of its lit side is turned this way, and from how far it is from the sun and from here. In magnitudes, the sun from Kerbin being -26.74: from the space centre on the night of the tests Duna was -1.5 and Jool -1.2, brighter than any of the game's stars, Ike 1.8, Jool's larger moons 4.4 to 5.2 beside it, Eeloo 8.4 (too faint to see); Eve, near the sun, -2.4 to -2.6.
They are set against the game's own sky, measured as it is drawn: its camera made to draw the whole sky at full brightness, a face of a cube at a time, and every star found in it (95,000 dots brighter than all round them). Its fourth brightest is taken as of magnitude 0, as the fourth of ours is (Arcturus); its brightest is then -0.3 and its fifteenth 0.5. The game's sky has less between its brightest and its faintest than a real one (its brightest is only twice its fifteenth, where Sirius is ten times ours), so the worlds are set against its brightest, as an eye looking for a planet sets it against the brightest stars near it. The deep sky's added stars are fainter than the game's brightest: the measure is the same with it and without.
A point is drawn as a camera sees one: a soft dot about a dot of the screen across (as narrow as it can be and still add up to the same light wherever it falls between dots), with a faint glow round it, as a lens and an eye throw one. Brighter than the picture can hold, its middle burns out and it looks wider, as bright stars do in photographs; it keeps its hue as it does (an eye sees Mars orange though a camera burns its middle white) and goes to white only where it is many times over. Nothing is brighter than magnitude -5 as a point: anything brighter in a real sky is a disc.
It is drawn into the game's sky of stars by the camera that draws it, first of all, so whatever is in front hides it: a world, the ground, a cloud. It is dimmed with the stars: by the sky's light at dusk and by day (below), with the sun in sight, and by the camera's eye when something bright is in view. Low down it is dimmed and reddened by the air it is seen through (Kasten and Young's air mass): Eve setting at the space centre, a degree up, was a faint dark red. A world in its planet's shadow is dark. As a world grows past a dot or so across (zoomed in, or near: Minmus from Kerbin is 1.6 to 2.4 dots) its light eases into what the game's own drawing of it shows, a disc as bright as sunlit ground is by day, and by three dots the game's drawing has it. (A point as bright as the stars' measure makes it, laid over Minmus, magnitude -10.8 from Kerbin, was a dazzle many times its size. A photograph taken for the stars burns the moon out white; the game draws its worlds by day's measure whatever the hour.)
Craft too far off for the game to draw are points too, in orbit or in the air: each by how much it shows from the side (every part as wide as its widest joint and as long as its joints are apart, a solar panel two square metres more), a grey of a third, lit unless the world below is in the way. After sunset a craft in a low orbit catches the sun overhead and goes out as it passes into the shadow: the test save's probe of 13 parts, 80 km up and some 200 km off, crossed the northern sky at dawn at magnitude 3, a faint moving star, as a small satellite is. Craft near enough to be loaded are the game's to draw, and a point only while one is smaller than three dots.
Each point is drawn as two small squares, each with a picture of a dot of a given light (fourteen of them, each twice the light of the one before): the one below its light and the one above, weighed between them. Drawn first as rings of coloured corners, a point came out 15 to 40% brighter on Direct3D than on OpenGL with the game's anti-aliasing (on the PC, beside the same view on OpenGL): there a pixel only partly covered by one of the small triangles at a point's middle takes the colour worked out at the pixel's own middle, which can lie past the triangle's tip, where the colours run on above the brightest. A picture gives what is in it wherever it is read. (On the Mac's OpenGL the anti-aliasing changed nothing either way.)
Seen in motion (the view turned 3 degrees a second, filmed frame by frame, the motion tool on it): no flicker, jumps or jitter;
a point's light held to 1.3% from one frame to the next as rings, 0.3% as pictures, the game's stars round it 0.8 to 2.6%.
It costs 0.07 thousandths of a second a frame with ten points in the sky (the development build's timer, the Mac; 0.16 as
rings, 0.97 before their corners were worked out once). Each world's colour is read off its picture once in a game, one world
a frame. Beside Parallax it is read off Parallax's own colour map (_ColorMap), which it fills only once it has loaded that
world's picture (Kerbin's and the Mun's at first); until then _MainTex holds Unity's white stand-in, four dots by four,
which is no picture of the world (read as one, every world was taken as white: found on the PC). So a stand-in is taken as
no picture, the world is taken meanwhile as it looks without Parallax (the stock worlds' mean colours, read off the
pictures the game comes with; grey for any other world), and its picture is looked for again every ten seconds. The same
colour lights what a world shines on (moonlight). Not drawn in the map view (the map has its own marks) nor in the
tracking station.
