Android -- 触摸Area对焦区域

private Rect calculateTapArea(float x, float y, float coefficient) {
        float focusAreaSize = 300;
        int areaSize = Float.valueOf(focusAreaSize * coefficient).intValue();

        int centerX = (int) (x / getResolution().width - 1000);
        int centerY = (int) (y / getResolution().height - 1000);

        int left = clamp(centerX - areaSize / 2, -1000, 1000);
        int top = clamp(centerY - areaSize / 2, -1000, 1000);

        RectF rectF = new RectF(left, top, left + areaSize, top + areaSize);

        return new Rect(Math.round(rectF.left), Math.round(rectF.top),
                Math.round(rectF.right), Math.round(rectF.bottom));
    }

    private int clamp(int x, int min, int max) {
        if (x > max) {
            return max;
        }
        if (x < min) {
            return min;
        }
        return x;
    }

    public Camera.Size getResolution() {
        Camera.Parameters params = myCamera.getParameters();
        Camera.Size s = params.getPreviewSize();
        return s;
    }