Disable writing to alpha with opaque framebuffer

drivers/gles2/rasterizer_scene_gles2.cpp

@@ -2392,7 +2392,7 @@ void RasterizerSceneGLES2::_render_render_list(RenderList::Element **p_elements,
 						if (storage->frame.current_rt && storage->frame.current_rt->flags[RasterizerStorage::RENDER_TARGET_TRANSPARENT]) {
 							glBlendFuncSeparate(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
 						} else {
-							glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+							glBlendFuncSeparate(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ZERO, GL_ONE);
 						}
 
 					} break;

drivers/gles3/rasterizer_scene_gles3.cpp

@@ -2102,7 +2102,7 @@ void RasterizerSceneGLES3::_render_list(RenderList::Element **p_elements, int p_
 							if (storage->frame.current_rt && storage->frame.current_rt->flags[RasterizerStorage::RENDER_TARGET_TRANSPARENT]) {
 								glBlendFuncSeparate(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
 							} else {
-								glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+								glBlendFuncSeparate(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ZERO, GL_ONE);
 							}
 
 						} break;
@@ -4461,7 +4461,7 @@ void RasterizerSceneGLES3::render_scene(const Transform &p_cam_transform, const
 		glBlendFuncSeparate(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
 		glEnable(GL_BLEND);
 	} else {
-		glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+		glBlendFuncSeparate(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ZERO, GL_ONE);
 		glDisable(GL_BLEND);
 	}