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[LK8000#1142] Fix Terrain Drawing for Altitude lower than 0 and great…
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…er than 4095m

land surface elevation range of earth are [-428m , 8848m], range of color ramp are [0, 255]

currently we clip surface elevation to [0 - 4096], so all elevation bellow 0 are draw like sea (if topology doesn't include coast_area shape) and all elevation higher than 4096 are draw like invalid terrain (LCD Green).

for fix this problem :
 1 - calculate span of visible elevation
 2 - shift elevation by min of this range ( result range is [0 - 9276] )
 3 - scale result to range [0 - 255]
	for speed reason, scaling is made using bit shift, ( power of 2 scaling factor).

of course same algorithm are used for build color ramp.
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@brunotl
brunotl committed Oct 19, 2017
1 parent bc2439a commit 94d7924
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Showing 2 changed files with 76 additions and 41 deletions.
2 changes: 1 addition & 1 deletion Common/Header/Terrain.h
View file
Expand Up @@ -8,7 +8,7 @@

typedef struct _COLORRAMP
{
unsigned short h;
int16_t h;
unsigned char r;
unsigned char g;
unsigned char b;
Expand Down
115 changes: 75 additions & 40 deletions Common/Source/MapDraw/DrawTerrain.cpp
View file
Expand Up @@ -19,6 +19,7 @@

#include "./ColorRamps.h"
#include "Kobo/Model.hpp"
#include "Util/Clamp.hpp"

//
// Choose the scale threshold for disabling shading. This happens at low zoom levels.
Expand All @@ -32,8 +33,6 @@
#define NOSHADING_REALSCALE 14.3 // After 20Km zoom 14.3
#endif

unsigned short minalt = TERRAIN_INVALID;

static short autobr=128;

extern bool FastZoom;
Expand All @@ -47,8 +46,9 @@ extern void rgb_lightness( uint8_t &r, uint8_t &g, uint8_t &b, float lightness);


static const COLORRAMP* lastColorRamp = NULL;
static unsigned last_height_scale = 0;

static void ColorRampLookup(const short h,
static void ColorRampLookup(const int16_t h,
uint8_t &r, uint8_t &g, uint8_t &b,
const COLORRAMP* ramp_colors, const int numramp,
const unsigned char interp_levels)
Expand All @@ -58,9 +58,9 @@ static void ColorRampLookup(const short h,

for (unsigned int i = numramp - 1; i--;) {
if (h >= ramp_colors[i].h) {
const unsigned short f = (h - ramp_colors[i].h) * is / (ramp_colors[i + 1].h - ramp_colors[i].h);
const int16_t f = (h - ramp_colors[i].h) * is / (ramp_colors[i + 1].h - ramp_colors[i].h);

const unsigned short of = is - f;
const int16_t of = is - f;

r = (f * ramp_colors[i + 1].r + of * ramp_colors[i].r) >> interp_levels;
g = (f * ramp_colors[i + 1].g + of * ramp_colors[i].g) >> interp_levels;
Expand Down Expand Up @@ -172,9 +172,9 @@ class TerrainRenderer {

TESTBENCH_DO_ONLY(5,StartupStore(_T("... Terrain quant=%d ixs=%d iys=%d TOTAL=%d\n"),dtquant,ixs,iys,ixs*iys));

hBuf = (unsigned short*) malloc(sizeof (unsigned short)*ixs * iys);
hBuf = (int16_t*) malloc(sizeof(int16_t)*ixs * iys);
if (!hBuf) {
StartupStore(_T("------ TerrainRenderer: malloc(%u) failed!%s"), (unsigned)(sizeof(unsigned short)*ixs*iys), NEWLINE);
StartupStore(_T("------ TerrainRenderer: malloc(%u) failed!%s"), (unsigned)(sizeof(int16_t)*ixs*iys), NEWLINE);
OutOfMemory(_T(__FILE__), __LINE__);
//
// We *must* disable terrain at this point.
Expand All @@ -184,7 +184,7 @@ class TerrainRenderer {
}
#if TESTBENCH
else {
StartupStore(_T(". TerrainRenderer: malloc(%u) ok"), (unsigned)(sizeof(unsigned short)*ixs*iys));
StartupStore(_T(". TerrainRenderer: malloc(%u) ok"), (unsigned)(sizeof(int16_t)*ixs*iys));
}
#endif

Expand All @@ -196,6 +196,7 @@ class TerrainRenderer {
}
// Reset this, so ColorTable will reload colors
lastColorRamp = NULL;
last_height_scale = 0;

