Android中在Bitmap上画网格线

   private static Bitmap drawBackground(Bitmap bitmap,int pixInterval) {
        /**
         * 注意多个createBiamap重载函数，必须是可变位图对应的重载才能绘制
         * bitmap: 原图像
         * pixInterval: 网格线的横竖间隔，单位:像素
         */
        Bitmap copy = Bitmap.createBitmap(bitmap.getWidth(),bitmap.getHeight(), Bitmap.Config.ARGB_8888);  //很重要
        Canvas canvas = new Canvas(copy);  //创建画布
        Paint paint = new Paint();  //画笔
        paint.setStrokeWidth(1);  //设置线宽。单位为像素
        paint.setAntiAlias(true); //抗锯齿
        paint.setColor(Color.RED);  //画笔颜色
        canvas.drawBitmap(bitmap,new Matrix(),paint);  //在画布上画一个和bitmap一模一样的图
        //根据Bitmap大小，画网格线
        //画横线
        for (int i = 0; i < bitmap.getHeight() / pixInterval; i++) {
            canvas.drawLine(0, i * pixInterval, bitmap.getWidth(), i * pixInterval, paint);
        }
        //画竖线
        for (int i = 0; i < bitmap.getWidth() / pixInterval; i++) {
            canvas.drawLine(i * pixInterval, 0, i * pixInterval, bitmap.getHeight(), paint);
        }
        return copy;
    }