The idea is Distant Object Enhancement's (CC BY 4.0: TheDarkBadger, MOARdV and others): far worlds and craft as points of light. It is worked out anew here, with the brightness from the physics in place of its tuned curves; none of its code is used.
The game hides its stars in air until the sun is some 25 degrees below the horizon and then lets them out within a degree or two: its fade by the hour is multiplied by the air's pressure in the wrong units, and comes to about 130 at the space centre where it means about 0.2. And at night in air it keeps them at two fifths of their brightness, as if the air took more than two magnitudes of their light, where clean air takes a quarter of one overhead.
Here they come out as a real sky's do. An eye sees stars to magnitude -2 at sunset, 0 with the sun 3 degrees down, 2 at 6, 3.5 at 9, 4.5 at 12, 5.5 at 15 and 6.5 at 18, and a real sky has 4 stars brighter than 0, 48 brighter than 2, about 300 than 3.5, 900 than 4.5 and 2,800 than 5.5. So at each height of the sun the game's sky is dimmed until as many of its stars are brighter than the faintest it shows at night (taken from the census above). By count and not by brightness, because the game's sky has less between its brightest and its faintest than a real one: dimmed by the sky's light as a real sky is, nearly all of its stars went out together (7 in a view that had 187 at night, with the sun 12 degrees down). Counted in one view from the hill west of the space centre, the sun held at each height: 3 stars at 3 degrees down, 2 at 6, 13 at 9, 39 at 12, 81 at 15, 215 at 18. Thinner air lights the sky less and lets them out sooner (Duna), thicker later (Eve). At night they are as bright as the air lets them be: on the hill, 3.4 km up, two and a half times the light the game gave them, some six times at sea level. The sun in sight still dims them as the game does, and the camera's eye when anything bright is; out of air the game's own is left (it dims them only for the sun in sight). The deep sky and the far lights follow.
A visor is a curved mirror with the world in it, as every photograph of anyone in a spacesuit shows: the ground and its horizon, the craft beside them, the sun, whoever holds the camera. The game draws its visors' glass with Unity's shader for real materials ("Standard (Specular setup)", see-through), which mirrors whatever a reflection probe round it holds. The game's only probe sits on its camera, is off unless its graphics settings turn reflections on, and then holds the ground and the planets against one flat colour for the sky. So the visor showed nothing of where the kerbal was.
Now a probe of the mod's own sits round the head of the kerbal outside nearest the camera (within 60 m, and only while their visor shows on the screen at ten dots or more), and what it holds is drawn from that head as a cube of six pictures, each laid in three passes, as the game draws its own view: the sky of stars, then the worlds far off, then the scene round about (craft, ground, other kerbals), the kerbal's own body left out. Drawn as light past white, as the game's near camera draws with TUFX, so that the camera's eye stops it down with the rest of the picture (drawn into a picture of nought to one, at first, the sunlit Mun was white in it). The glass mirrors it as the game's shader works out, by the angle: a tenth or so of it straight on, nearly all at a glance. Through the clear visor, over a lit face, that is faint, as it is through real clear glass; the dark sun visor (lowered from the kerbal's menu) shows it plainly: on the Mun, the grey ground and its horizon across the gold below the sun, as in the photographs from the Moon. Nothing new on Direct3D: the game's own shader does the mirroring.
Drawn a face every other frame while the kerbal moves (the cube is fixed in the world, not to the camera, so only their moving changes it) and a face every eighth frame while they stand; drawn without shadows and with the sun alone lit by the pixel (in a small curved mirror a shadow is a few dots). Drawn a face every frame with the game's own settings, on the floodlit pad, it cost 4 to 8 thousandths of a second a frame; as now, on the Mun walking and on the pad standing, nothing that could be measured against the frame's own wander.
The idea, a cube drawn a face at a time from the head in three passes, is TextureReplacerReplaced's (MIT: shaw, then HaArLiNsH and others), which gives visors and windows real reflections with a shader of its own; done here with the game's own visor shader and a probe.
It is read off the picture the game draws each planet with from afar: a small copy of it (512 by 256) is made once for each body, and the colour is the average round the point under the craft. How far round goes by height, because half of the light from the ground comes from within the craft's own height of the point beneath it: a few kilometres on the ground, the whole visible disc from orbit.
Close to the ground only ground of the kind the craft is over counts, land or water. A dot of that picture is seven kilometres across on Kerbin, and the launch site is on a beach: without this, a rocket on the pad was lit from below by the sea.
(Which way round the picture lies was found by writing the copy out and trying every way against eleven known places on Kerbin. Ten of the eleven agree with one way and no other.)