// this is validating terrain construction
_ready = true;
Expand Down Expand Up @@ -250,12 +251,15 @@ class TerrainRenderer {
static constexpr int oversampling = 1; //no oversampling if no "Blur"
#endif

unsigned short *hBuf;
int16_t *hBuf;
BGRColor *colorBuf;
bool do_shading;
static constexpr int interp_levels = 8;
const COLORRAMP* color_ramp;
static constexpr unsigned int height_scale = 4;

unsigned height_scale; // scale factor ((height - height_min + 1) << height_scale) must be in [0 - 255] range
int16_t height_min; // lower height visible terrain
int16_t height_max; // highter height visible terrain

public:

Expand Down Expand Up @@ -375,8 +379,14 @@ class TerrainRenderer {
const double ac2 = sint*InvDrawScale;
const double ac3 = cost*InvDrawScale;

height_scale = 0;

// we need local variable for compatibility with all implementation of opemmp reduction
int16_t _height_min = std::numeric_limits<int16_t>::max();
int16_t _height_max = std::numeric_limits<int16_t>::min();

#if defined(_OPENMP)
#pragma omp parallel for
#pragma omp parallel for reduction(max : _height_max) reduction(min : _height_min)
#endif
for (unsigned int iy=0; iy < iys; iy++) {
const int y = Y0 + (iy*dtquant);
Expand All @@ -388,33 +398,49 @@ class TerrainRenderer {
const double Y = ac1 - x*ac2;
const double X = PanLongitude + (invfastcosine(Y) * ((x * ac3) - cc1));

unsigned short& hDst = hBuf[iy*ixs+ix];
// this is setting to 0 any negative terrain value and can be a problem for dutch people
// myhbuf cannot load negative values!
hDst = std::max<short>(GetHeight(Y, X),0);
int16_t& hDst = hBuf[iy*ixs+ix];

/*
* Terrain height can be negative.
* do not clip height to 0 here, otherwise all height below 0
* will be painted like sea if topology does not contains coast_area
*
* all height will be sifted by #height_min in #TerrainRenderer::Slope method for ColorRamp lookup.
*/
hDst = GetHeight(Y, X);

if(hDst != TERRAIN_INVALID) {
_height_min = std::min(_height_min, hDst);
_height_max = std::max(_height_max, hDst);
}
}
}
height_min = _height_min;
height_max = _height_max;

if (!terrain_minalt[TerrainRamp]) {
minalt = 0; //@ 101110
} else {
minalt = *std::min_element(hBuf, hBuf+(ixs*iys));
// if ColorRamp is not relative to min height of visible terrain, we only use negative height_min.
height_min = std::min<int16_t>(0, height_min);
}


if (TerrainRamp == 13) {
if (TerrainRamp == 13) { // GA Relative
if (!GPS_INFO.NAVWarning) {
if (CALCULATED_INFO.Flying) {
minalt = (unsigned short) GPS_INFO.Altitude - 150; // 500ft
height_min = (int16_t) GPS_INFO.Altitude - 150; // 500ft
} else {
minalt = (unsigned short) GPS_INFO.Altitude + 100; // 330ft
height_min = (int16_t) GPS_INFO.Altitude + 100; // 330ft
}
} else {
minalt += 150;
height_min += 150;
}
}

// StartupStore(_T("... MinAlt=%d MaxAlt=%d Multiplier=%.3f\n"),minalt,maxalt, (double)((double)maxalt/(double)(maxalt-minalt)));
const int16_t height_span = height_max - height_min + 1;
while((height_span >> height_scale) >= 255) {
++height_scale;
}

// StartupStore(_T("... MinAlt=%d MaxAlt=%d height_scale=%d\n"),height_min, height_max, height_scale);

}

Expand All @@ -436,7 +462,7 @@ class TerrainRenderer {
const unsigned int ixsepx = cixs*epx;
const unsigned int ixsright = cixs - 1 - iepx;
const unsigned int iysbottom = ciys - iepx;
const int hscale = max(1, (int) (pixelsize_d));
const int hscale = std::max<int>(1, pixelsize_d);

int tc=1;
if (AutoContrast) {
Expand Down Expand Up @@ -472,7 +498,7 @@ class TerrainRenderer {
const BGRColor* oColorBuf = colorBuf + 64 * 256;
if (!sbuf->GetBuffer()) return;

