c - 在灰度像素图像中绘制矩形

Question

我正在拍摄黑色像素的图像并使用此函数绘制白色矩形。该函数的维度取正值和负值，负值向上和向左移动，正值向下和向右移动。它需要正值，我尽力在代码中考虑负值，但是当矩形的高度为负值时，它会被完全绘制错误。我们还可以假设输入永远不会超出图像的范围。为什么负宽度显示不正确？我有其他程序可以在屏幕上绘制它。 输入示例: 绘制矩形( img, 20, 20, 10, 10 , 8, -8, 255 ); img 是像素数组 (uint8_t)

void draw_rectangle( uint8_t array[], unsigned int cols, unsigned int rows, int x,
int y, int rect_width, int rect_height, uint8_t color ){

    unsigned int start = x + (y * cols);
    unsigned int startDown;
    unsigned int startOther;


    if(rect_height > 0){
        startDown = (x + ((y-1) * cols)) + (cols * rect_height);
    } else if(rect_height < 0){
        startDown = (x + ((y-1) * cols)) - (cols * rect_height * -1);
    }

    if(rect_width > 0){
        startOther = ((x + (y * cols)) + rect_width -1);
    } else if(rect_width < 0){
        startOther = ((x + (y * cols)) - rect_width -1) ;
    }




    if(rect_width > 0 ){ //if the width is posivite

        unsigned int drawIndex = 0; 
        while(drawIndex < rect_width){
            //if((x + rect_width) < cols){
                array[start + drawIndex] = color;
                array[startDown + drawIndex] = color; 
            //}
            drawIndex++;
        } 

    } else if(rect_width < 0){ //if the width is negative

        unsigned int posValue = rect_width * -1;
                    while(posValue > 0){
            //if((x - rect_width) >= 0){
                array[start - posValue + 1] = color;
                array[startDown - posValue + 1] = color; 
            //}
            posValue--;
        }
    }

    if(rect_height > 0){
        unsigned int drawIndex = 0;
        while(drawIndex < rect_height){
            //if((x + rect_width) < cols){
                array[start + (drawIndex * cols)] = color;
                array[startOther + (drawIndex * cols)] = color; 
            //}
            drawIndex++;
        } 

    } else if(rect_height < 0){ //if the height is negative

        unsigned int posValue = rect_height * -1;
                while(posValue > 0){
            //if((x - rect_width) >= 0){
                    array[start - (posValue * cols)] = color;
                    array[start - (posValue * cols)] = color; 
            //}
            posValue--;
                    }


    }

}

Answer 1

我认为您可能忘记更改此处的“else if”代码块:

里面不应该有“startOther”吗，就像宽度 block 一样？

if(rect_height > 0){
    unsigned int drawIndex = 0;
    while(drawIndex < rect_height){
        //if((x + rect_width) < cols){
            array[start + (drawIndex * cols)] = color;
            array[startOther + (drawIndex * cols)] = color; 
        //}
        drawIndex++;
    } 

} else if(rect_height < 0){ //if the height is negative

    unsigned int posValue = rect_height * -1;
            while(posValue > 0){
        //if((x - rect_width) >= 0){
                array[start - (posValue * cols)] = color;
                array[start - (posValue * cols)] = color; 
        //}
        posValue--;
                }


}

即 尝试改变这个:

array[start - (posValue * cols)] = color;
array[start - (posValue * cols)] = color;

对此:

array[start - (posValue * cols)] = color;
array[startOther - (posValue * cols)] = color;