Improve skybox

shaders/color.frag

@@ -10,9 +10,26 @@ layout(location = 0) out vec4 out_color;
 layout(location = 1) out vec4 out_motion;
 #endif
 
+// the skydome vertex colours carry Perez luminance scaled by a fixed exposure
+// (see CSkyDome::SetExposure), so the circumsolar region and the horizon band
+// routinely land well above 1.0. hard-clipping them, as this shader used to do,
+// flattened everything within ~20 degrees of the sun - and most of the lower sky -
+// into one solid white patch. compress the top end instead: below the knee the
+// response is unchanged, above it it rolls off towards SKY_SHOULDER_WHITE, so the
+// brightness gradient around the sun survives and the patch keeps a soft edge.
+const float SKY_SHOULDER_KNEE = 0.25;
+const float SKY_SHOULDER_WHITE = 0.95;
+
+vec3 sky_shoulder(vec3 color)
+{
+	const float range = SKY_SHOULDER_WHITE - SKY_SHOULDER_KNEE;
+	vec3 excess = max(color - vec3(SKY_SHOULDER_KNEE), vec3(0.0));
+	return min(color, vec3(SKY_SHOULDER_KNEE)) + range * (vec3(1.0) - exp(-excess / range));
+}
+
 void main()
 {
-	vec3 col = clamp(pow(f_color.rgb, vec3(2.2)),0, 1);
+	vec3 col = sky_shoulder(pow(max(f_color.rgb, vec3(0.0)), vec3(2.2)));
 #if POSTFX_ENABLED
 	out_color = vec4(apply_fog(col), 1.0f);
 #else