void dispose()

Call the dispose method to release memory allocated by WebGL.

Source 

void dispose() {

  if (_renderTexture != null) _renderTexture.dispose();
  if (_renderStencilBuffer != null) _renderStencilBuffer.dispose();
  if (_framebuffer != null) _renderingContext.deleteFramebuffer(_framebuffer);

  _contextIdentifier = -1;
  _renderTexture = null;
  _renderStencilBuffer = null;
  _framebuffer = null;
}