Consolidate diffuse modulation for shading.

Previously, diffuse modulation was applied only to the diffuse lighting terms
while other shading paths—such as self-illumination, night vision,
and Phong-based effects—continued to use the unmodulated base color.
This led to inconsistent material appearance and visual artifacts
when per-instance color overrides (e.g., rendercolor or proxy-driven modulation) were used.

This change applies diffuse modulation to the base color itself before
any shading calculations, ensuring that all subsequent lighting and shading paths
operate on the fully modulated color. The visual output is now consistent,
and the shader behavior aligns with the intended use of diffuse modulation
as a persistent per-instance color modification.

Author: Kitsune44

src/materialsystem/stdshaders/character_ps20b.fxc

@@ -211,6 +211,9 @@ float4 main( PS_INPUT i ) : COLOR
 	baseColor.xyz = lerp(baseColor.xyz, hsv2rgb(baseColorHSV), saturate(baseColor.a + g_fInverseBlendTintByBaseAlpha));
 #endif
 
+	// Optionally use basealpha to blend in the diffuse modulation (saturated add of g_fInverseBlendTintByBaseAlpha turns this on/off)
+    baseColor.rgb *= lerp(float3(1.0f, 1.0f, 1.0f), g_DiffuseModulation.rgb, saturate(baseColor.a + g_fInverseBlendTintByBaseAlpha));
+
 	float flWrinkleAmount, flStretchAmount, flTextureAmount;
 	#if ( WRINKLEMAP )
 	{
@@ -326,7 +329,6 @@ float4 main( PS_INPUT i ) : COLOR
 	}		
 	#endif	
 
-	float3 albedo = baseColor.rgb;
 
 	float3 specularLighting = float3( 0.0f, 0.0f, 0.0f );
 	float3 rimLighting = float3( 0.0f, 0.0f, 0.0f );
@@ -383,10 +385,7 @@ float4 main( PS_INPUT i ) : COLOR
 	}
 	#endif	
 
-	// Optionally use basealpha to blend in the diffuse modulation (saturated add of g_fInverseBlendTintByBaseAlpha turns this on/off)
-	diffuseLighting *= lerp( float3( 1.0f, 1.0f, 1.0f ), g_DiffuseModulation.rgb, saturate( baseColor.a + g_fInverseBlendTintByBaseAlpha ) );
-
-	float3 diffuseComponent = albedo * diffuseLighting;
+    float3 diffuseComponent = baseColor.rgb * diffuseLighting;
 
 	#if ( SELFILLUM && !FLASHLIGHT )
 	{
@@ -397,13 +396,13 @@ float4 main( PS_INPUT i ) : COLOR
 			float3 vSelfIllumMask = tex2D( SelfIllumMaskSampler, i.baseTexCoordDetailTexCoord.xy );
 			vSelfIllumMask = lerp( baseColor.aaa, vSelfIllumMask, g_SelfIllumMaskControl );
 			float flSelfIllumFresnel = ( pow( saturate( dot( vVertexNormal.xyz, vEyeDir.xyz ) ), g_SelfIllumScaleBiasExpBrightness.z ) * g_SelfIllumScaleBiasExpBrightness.x ) + g_SelfIllumScaleBiasExpBrightness.y;
-			diffuseComponent = lerp( diffuseComponent, g_SelfIllumTint_and_DetailBlendFactor.rgb * albedo * g_SelfIllumScaleBiasExpBrightness.w, vSelfIllumMask.rgb * saturate( flSelfIllumFresnel ) );
+			diffuseComponent = lerp( diffuseComponent, g_SelfIllumTint_and_DetailBlendFactor.rgb * baseColor.rgb * g_SelfIllumScaleBiasExpBrightness.w, vSelfIllumMask.rgb * saturate( flSelfIllumFresnel ) );
 		}
 		#else
 		{
 			float3 vSelfIllumMask = tex2D( SelfIllumMaskSampler, i.baseTexCoordDetailTexCoord.xy );
 			vSelfIllumMask = lerp( baseColor.aaa, vSelfIllumMask, g_SelfIllumMaskControl );
-			diffuseComponent = lerp( diffuseComponent, g_SelfIllumTint_and_DetailBlendFactor.rgb * albedo, vSelfIllumMask );
+			diffuseComponent = lerp( diffuseComponent, g_SelfIllumTint_and_DetailBlendFactor.rgb * baseColor.rgb, vSelfIllumMask );
 		}
 		#endif
 
@@ -415,11 +414,11 @@ float4 main( PS_INPUT i ) : COLOR
 	{
 		if ( g_fNightVisionAmount < 1.0 )
 		{
-			diffuseComponent = lerp( diffuseComponent, albedo, g_fNightVisionAmount );
+			diffuseComponent = lerp( diffuseComponent, baseColor.rgb, g_fNightVisionAmount );
 		}
 		else
 		{
-			diffuseComponent = albedo * g_fNightVisionAmount;
+			diffuseComponent = baseColor.rgb * g_fNightVisionAmount;
 		}
 	}
 	#endif