White Escapes New Normal Map Equator

This is an issue related to the new normal map from 20902e3 . I'm expecting the color white to fall around #dada80 which is (45 degrees theta, 0 degrees phi) in spherical coordinates or (0.7071, 0.7071, 0.0) in Cartesian coordinates.

Not sure what to suggest for the current approach because I 1. try to use fewer trigonometric functions and 2. allow the normal sphere to be flipped on the z axis. Below is a snippet of some simplified Lua code.

local xi = center
local yi = center

local r255 = hexSrgb & 0xff
local g255 = (hexSrgb >> 0x08) & 0xff

local x = (r255 + r255 - 255) / 255.0
local y = (255 - (g255 + g255)) / 255.0

local sqMag2d = x * x + y * y
if sqMag2d > 0.000031 then
    local invMag2d = 1.0 / math.sqrt(sqMag2d)
    local xn2d = x * invMag2d
    local yn2d = y * invMag2d
    local xu = 0.5
    local yu = 0.5
    if sqMag2d >= 1.0 then
        xu = xn2d * 0.5 + 0.5
        yu = yn2d * 0.5 + 0.5
    else
        local b255 = (hexSrgb >> 0x10) & 0xff
        local z = (b255 + b255 - 255) / 255.0
        local zn3d = z / math.sqrt(sqMag2d + z * z)

        -- cos(asin(z)) == sqrt(1 - z * z)
        local dist = math.sqrt(1.0 - zn3d * zn3d)
        local xn3d = xn2d * dist
        local yn3d = yn2d * dist

        xu = xn3d * 0.5 + 0.5
        yu = yn3d * 0.5 + 0.5
    end

    xi = floor(0.5 + xu * size)
    yi = floor(0.5 + yu * size)
end

Not sure, but some users may expect a color like white to be normalized in advance, making white into #c9c9c9, (45 degrees theta, 35 degrees phi) or (0.577, 0.577, 0.577). For a color picker, though, I prefer clamping so that the reticule doesn't bounce around on the wheel.

I think you refer to this right?

I guess in ColorWheel::onPaintMainArea(), before we call paintColorIndicator() when can just clamp the distance when we use red/green values only:

diff --git a/src/app/ui/color_wheel.cpp b/src/app/ui/color_wheel.cpp
index 6f0b0ea2b..187b9e2c9 100644
--- a/src/app/ui/color_wheel.cpp
+++ b/src/app/ui/color_wheel.cpp
@@ -344,9 +344,14 @@ void ColorWheel::onPaintMainArea(ui::Graphics* g, const gfx::Rect& rc)
       double x, y;
 
       double approximationThreshold = (246.0 / 255.0) * 2.0 - 1.0;
-      if (normalizedBlue > approximationThreshold) { // If blue is too high, we use red and green only as approximation
-        x = normalizedRed * m_wheelRadius;
-        y = -normalizedGreen * m_wheelRadius;
+      if (normalizedBlue > approximationThreshold) {
+        // If blue is too high, we use red and green only as approximation
+        double angle = std::atan2(normalizedGreen, normalizedRed);
+        double dist = std::sqrt(normalizedRed*normalizedRed + normalizedGreen*normalizedGreen);
+        dist = std::clamp(dist, 0.0, 1.0);
+
+        x = std::cos(angle) * m_wheelRadius * dist;
+        y = -std::sin(angle) * m_wheelRadius * dist;
       }
       else {
         double normalizedDistance = std::cos(std::asin(normalizedBlue));

Don't put the color indicator in normal map outside the wheel (fix as…

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White Escapes New Normal Map Equator #3595

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White Escapes New Normal Map Equator #3595

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dacap commented on Nov 17, 2022

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