#if defined(_OPENMP)
#if defined(_OPENMP)
#pragma omp parallel for
#endif
for (unsigned int y = 0; y < ciys; ++y) {
Expand All @@ -499,29 +525,34 @@ class TerrainRenderer {
p31s = p31*hscale;

BGRColor* RowBuf = sbuf->GetRow(y);
unsigned short *RowthBuf = &hBuf[y*cixs];
int16_t *RowthBuf = &hBuf[y*cixs];

for (unsigned int x = 0; x < cixs; ++x) {

BGRColor* imageBuf = &RowBuf[x];
unsigned short *thBuf = &RowthBuf[x];
int16_t *thBuf = &RowthBuf[x];

int16_t h = *thBuf;

unsigned short h = *thBuf;
// FIX here Netherland dutch terrain problem
// if >=0 then the sea disappears...
if (h != TERRAIN_INVALID) {
// if (h==0 && LKWaterThreshold==0) { // no LKM coasts, and water altitude
if (h == LKWaterThreshold) { // see above.. h cannot be -1000.. so only when LKW is 0 h can be equal
*imageBuf = BGRColor(85, 160, 255); // set water color #55 A0 FF
continue;
}
h = h - minalt + 1;

int p20, p22;
// this fix rendering of negative elevation terrain ( 45 country are concerned ... )
h = h - height_min + 1;
assert(TerrainRamp == 13 || h >= 0); // height_min is wrong...

h = min(255, h >> height_scale);
// no need to calculate slope if undefined height or sea level
h = h >> height_scale;
assert(TerrainRamp == 13 || h < 256); // height_scale is wrong ...

h = Clamp<int16_t>(h, 0, 254); // avoid buffer overflow....

int p20, p22;
// no need to calculate slope if undefined height or sea level
if (do_shading) {
if (x < ixsright) {
p20 = iepx;
Expand Down Expand Up @@ -561,7 +592,7 @@ class TerrainRenderer {

// p20 and p31 are never 0... so only p22 or p32 can be zero
// if both are zero, the vector is 0,0,1 so there is no need
// to normalise the vector
// to normalize the vector
int dd0 = p22*p31;
int dd1 = p20*p32;
int dd2 = p20*p31s;
Expand All @@ -575,7 +606,7 @@ class TerrainRenderer {
int mag = isqrt4(dd0 * dd0 + dd1 * dd1 + dd2 * dd2);
if (mag > 0) {
mag = (dd2 * sz + dd0 * sx + dd1 * sy) / mag;
mag = max(-64, min(63, (mag - sz) * tc_in_use / 128));
mag = Clamp((mag - sz) * tc_in_use / 128, -64, 63);
*imageBuf = oColorBuf[h + mag * 256];
} else {
*imageBuf = oColorBuf[h];
Expand All @@ -596,11 +627,12 @@ class TerrainRenderer {

void ColorTable() {
color_ramp = &terrain_colors[TerrainRamp][0];
if (color_ramp == lastColorRamp) {
if (color_ramp == lastColorRamp && height_scale == last_height_scale) {
// no need to update the color table
return;
}
lastColorRamp = color_ramp;
last_height_scale = height_scale;

for (int i = 0; i < 256; i++) {
for (int mag = -64; mag < 64; mag++) {
Expand Down Expand Up @@ -757,11 +789,14 @@ bool DrawTerrain(LKSurface& Surface, const RECT& rc, const ScreenProjection& _Pr
thighlight_b = terrain_highlight[TerrainRamp].b;
thighlight_h = terrain_highlight[TerrainRamp].h;

trenderer->SetShading();
trenderer->ColorTable();
// step 1: fill height buffer
// step 0: fill height buffer
trenderer->Height({rc.left, rc.top}, _Proj);

// step 1: update color table
// need to be done after fill height buffer because depends of min
// and max height of terrain
trenderer->SetShading();
trenderer->ColorTable();

// step 2: calculate sunlight vector

Expand Down

3 comments on commit 94d7924

@pventafridda
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@pventafridda pventafridda commented on 94d7924 Nov 4, 2017 •
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Are you sure that DEM below zero is drawn as water? That was not was I made to solve the Netherland problem, the problem in Italy and Benelux, Uk etc.

See OpenCloseTopology. DEM TERRAIN can even be -500m without being water.
I did the fix long time ago, working fine.

@brunotl
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@brunotl brunotl commented on 94d7924 Nov 4, 2017 •
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yes i'm sure, explained in commit comment :

if topology doesn't include coast_area shape

@pventafridda
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@pventafridda pventafridda commented on 94d7924 Nov 4, 2017 via email

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