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fix: handle alphaToCoverage in shadow map generation #30760

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fix: handle alphaToCoverage in shadow map generation #30760

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da187b5
fix: handle alphaToCoverage in shadow map generation
mattverse Mar 20, 2025
acc574f
change alphatest value
mattverse Mar 20, 2025
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32 changes: 23 additions & 9 deletions src/renderers/webgl/WebGLShadowMap.js
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Original file line number Diff line number Diff line change
Expand Up @@ -302,17 +302,31 @@ function WebGLShadowMap( renderer, objects, capabilities ) {

}

result.alphaMap = material.alphaMap;
result.alphaTest = material.alphaTest;
result.map = material.map;
if ( customMaterial === undefined ) {
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@Mugen87 Mugen87 Mar 23, 2025 •
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Why did you introduce this new if statement?

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@mattverse mattverse Mar 23, 2025

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Previously, when a user provided customDepthMaterial, the original code overwrote properties like alphaMap or alphaTest of the customMaterial without this if statement

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@Mugen87 Mugen87 Mar 31, 2025

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Do you mind testing this version of getDepthMaterial()? Only two lines need to be changed and the codesandbox works:

function getDepthMaterial( object, material, light, type ) {

	let result = null;

	const customMaterial = ( light.isPointLight === true ) ? object.customDistanceMaterial : object.customDepthMaterial;

	if ( customMaterial !== undefined ) {

		result = customMaterial;

	} else {

		result = ( light.isPointLight === true ) ? _distanceMaterial : _depthMaterial;

		if ( ( renderer.localClippingEnabled && material.clipShadows === true && Array.isArray( material.clippingPlanes ) && material.clippingPlanes.length !== 0 ) ||
			( material.displacementMap && material.displacementScale !== 0 ) ||
			( material.alphaMap && material.alphaTest > 0 ) ||
			( material.map && material.alphaTest > 0 ) ||
			( material.alphaToCoverage === true ) ) {

			// in this case we need a unique material instance reflecting the
			// appropriate state

			const keyA = result.uuid, keyB = material.uuid;

			let materialsForVariant = _materialCache[ keyA ];

			if ( materialsForVariant === undefined ) {

				materialsForVariant = {};
				_materialCache[ keyA ] = materialsForVariant;

			}

			let cachedMaterial = materialsForVariant[ keyB ];

			if ( cachedMaterial === undefined ) {

				cachedMaterial = result.clone();
				materialsForVariant[ keyB ] = cachedMaterial;
				material.addEventListener( 'dispose', onMaterialDispose );

			}

			result = cachedMaterial;

		}

	}

	result.visible = material.visible;
	result.wireframe = material.wireframe;

	if ( type === VSMShadowMap ) {

		result.side = ( material.shadowSide !== null ) ? material.shadowSide : material.side;

	} else {

		result.side = ( material.shadowSide !== null ) ? material.shadowSide : shadowSide[ material.side ];

	}

	result.alphaMap = material.alphaMap;
	result.alphaTest = ( material.alphaToCoverage === true ) ? 0.5 : material.alphaTest;
	result.map = material.map;

	result.clipShadows = material.clipShadows;
	result.clippingPlanes = material.clippingPlanes;
	result.clipIntersection = material.clipIntersection;

	result.displacementMap = material.displacementMap;
	result.displacementScale = material.displacementScale;
	result.displacementBias = material.displacementBias;

	result.wireframeLinewidth = material.wireframeLinewidth;
	result.linewidth = material.linewidth;

	if ( light.isPointLight === true && result.isMeshDistanceMaterial === true ) {

		const materialProperties = renderer.properties.get( result );
		materialProperties.light = light;

	}

	return result;

}

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@Mugen87 Mugen87 Mar 31, 2025 •
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To further explain the issue: alphaToCoverage requires a MSAA context which is not available when rendering shadow maps. The idea is to "emulate" the transparency by setting alphaTest to a fixed value. The resulting shadows should be a good approximation.


result.clipShadows = material.clipShadows;
result.clippingPlanes = material.clippingPlanes;
result.clipIntersection = material.clipIntersection;
result.alphaMap = material.alphaMap;
result.map = material.map;

result.displacementMap = material.displacementMap;
result.displacementScale = material.displacementScale;
result.displacementBias = material.displacementBias;
// Check if the original material uses alphaToCoverage
if ( material.alphaToCoverage ) {

result.alphaTest = 0.5;

} else {

result.alphaTest = material.alphaTest;

}

result.clipShadows = material.clipShadows;
result.clippingPlanes = material.clippingPlanes;
result.clipIntersection = material.clipIntersection;

result.displacementMap = material.displacementMap;
result.displacementScale = material.displacementScale;
result.displacementBias = material.displacementBias;

}

result.wireframeLinewidth = material.wireframeLinewidth;
result.linewidth = material.linewidth;
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