Improve color handling approach

src/graphics/rendering/shaders/distance-fs.glsl

@@ -6,21 +6,28 @@ uniform float maxMinDistance;
 uniform float distanceNdcPixelSize;
 in vec2 position;
 
+uniform sampler2D palette;
+
 #define WEBGL2_IS_AVAILABLE
 
+vec4 readFromPalette(int index) {
+  return texture(palette, vec2((float(index) + 0.5) / {paletteSize}, 0.5));
+}
+
 {macroDefinitions}
 
 {declarations}
 
-out vec2 fragmentColor;
+layout(location = 0) out vec4 fragmentColor;
+layout(location = 1) out float distanceValue;
 
 void main() {
-    float minDistance = maxMinDistance;
-    float color = 0.0;
-
-    float objectMinDistance, objectColor;
+    float minDistance = maxMinDistance, objectMinDistance;
+    vec4 color = {backgroundColor};
+    vec4 objectColor;
 
     {functionCalls}
 
-    fragmentColor = vec2(minDistance, color);
+    distanceValue = minDistance;
+    fragmentColor = color;
 }