code: func NewContextForRGBA(im *image.RGBA) *Context {
  	w := im.Bounds().Size().X
  	h := im.Bounds().Size().Y
  	return &Context{
  		width:         w,
  		height:        h,
  		rasterizer:    raster.NewRasterizer(w, h),
  		im:            im,
  		color:         color.Transparent,
  		fillPattern:   defaultFillStyle,
  		strokePattern: defaultStrokeStyle,
  		lineWidth:     1,
  		fillRule:      FillRuleWinding,
  		fontFace:      basicfont.Face7x13,
  		fontHeight:    13,
  		matrix:        Identity(),
  	}
  }
docs: // NewContextForRGBA prepares a context for rendering onto the specified image.
  // No copy is made.