Cycles ShaderNetworkAlgo : Remove custom unnormalized light support

Instead rely on Cycles' inbuilt support

Changes.md

@@ -28,12 +28,14 @@ Fixes
 - RenderPassEditor :
   - Fixed history window to update on context changes, for example, when the current frame is changed.
   - Fixed invalid `scene:path` context variables created by the history window. [^1]
+- Cycles : Fixed issue where scaling unnormalized quad and disk lights would not affect their brightness.
 
 Breaking Changes
 ----------------
 
 - IECoreArnold : Added `messageContext` argument to `NodeAlgo::Converter` and `NodeAlgo::MotionConverter`.
 - Instancer : Renamed `encapsulateInstanceGroups` plug to `encapsulate`. Encapsulation now produces a single capsule at the `.../instances` location, instead of capsules at each `.../instances/<prototypeName>` location.
+- Cycles : Removed custom handling of unnormalized lights. We now rely on Cycles' inbuilt behaviour which results in a brightness difference for unnormalized point, spot and disk lights.
 
 [^1]: To be omitted from 1.5.0.0 release notes.
 

src/GafferCycles/IECoreCyclesPreview/ShaderNetworkAlgo.cpp

@@ -356,15 +356,13 @@ T parameterValue( const IECore::CompoundDataMap &parameters, const IECore::Inter
 
 // Cycles lights just have a single `strength` parameter which
 // we want to present as separate "virtual" parameters for
-// intensity, color, exposure and normalize. We calculate un-normalized
-// lights by multiplying the surface area of the light source.
+// intensity, color, exposure.
 bool contributesToLightStrength( InternedString parameterName )
 {
 	return
 		parameterName == "intensity" ||
 		parameterName == "color" ||
-		parameterName == "exposure" ||
-		parameterName == "normalize"
+		parameterName == "exposure"
 	;
 }
 
@@ -387,48 +385,6 @@ Imath::Color3f constantLightStrength( const IECoreScene::ShaderNetwork *light )
 	// you'd want to texture that.
 	strength *= powf( 2.0f, parameterValue<float>( lightShader->parameters(), "exposure", 0.0f ) );
 
-	// Cycles has normalized lights as a default, we can emulate un-normalized lights
-	// with a bit of surface area size calculation onto the strength parameter.
-	/// \todo I think we should move normalization into Cycles itself -
-	/// https://developer.blender.org/D16838
-	if( !parameterValue<bool>( lightShader->parameters(), "normalize", true ) )
-	{
-		if( lightShader->getName() == "distant_light" )
-		{
-			const float angle = IECore::degreesToRadians( parameterValue<float>( lightShader->parameters(), "angle", 0.0f ) ) / 2.0f;
-			const float radius = tanf( angle );
-			const float area = M_PI_F * radius * radius;
-			if( area > 0.0f )
-			{
-				strength *= area;
-			}
-		}
-		else if( lightShader->getName() == "background_light" )
-		{
-			// Do nothing.
-		}
-		else if(
-			lightShader->getName() == "quad_light" ||
-			lightShader->getName() == "portal"
-		)
-		{
-			const float width = parameterValue( lightShader->parameters(), "width", 1.0f );
-			const float height = parameterValue( lightShader->parameters(), "height", 1.0f );
-			strength *= width * height;
-		}
-		else if( lightShader->getName() == "disk_light" )
-		{
-			const float width = parameterValue( lightShader->parameters(), "width", 2.0f ) * 0.5f;
-			const float height = parameterValue( lightShader->parameters(), "height", 2.0f ) * 0.5f;
-			strength *= M_PI * width * height;
-		}
-		else // Point or spot light.
-		{
-			const float size = parameterValue( lightShader->parameters(), "size", 1.0f ) * 0.5f;
-			strength *= M_PI * size * size * 4.0f;
-		}
-	}
-
 	return strength;;
 }