android - 为什么我在 Canvas 上的位图出现在背景可绘制对象下方？

Question

我有一个 SurfaceView，我在其中设置背景颜色和图像，如下所示:

BitmapDrawable tiledBackground = new BitmapDrawable(BitmapFactory.decodeResource(getResources(), R.drawable.background));
tiledBackground.setTileModeX(Shader.TileMode.REPEAT);
tiledBackground.setColorFilter(0xaacceeff, PorterDuff.Mode.DST_OVER);
this.setBackgroundDrawable(tiledBackground);

我还有一个动画线程，我在其中绘制图像(连续调整其 x 坐标，使其看起来向左移动)。背景图像是透明的 PNG，因此它的某些部分是透明的。看来我从线程中绘制的图像出现在SurfaceView 上可绘制的背景下方。我怎样才能让它出现在背景之上？我正在这样绘制图像:

private void doDraw(Canvas canvas) {
    canvas.drawColor(Color.BLACK);
    canvas.drawBitmap(missile, x, getHeight() - 95, paint);
    canvas.restore();
}

missile 和 paint 在线程的构造函数中被初始化为:

missile = Bitmap.createBitmap(BitmapFactory.decodeResource(getResources(), R.drawable.missile));
paint = new Paint();

Answer 1

每次调用 doDraw 都应该绘制您想要显示的所有内容，包括背景。

// Add to initializer
tiledBackground = new BitmapDrawable(BitmapFactory.decodeResource(getResources(), R.drawable.background));
tiledBackground.setTileModeX(Shader.TileMode.REPEAT);
tiledBackground.setColorFilter(0xaacceeff, PorterDuff.Mode.DST_OVER);

private void doDraw(Canvas canvas) {
    canvas.drawColor(Color.BLACK);
    // Create a rectangle (just holds top/bottom/left/right info)
    Rect drawRect = new Rect(); 

    // Populate the rectangle that we just created with the drawing area of the canvas.
    canvas.getClipBounds(drawRect);

    // Make the height of the background drawing area equal to the height of the background bitmap
    drawRect.bottom = drawRect.top + tiledBackground.getBitmap().getHeight();

    // Set the drawing area for the background.
    tiledBackground.setBounds(drawRect);

    tiledBackground.draw(canvas);
    canvas.drawBitmap(missile, x, getHeight() - 95, paint);
    canvas.restore();
}