copy method 
    
    
    
  Implementation
  RenderTarget copy(RenderTarget source){
		height = source.height;
  width = source.width;
		depth = source.depth;
		scissor.setFrom( source.scissor );
		scissorTest = source.scissorTest;
		viewport.setFrom( source.viewport );
		textures.length = 0;
		for (int i = 0, il = source.textures.length; i < il; i ++ ) {
			textures.add(source.textures[ i ].clone());
			textures[ i ].isRenderTargetTexture = true;
		}
		// ensure image object is not shared, see #20328
		final image = source.texture.image;
		texture.source = Source( image );
		depthBuffer = source.depthBuffer;
		stencilBuffer = source.stencilBuffer;
		resolveDepthBuffer = source.resolveDepthBuffer;
		resolveStencilBuffer = source.resolveStencilBuffer;
		if ( source.depthTexture != null ) depthTexture = source.depthTexture!.clone();
		samples = source.samples;
		return this;
}