Improve skybox

environment/skydome.cpp

@@ -218,7 +218,10 @@ void CSkyDome::RebuildColors() {
 		vertex = glm::normalize( m_vertices[ i ] );
 
 		// angle between sun and vertex
-		const float gamma = std::acos( glm::dot( vertex, m_sundirection ) );
+		// NOTE: the dot product can exceed the [ -1, 1 ] range by a rounding error,
+		// which would turn the vertex - and, through the averages, the fog and ambient
+		// light - into a NaN, so it gets clamped before feeding it to acos()
+		const float gamma = std::acos( std::clamp( glm::dot( vertex, m_sundirection ), -1.0f, 1.0f ) );
 
 		// warning : major hack!!! .. i had to do something with values under horizon
 		//vertex.y = Clamp<float>( vertex.y, 0.05f, 1.0f );

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