1. @DomName('WebGLRenderingContext.copyTexSubImage2D')
  2. @DocsEditable()
void copyTexSubImage2D(int target, int level, int xoffset, int yoffset, int x, int y, int width, int height)

Source 

@DomName('WebGLRenderingContext.copyTexSubImage2D')
@DocsEditable()
void copyTexSubImage2D(int target, int level, int xoffset, int yoffset, int x,
        int y, int width, int height) =>
    _blink.BlinkWebGLRenderingContext.instance.copyTexSubImage2D_Callback_8_(
        this, target, level, xoffset, yoffset, x, y, width, height);