java - 与 Bitmap.Config.ALPHA_8 的像素完美碰撞

Question

我找到了这段像素完美碰撞检查代码，并在我的代码中使用了它:

public boolean isCollisionDetected(
    Bitmap bitmap1, int x1, int y1,
    Bitmap bitmap2, int x2, int y2
) {
    Rect bounds1 = new Rect(
        x1, y1, x1 + bitmap1.getWidth(), y1 + bitmap1.getHeight()
    );
    Rect bounds2 = new Rect(
        x2, y2, x2 + bitmap2.getWidth(), y2 + bitmap2.getHeight()
    );

    if (Rect.intersects(bounds1, bounds2)) {
        Rect collisionBounds = getCollisionBounds(bounds1, bounds2);
        for (int i = collisionBounds.left; i < collisionBounds.right; i++) {
            for (int j = collisionBounds.top; j < collisionBounds.bottom; j++) {
                int bitmap1Pixel = bitmap1.getPixel(i - x1, j - y1);
                int bitmap2Pixel = bitmap2.getPixel(i - x2, j - y2);
                if (isFilled(bitmap1Pixel) && isFilled(bitmap2Pixel)) {
                    return true;
                }
            }
        }
    }
    return false;
}

private Rect getCollisionBounds(Rect rect1, Rect rect2) {
    int left = (int) Math.max(rect1.left, rect2.left);
    int top = (int) Math.max(rect1.top, rect2.top);
    int right = (int) Math.min(rect1.right, rect2.right);
    int bottom = (int) Math.min(rect1.bottom, rect2.bottom);
    return new Rect(left, top, right, bottom);
}

private boolean isFilled(int pixel) {
    return pixel != Color.TRANSPARENT;
}

而且它运行完美，从来没有出现过任何问题。直到我将图像设置为 Bitmap.Config.ALPHA_8使用此代码(由于 RAM 问题):

private Bitmap convert(Bitmap bitmap, Bitmap.Config config) {
    Bitmap convertedBitmap = 
        Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), config);
    Canvas canvas = new Canvas(convertedBitmap);
    Paint paint = new Paint();
    paint.setColor(Color.BLACK);
    canvas.drawBitmap(bitmap, 0, 0, paint);
    return convertedBitmap;
}

为什么什么都不会发生，它确实在 isCollisionDetected 中，我已经检查过日志!但它不会检测碰撞...任何人都可以提供检查位图与 Bitmap.Config.ALPHA_8 像素完美碰撞的工作功能吗？

Answer 1

调用 getPixel()在具有 ALPHA_8 配置的位图上将始终返回零。这似乎是a bug .

您可以通过将每个位图的像素存储为字节数组来解决此问题:

byte[] pixelData = getPixels(convert(bitmap, Bitmap.Config.ALPHA_8));

...

public byte[] getPixels(Bitmap bmp) {
    int bytes = bmp.getRowBytes() * bmp.getHeight();
    ByteBuffer buffer = ByteBuffer.allocate(bytes);
    bmp.copyPixelsToBuffer(buffer);
    return buffer.array();
}

您需要稍微修改一下碰撞检测函数:

public boolean isCollisionDetected(
    byte[] pixels1, Bitmap bitmap1, int x1, int y1,
    byte[] pixels2, Bitmap bitmap2, int x2, int y2
) {
    Rect bounds1 = new Rect(
        x1, y1, x1 + bitmap1.getWidth(), y1 + bitmap1.getHeight()
    );
    Rect bounds2 = new Rect(
        x2, y2, x2 + bitmap2.getWidth(), y2 + bitmap2.getHeight()
    );

    if (Rect.intersects(bounds1, bounds2)) {
        Rect collisionBounds = getCollisionBounds(bounds1, bounds2);
        for (int i = collisionBounds.left; i < collisionBounds.right; i++) {
            for (int j = collisionBounds.top; j < collisionBounds.bottom; j++) {
                byte bitmap1Pixel = pixels1[((j - y1) * width1) + (i - x1)];
                byte bitmap2Pixel = pixels2[((j - y2) * width2) + (i - x2)];
                if (isFilled(bitmap1Pixel) && isFilled(bitmap2Pixel)) {
                    return true;
                }
            }
        }
    }
    return false;
}