code: func (gf *GLFrame) Color(at pixel.Vec) pixel.RGBA {
  	if gf.dirty {
  		mainthread.Call(func() {
  			tex := gf.frame.Texture()
  			tex.Begin()
  			gf.pixels = tex.Pixels(0, 0, tex.Width(), tex.Height())
  			tex.End()
  		})
  		gf.dirty = false
  	}
  	if !gf.bounds.Contains(at) {
  		return pixel.Alpha(0)
  	}
  	bx, by, bw, _ := intBounds(gf.bounds)
  	x, y := int(at.X)-bx, int(at.Y)-by
  	off := y*bw + x
  	return pixel.RGBA{
  		R: float64(gf.pixels[off*4+0]) / 255,
  		G: float64(gf.pixels[off*4+1]) / 255,
  		B: float64(gf.pixels[off*4+2]) / 255,
  		A: float64(gf.pixels[off*4+3]) / 255,
  	}
  }
docs: // Color returns the color of the pixel under the specified position.