Tutorial 29: do not use alpha for opaque objects

DiligentGraphics · Jan 4, 2025 · ca06208 · ca06208
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Showing 3 changed files with 13 additions and 4 deletions.
diff --git a/Tutorials/Tutorial29_OIT/assets/alpha_blend.psh b/Tutorials/Tutorial29_OIT/assets/alpha_blend.psh
@@ -15,8 +15,17 @@ void main(in PSInput   PSIn,
 {
     float4 Color;
     Color.rgb = ComputeLighting(PSIn.Color.rgb, PSIn.Normal, g_Constants.LightDir.xyz);
-    Color.a   = lerp(g_Constants.MinOpacity, g_Constants.MaxOpacity, PSIn.Color.a);
-    Color.rgb *= Color.a;
+    if (PSIn.Color.a < 0.0)
+    {
+        // Opaque
+        Color.a = 1.0;
+    }
+    else
+    {
+        // Transparent
+        Color.a = lerp(g_Constants.MinOpacity, g_Constants.MaxOpacity, PSIn.Color.a);
+        Color.rgb *= Color.a;
+    }
 
 #if CONVERT_PS_OUTPUT_TO_GAMMA
     // Use fast approximation for gamma correction.

diff --git a/Tutorials/Tutorial29_OIT/src/Tutorial29_OIT.cpp b/Tutorials/Tutorial29_OIT/src/Tutorial29_OIT.cpp
@@ -449,7 +449,7 @@ void Tutorial29_OIT::CreateInstanceBuffers()
         {
             Instance.TranslationAndScale = float4{offset_distr(gen), offset_distr(gen), offset_distr(gen), BaseScale * scale_distr(gen)};
             float4 TransparentColor{color_distr(gen), color_distr(gen), color_distr(gen), alpha_distr(gen)};
-            float4 OpaqueColor{0.5, 0.5, 0.5, 1.0};
+            float4 OpaqueColor{0.5, 0.5, 0.5, -1.0};
             Instance.Color = IsTransparent ? TransparentColor : OpaqueColor;
         }
         // Update instance data buffer

diff --git a/Tutorials/Tutorial29_OIT/src/Tutorial29_OIT.hpp b/Tutorials/Tutorial29_OIT/src/Tutorial29_OIT.hpp
@@ -99,7 +99,7 @@ class Tutorial29_OIT final : public SampleBase
     float4x4              m_ProjMatrix;
     float4x4              m_ViewProjMatrix;
     int                   m_GridSize          = 10;
-    float                 m_PercentOpaque     = 25;
+    float                 m_PercentOpaque     = 10;
     float                 m_MinOpacity        = 0.2f;
     float                 m_MaxOpacity        = 1.0f;
     Uint32                m_ThreadGroupSizeXY = 16;