add THREE.ReverseSubtractiveBlending

src/materials/Material.js

@@ -9,3 +9,4 @@ THREE.NormalBlending = 0;
 THREE.AdditiveBlending = 1;
 THREE.SubtractiveBlending = 2;
 THREE.BillboardBlending = 3;
+THREE.ReverseSubtractiveBlending=4;

src/renderers/WebGLRenderer.js

@@ -2173,6 +2173,12 @@ THREE.WebGLRenderer = function ( parameters ) {
 
 					break;
 
+				case THREE.ReverseSubtractiveBlending:
+
+					_gl.blendEquation( _gl.FUNC_REVERSE_SUBTRACT );
+					_gl.blendFunc( _gl.ONE, _gl.ONE );
+
+    				break;
 				default:
 
 					_gl.blendEquation( _gl.FUNC_ADD );