GLTF Viewer: use proper opacity when applying post effects

Author: TheMostDiligent

Samples/GLTFViewer/assets/shaders/ApplyPostEffects.psh

@@ -49,9 +49,10 @@ float4 main(in FullScreenTriangleVSOutput VSOut) : SV_Target
 
     float3 SSR = GetSpecularIBL_GGX(SrfInfo, IBLInfo, SSRRadiance.rgb);
 
+    float Opacity = 1.0 - OutColor.a;
     if (DebugMode == 0.0)
     {
-        OutColor.rgb += (SSR.rgb - SpecularIBL.rgb) * SSRRadiance.w * OutColor.a * SSRScale;
+        OutColor.rgb += (SSR.rgb - SpecularIBL.rgb) * SSRRadiance.w * Opacity * SSRScale;
     }
     else if (DebugMode == 1.0)
     {

Samples/GLTFViewer/src/GLTFViewer.cpp

@@ -1321,9 +1321,7 @@ void GLTFViewer::Render()
         EnvMapAttribs.pEnvMap       = pEnvMapSRV;
         EnvMapAttribs.AverageLogLum = m_ShaderAttribs.AverageLogLum;
         EnvMapAttribs.MipLevel      = m_EnvMapMipLevel;
-        // It is essential to write zero alpha because we use alpha channel
-        // to attenuate SSR for transparent surfaces.
-        EnvMapAttribs.Alpha = 0.0;
+        EnvMapAttribs.Alpha         = 1.0;
         if ((m_RenderParams.Flags & GLTF_PBR_Renderer::PSO_FLAG_CONVERT_OUTPUT_TO_SRGB) != 0)
             EnvMapAttribs.Options |= EnvMapRenderer::OPTION_FLAG_CONVERT_OUTPUT_TO_SRGB;
         if (m_bEnablePostProcessing)