Fix computation of alpha channel for transparent objects (#110)

* shaders/PbrTransparent : fix how accumulation and revealage computed in fragment shader

+ weight applies to accum.a, not to revealage (account for change in blend formula)

* Update CHANGELOG

Author: ManifoldFR

CHANGELOG.md

@@ -24,6 +24,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Fixed visual effects with SSAO + MSAA. Have SSAO sample from resolved multisampled depth texture (https://github.com/Simple-Robotics/candlewick/pull/105)
+- Fix WBOIT transparent shader formulas, fixing transparency visual appearance and alpha channel in PNG screenshots (https://github.com/Simple-Robotics/candlewick/pull/110)
 
 ## [0.10.1] - 2026-01-19
 

shaders/compiled/PbrTransparent.frag.msl

@@ -192,7 +192,7 @@ struct KernelContext_0
     float weight_0 = clamp((alpha_0 * 10.0 + 0.00999999977648258) * (1.0 - fragCoord_0.z * 0.30000001192092896), 0.00999999977648258, 1000.0);
 
     thread FSOutput_0 output_0;
-    (&output_0)->accum_0 = float4(pow(uncharted2ToneMapping_0(float3(0.02999999932944775)  * mat_0.baseColor_0.xyz * float3(mat_0.ao_0)  + Lo_0), float3(0.45454543828964233) ) * float3(alpha_0)  * float3(weight_0) , alpha_0);
-    (&output_0)->reveal_0 = 1.0 - alpha_0 * weight_0;
+    (&output_0)->accum_0 = float4(pow(uncharted2ToneMapping_0(float3(0.02999999932944775)  * mat_0.baseColor_0.xyz * float3(mat_0.ao_0)  + Lo_0), float3(0.45454543828964233) ) * float3(alpha_0)  * float3(weight_0) , alpha_0 * weight_0);
+    (&output_0)->reveal_0 = alpha_0;
     return output_0;
 }

shaders/compiled/PbrTransparent.frag.spv

@@ -41,7 +41,7 @@ FSOutput main([vk::location(0)] float3 fragViewPos,
     float weight = clamp(w1 * (1.0 - z * 0.3), 1e-2, 1e3);
 
     FSOutput output;
-    output.accum  = float4(color * alpha * weight, alpha);
-    output.reveal = 1.0 - alpha * weight;
+    output.accum  = float4(color * alpha * weight, alpha * weight);
+    output.reveal = alpha;
     return output;
 }