Renderers: Remove premultipliedAlpha requirement for MultiplyBlending/SubtractiveBlending.

src/renderers/webgl-fallback/utils/WebGLState.js

@@ -377,11 +377,11 @@ class WebGLState {
 							break;
 
 						case SubtractiveBlending:
-							error( 'WebGLState: SubtractiveBlending requires material.premultipliedAlpha = true' );
+							gl.blendFuncSeparate( gl.ZERO, gl.ONE_MINUS_SRC_COLOR, gl.ZERO, gl.ONE );
 							break;
 
 						case MultiplyBlending:
-							error( 'WebGLState: MultiplyBlending requires material.premultipliedAlpha = true' );
+							gl.blendFuncSeparate( gl.DST_COLOR, gl.ONE_MINUS_SRC_ALPHA, gl.ZERO, gl.ONE );
 							break;
 
 						default:

src/renderers/webgl/WebGLState.js

@@ -690,11 +690,11 @@ function WebGLState( gl, extensions ) {
 							break;
 
 						case SubtractiveBlending:
-							error( 'WebGLState: SubtractiveBlending requires material.premultipliedAlpha = true' );
+							gl.blendFuncSeparate( gl.ZERO, gl.ONE_MINUS_SRC_COLOR, gl.ZERO, gl.ONE );
 							break;
 
 						case MultiplyBlending:
-							error( 'WebGLState: MultiplyBlending requires material.premultipliedAlpha = true' );
+							gl.blendFuncSeparate( gl.DST_COLOR, gl.ONE_MINUS_SRC_ALPHA, gl.ZERO, gl.ONE );
 							break;
 
 						default:

src/renderers/webgpu/utils/WebGPUPipelineUtils.js

@@ -448,11 +448,11 @@ class WebGPUPipelineUtils {
 						break;
 
 					case SubtractiveBlending:
-						error( 'WebGPURenderer: SubtractiveBlending requires material.premultipliedAlpha = true' );
+						setBlend( GPUBlendFactor.Zero, GPUBlendFactor.OneMinusSrc, GPUBlendFactor.Zero, GPUBlendFactor.One );
 						break;
 
 					case MultiplyBlending:
-						error( 'WebGPURenderer: MultiplyBlending requires material.premultipliedAlpha = true' );
+						setBlend( GPUBlendFactor.Dst, GPUBlendFactor.OneMinusSrcAlpha, GPUBlendFactor.Zero, GPUBlendFactor.One );
 						break;
 
 				}