Align REFRACTION_TWO_SIDED in GLSL and MSL rendering (#2703)

ld-kerley · web-flow · commit f611f6d8341f · 2025-12-01T15:24:22.000-08:00
While investigating render differences between GLSL and MSL in #2697 I noticed the dielectric transmission case wasn't matching. After a little investigation it appears that in the MSL render module we're missing setting `HW::REFRACTION_TWO_SIDED `. Which causes a different path to be taken through the shader code [here](https://github.com/AcademySoftwareFoundation/MaterialX/blob/main/libraries/pbrlib/genglsl/lib/mx_transmission_refract.glsl#L9). If more differences appear like this, it may be worth investigating a `MaterialXRenderHW` module to encapsulate the common code.
diff --git a/source/MaterialXRenderMsl/MslPipelineStateObject.mm b/source/MaterialXRenderMsl/MslPipelineStateObject.mm
@@ -741,6 +741,7 @@ int GetStrideOfMetalType(MTLDataType type)
             }
         }
     }
+    bindUniform(HW::REFRACTION_TWO_SIDED, Value::createValue(lightHandler->getRefractionTwoSided()), false);
 
     // Bind direct lighting properties.
     if (hasUniform(HW::NUM_ACTIVE_LIGHT_SOURCES))

Original file line number	Diff line number	Diff line change
`@@ -741,6 +741,7 @@ int GetStrideOfMetalType(MTLDataType type)`
`741`	`741`	`}`
`742`	`742`	`}`
`743`	`743`	`}`
	`744`	`+ bindUniform(HW::REFRACTION_TWO_SIDED, Value::createValue(lightHandler->getRefractionTwoSided()), false);`
`744`	`745`
`745`	`746`	`// Bind direct lighting properties.`
`746`	`747`	`if (hasUniform(HW::NUM_ACTIVE_LIGHT_SOURCES))`