The game shows colours as they are stored, but a probe is taken as light, where twice the number is twice the light, and turned into what is shown afterwards. Measured at night on the pad: a probe of 0.24 from all round showed twice as bright as the game's own flat 0.24. So everything the settings and the colours say is turned into light first, added up, and handed over as light.
(The weather's veil, 0.10.0: two passes over the whole picture, each reading the depth picture once, and the weather asked four times a second. In rain on the pad, the frame-rate cap lifted, the veil switched on and off by turns: 31.6 and 27.0 thousandths of a second a frame while the scene was still settling, each faster than the one before, then 20.1 with it and 20.4 without: too little to tell from the noise.)
The light from all round: a few dozen sums a frame, and twice a second a reading of the ground's colour. The lamps: one of the costly kind for each flame (everything within its reach is drawn once more), up to three; everything else is of the kind the shaders take for nothing.
Measured on the pad with the game's frame-rate cap lifted (an Apple M-series Mac, 1280 by 720, with Scatterer, EVE, TUFX and Waterfall): by day the whole mod without the film look cost 0.2 thousandths of a second a frame of 15.6; at night with the floodlights on, 0.1 of 14.2. The film look, once the hitch described above was gone, could not be told from the noise of the measurement (three tenths of a thousandth either way): TUFX's own profile was already doing a glow, and what is added is the curve and the darkened creases.
Measured again on 2026-10-17 with Keystone's meter (each mod's own time on the game's main thread, which is what holds this Mac up), on the pad: 0.55 thousandths of a second a frame by day and 0.65 at night with the floodlights and the runway's lamps on, after two cuts. Method by method (the development build's timer): the light worked out each frame 0.3 (of which the rays 0.1), its handing to each camera 0.1 to 0.2 (with the cockpits' light, 0.07), the floodlights 0.1, the runway's lamps 0.05. Until then the floodlights' glare and beams and the runway's 108 glows were turned to every camera that drew them: on OpenGL that is two cameras a frame, the near and the far, standing at the same place and turned the same way, and the cards were turned twice, 0.25 and 0.40 thousandths of a second a frame. Now they are turned once a frame, and not at all for a site or a row the camera has not moved against since: 0.05 and 0.04.
The runway's lamps and the windows' light are found once in a scene: the runway's 108 lamps in 35 to 85 thousandths of a second, each building's windows in 4 to 55 (the research complex, the largest, 55), when they first come on. Drawn, they are a mesh of pools and one of glows for each of the game's ten lamp meshes, one mesh of light for each building, the glows turned to the camera every frame (108 of them), and six lamps of the cheap kind near the craft. On the runway at night, the frame-rate cap lifted, the lamps on and off by turns: 16.97 and 16.98 thousandths of a second a frame with them, 16.89 and 16.94 without, which is within the noise of the measurement (the frame time sat near the display's sixty a second, which can hide small costs). The window light was not measured on its own.
The floodlights' model and its two pictures are read once a game, when the first launch site's floodlights are put up
(the space centre or the pad): 0.44 to 0.53 s (Warm Start's probe, 2026-10-19 and 20), most of it the two pictures of
2048 (unpacked from their files, their smaller copies made and all of it squeezed into the graphics card's own format, on
the game's thread). Since 0.12.0 what is made of each picture is kept beside it (PluginData/kept, 5.6 MB each) and read
back while its file is what it was: the model and its pictures in 29 ms, the pictures 14 ms of that (the next start after
the first, 2026-10-20). If the fixture is ever thrown away and read again in a game, the log says what of it was gone.
The shafts of sunlight, measured the same way at sunrise looking into the sun: 0.7 thousandths of a second a frame of 13, and nothing when the sun is not in view. Hardly any of that is the work itself. Each change from drawing one picture to drawing another costs about a seventh of a thousandth here, whatever the size of the pictures, so the first version, in six steps, cost 1.1, and drawing the shafts out at a quarter of the size instead of a half saved nothing at all; what saved a third was doing it in four steps. The blacking out of pixels that are not numbers could not be told from no blacking out.
The engines' lamps (the flame's own and the three round it) hang from the model of the engine's part, so that where Smooth Running carries the craft on between the game's physics steps they go with it; left loose in the scene they would stand behind the flame by up to a step's travel (2026-10-18). The lamps where a flame meets the ground stay on the ground.
The camera's eye meters a small copy of the view (up to 96 by 54 points), read back from the graphics card. On the Mac's OpenGL, where Unity has no asynchronous read, it was read at the start of a frame three times a second, which still waited for whatever the card had left of the last frame. Now it goes through Keystone's read-back in two halves (each read may hold 64 KB), by Volumetric Explosions' library where that is installed, and the game does not wait; Direct3D and Metal read it without waiting as before. With "The camera's eye" at 0 nothing is read at all.