如何在已經繪制的 canvas 上繪制 bitmap

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)
}

在這里，我試圖在從 Surface 創建的 canvas 上繪制位圖（水印）。 但是位圖（水印）在從 Surface 創建的 canvas 下方繪制

Answer 1

發生這種情況是因為您首先繪制 bitmap 和框架。 通過切換繪圖順序，您應該會看到水印

    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)
    }