Golang Image.SubImage方法代碼示例

// drawPencil takes an (x, y) position (from a MotionNotify event) and draws
// a rectangle of size pencilTip on to canvas.
func drawPencil(canvas *xgraphics.Image, win *xwindow.Window, x, y int) {
	// Create a subimage at (x, y) with pencilTip width and height from canvas.
	// Creating subimages is very cheap---no pixels are copied.
	// Moreover, when subimages are drawn to the screen, only the pixels in
	// the sub-image are sent to X.
	tipRect := midRect(x, y, pencilTip, pencilTip, width, height)

	// If the rectangle contains no pixels, don't draw anything.
	if tipRect.Empty() {
		return
	}

	// Output a little message.
	log.Printf("Drawing pencil point at (%d, %d)", x, y)

	// Create the subimage of the canvas to draw to.
	tip := canvas.SubImage(tipRect)
	fmt.Println(tip.Rect)

	// Now color each pixel in tip with the pencil color.
	tip.For(func(x, y int) xgraphics.BGRA {
		return xgraphics.BlendBGRA(tip.At(x, y).(xgraphics.BGRA), pencil)
	})

	// Now draw the changes to the pixmap.
	tip.XDraw()

	// And paint them to the window.
	tip.XPaint(win.Id)
}

// drawGopher draws the gopher image to the canvas.
func drawGopher(canvas *xgraphics.Image, gopher image.Image,
	win *xwindow.Window, x, y int) {

	// Find the rectangle of the canvas where we're going to draw the gopher.
	gopherRect := midRect(x, y, gopherWidth, gopherHeight, width, height)

	// If the rectangle contains no pixels, don't draw anything.
	if gopherRect.Empty() {
		return
	}

	// Output a little message.
	log.Printf("Drawing gopher at (%d, %d)", x, y)

	// Get a subimage of the gopher that's in sync with gopherRect.
	gopherPt := image.Pt(gopher.Bounds().Min.X, gopher.Bounds().Min.Y)
	if gopherRect.Min.X == 0 {
		gopherPt.X = gopherWidth - gopherRect.Dx()
	}
	if gopherRect.Min.Y == 0 {
		gopherPt.Y = gopherHeight - gopherRect.Dy()
	}

	// Create the canvas subimage.
	subCanvas := canvas.SubImage(gopherRect)

	// Blend the gopher image into the sub-canvas.
	// This does alpha blending.
	xgraphics.Blend(subCanvas, gopher, gopherPt)

	// Now draw the changes to the pixmap.
	subCanvas.XDraw()

	// And paint them to the window.
	subCanvas.XPaint(win.Id)
}