Core: Enable blending when Material.blending is not set to NormalBlending (#23416)

* don't render as opaque if CustomBlending is enabled

* Add CustomBlending import

* add forgetten line

* Update "opaque" condition

src/renderers/webgl/WebGLProgram.js

@@ -674,7 +674,7 @@ function WebGLProgram( renderer, cacheKey, parameters, bindingStates ) {
 			( parameters.toneMapping !== NoToneMapping ) ? getToneMappingFunction( 'toneMapping', parameters.toneMapping ) : '',
 
 			parameters.dithering ? '#define DITHERING' : '',
-			parameters.transparent ? '' : '#define OPAQUE',
+			parameters.opaque ? '#define OPAQUE' : '',
 
 			ShaderChunk[ 'encodings_pars_fragment' ], // this code is required here because it is used by the various encoding/decoding function defined below
 			getTexelEncodingFunction( 'linearToOutputTexel', parameters.outputEncoding ),

src/renderers/webgl/WebGLPrograms.js

@@ -1,4 +1,4 @@
-import { BackSide, DoubleSide, CubeUVRefractionMapping, CubeUVReflectionMapping, ObjectSpaceNormalMap, TangentSpaceNormalMap, NoToneMapping, LinearEncoding, sRGBEncoding } from '../../constants.js';
+import { BackSide, DoubleSide, CubeUVRefractionMapping, CubeUVReflectionMapping, ObjectSpaceNormalMap, TangentSpaceNormalMap, NoToneMapping, LinearEncoding, sRGBEncoding, NormalBlending } from '../../constants.js';
 import { Layers } from '../../core/Layers.js';
 import { WebGLProgram } from './WebGLProgram.js';
 import { WebGLShaderCache } from './WebGLShaderCache.js';
@@ -177,7 +177,7 @@ function WebGLPrograms( renderer, cubemaps, cubeuvmaps, extensions, capabilities
 			specularIntensityMap: !! material.specularIntensityMap,
 			specularColorMap: !! material.specularColorMap,
 
-			transparent: material.transparent,
+			opaque: material.transparent === false && material.blending === NormalBlending,
 
 			alphaMap: !! material.alphaMap,
 			alphaTest: useAlphaTest,
@@ -447,7 +447,7 @@ function WebGLPrograms( renderer, cubemaps, cubeuvmaps, extensions, capabilities
 			_programLayers.enable( 21 );
 		if ( parameters.decodeVideoTexture )
 			_programLayers.enable( 22 );
-		if ( parameters.transparent )
+		if ( parameters.opaque )
 			_programLayers.enable( 23 );
 
 		array.push( _programLayers.mask );