anchor.diff:  
       ImageElement image = document.createElement("img");
       image.onLoad.listen((event){
  +      if (image.width == 0 || image.height == 0) {
  +        return;
  +      }
  +
         bool isPowerOfTwo(int x) => (x & (x - 1)) == 0x00;
         int nextHighestPowerOfTwo(int x) {
           --x;
  
positive.code:     gl.texParameteri(GL.TEXTURE_2D, GL.TEXTURE_MAG_FILTER, GL.LINEAR);
      gl.texImage2DCanvas(GL.TEXTURE_2D, 0, this.internal_format, this.format, this.type, this.canvas);
      gl.bindTexture(GL.TEXTURE_2D, null);
    }
  
    void refresh(GL.RenderingContext gl) {
  
negative.code:         this.canvas.height = nextHighestPowerOfTwo(image.height);
        }
  
        this.ctx.drawImageScaled(image, 0, 0, this.canvas.width, this.canvas.height);
        this.refresh(gl);
        completer.complete(this);
      });
  