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我有一个正在绘制场景的 SurfaceView 画布。画布被转换以适应 1024x768 的逻辑场景大小（而实际屏幕为 800x480），并且还支持缩放/滚动导航。因为我不想在侧面出现黑色条纹（适合 4:3 到 16:9），所以我使用了不同的背景位图，它具有“拉伸”的侧面来覆盖比率差异。情节的另一个转折是我需要同时支持电话和桌子。对于平板电脑，我正在加载更高质量（尺寸）的图像，对于手机，我在从磁盘加载时缩小背景位图。下面是执行我想要的代码（尽管可能不是最好的方法），特别是，我感觉背景计算可以缓存到矩阵中以供以后使用canvas.drawBitmap(Bitmap, Matrix, Paint);

（此外，我无法通过使用这些偏移量翻译画布来获得 drawBitmap(Bitmap, left, top, Paint) 的等效定位，我也很好奇为什么）。

这是绘制例程：

public void draw(Canvas canvas) {    
    canvas.save();
    float midX = width/2;
    float midY = height/2;

    // zoom out to fit logical view, and translate for future
    // sprite drawing with logical coordinates
    // x,y and zoom are calculated in on init and updated in touch events
    canvas.translate(x, y);
    canvas.scale(zoom, zoom, midX, midY);

    // background part
    if(back != null && !back.isRecycled()) {
        // todo: these can probably be pre-calculated for optimization
        // todo: but so far I couldn't get it right..
        if(bgMatrix != null) { // this is where I'm thinking of using the cached matrix
            canvas.drawBitmap(back, bgMatrix, paint);
        }
        else {
           float offsetW = (width-back.getWidth())/2;
           float offsetH = (height-back.getHeight())/2;

           canvas.save();
           // bgScaleFactor is calculated upon setting the bg bitmap
           // it says by how much we need to scale the image to fill the canvas
           // taking into account the image (possible) downscale 
           canvas.scale(bgScaleFactor, bgScaleFactor, midX, midY);
           // this doesn't work: canvas.postTranslate(offsetW, offsetH) and use 0,0 for next draw
           canvas.drawBitmap(back, offsetW, offsetH, paint);
           // todo: here I would like to save a matrix which represents
           // how the back bitmap was drawn onto the canvas
           // so that next time these calculations can be avoided
           // this fails: bgMatrix = canvas.getMatrix();
           canvas.restore();
    }

    // draw scene shapes on transformed canvas
    if(shapes != null){
    shapes.onDraw(canvas);
}

canvas.restore();
}
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