code: func (dc *Context) MeasureString(s string) (w, h float64) {
  	d := &font.Drawer{
  		Face: dc.fontFace,
  	}
  	a := d.MeasureString(s)
  	return float64(a >> 6), dc.fontHeight
  }
docs: // MeasureString returns the rendered width and height of the specified text
  // given the current font face.