copy method
Implementation
@override
WebGLMultipleRenderTargets copy(WebGLRenderTarget source) {
dispose();
width = source.width;
height = source.height;
depth = source.depth;
viewport.set(0, 0, width, height);
scissor.set(0, 0, width, height);
depthBuffer = source.depthBuffer;
stencilBuffer = source.stencilBuffer;
if ( source.depthTexture != null ) {
depthTexture = source.depthTexture!.clone();
}
texture.length = 0;
for (var i = 0, il = source.texture.length; i < il; i++) {
texture[i] = source.texture[i].clone();
}
return this;
}