如何在已绘制的位图上绘制位图 canvas

Question

val canvas = inputSurface.lockCanvas(null)
try {
    val source = Rect(200, 200, 400, 400)
    canvas.drawBitmap(watermark, null, source, null)
   currentFrame.draw(canvas)
} finally {
    inputSurface.unlockCanvasAndPost(canvas)
}

这里我试图在从 Surface 创建的 canvas 上绘制位图（水印）。但是位图（水印）绘制在从 Surface

创建的 canvas 下面

Answer 1

发生这种情况是因为您首先绘制位图和框架。 通过切换绘图顺序，您应该会看到水印

    val canvas = inputSurface.lockCanvas(null)
    try {
        //First draw the frame
        currentFrame.draw(canvas)

        val source = Rect(200, 200, 400, 400)
        //Then draw the bitmap watermark
        canvas.drawBitmap(watermark, null, source, null)
    } finally {
        inputSurface.unlockCanvasAndPost(canvas)
    }