Adjustments to HDR color saturation.

Color saturation is internally multiplied by an adjustment factor so that it does not result in colors that appear way too saturated compared to SDR. Additionally, gamut expansion is now fixed to 0.2, which is a good compromise between allowing high saturation colors to transit to higher color spaces and keeping the look of the game as close as possible to the original SDR.

Resources/Shaders/oolite-final-hdr.fragment

@@ -16,6 +16,8 @@ uniform float		uSaturation;
 #define SMPTE_ST2084MAXNITS	10000.0
 #define MAXCLLNITS			1000.0
 #define HDR_HEATMAP			0
+#define SATURATION_ADJUSTMENT	0.825 //adjustment factor to better approach SDR saturation
+#define GAMUT_EXPANSION_AMOUNT	0.2 //0.0f .. 1.0f - best results if this is kept low
 
 
 
@@ -729,7 +731,7 @@ void main()
 	t = t * t / (12.0 + t);
 
 	// apply saturation
-	hdrColor = max(saturationMatrix(uSaturation) * hdrColor, vec3(0.0));
+	hdrColor = max(saturationMatrix(uSaturation * SATURATION_ADJUSTMENT) * hdrColor, vec3(0.0));
 
 	// mastering to 1000 nits max luminance
 	hdrColor = min(hdrColor, vec3(MAXCLLNITS * 0.0125));
@@ -744,7 +746,7 @@ void main()
 	vec3 result = ACESFilmRec2020OrReinhardHDR(mix(hdrColor, luma, clamp(t * 80 / uMaxBrightness, 0.0, 1.0)) * uPaperWhiteBrightness * 0.0125);
 
 	// gamut expansion here
-	result = expandGamut(result, uSaturation * 0.05f);
+	result = expandGamut(result, GAMUT_EXPANSION_AMOUNT);
 
 #if HDR_HEATMAP
 	{