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我在目标 c 中编写了一个递归洪水填充方法，我目前在 iPad 应用程序中使用该方法。

我通过图像的 RGBA 原始数据获取用户在 UIImage 中触摸的点的颜色。

问题是它运行了一段时间，然后应用程序在访问原始数据时崩溃并出现 EXC_BAD_ACCESS。我的问题是为什么，这是“堆栈溢出”吗？并且任何人都可以提出解决此问题/改进此方法的方法。

这是我的方法（它可能更干净，我很抱歉）。

-(unsigned char *)floodFill:(unsigned char *)data withImageRef:(CGImageRef)imgRef withColor:(UIColor *)color whereColor:(UIColor *)pixelColor atX:(int)xx andY:(int)yy
    {
        //create points for top bottom left and right pixel
        CGPoint top = CGPointMake(xx, yy-1);
        CGPoint bottom = CGPointMake(xx, yy+1);
        CGPoint left = CGPointMake(xx-1, yy);
        CGPoint right = CGPointMake(xx+1, yy);

        //convert new color to rgba values
        const CGFloat *rgb = CGColorGetComponents(color.CGColor);

        float newRed = rgb[0];
        float newGreen = rgb[1];
        float newBlue = rgb[2];
        float newAlpha = CGColorGetAlpha(color.CGColor);

        //convert old color to rgba values
        const CGFloat *rgb2 = CGColorGetComponents(pixelColor.CGColor);

        float oldRed = rgb2[0];
        float oldGreen = rgb2[1];
        float oldBlue = rgb2[2];
        float oldAlpha = CGColorGetAlpha(pixelColor.CGColor);

        NSUInteger width = CGImageGetWidth(imgRef);
        NSUInteger bytesPerPixel = 4;
        NSUInteger bytesPerRow = bytesPerPixel * width;
        int byteIndex = (bytesPerRow * yy) + xx * bytesPerPixel;

        //color current pixel
        data[byteIndex] = (char)newRed*255;
        data[byteIndex+1] = (char)newGreen*255;
        data[byteIndex+2] = (char)newBlue*255;
        data[byteIndex+3] = (char)newAlpha*255;


        CGFloat red, green, blue, alpha;
        CGPoint currentPoint;

        //check top pixel
        currentPoint=top;
        if(currentPoint.x>=0 && currentPoint.y>=0)
        {
            byteIndex = (bytesPerRow * currentPoint.y) + currentPoint.x * bytesPerPixel;
            red   = (data[byteIndex]     * 1.0) / 255.0;
            green = (data[byteIndex + 1] * 1.0) / 255.0;
            blue  = (data[byteIndex + 2] * 1.0) / 255.0;
            alpha = (data[byteIndex + 3] * 1.0) / 255.0;
            if(red==oldRed&&green==oldGreen&&blue==oldBlue&&alpha==oldAlpha)
                data=[self floodFill:data withImageRef:imgRef withColor:color whereColor:pixelColor atX:currentPoint.x andY:currentPoint.y];
        }

        //check bottom pixel
        currentPoint=bottom;
        if(currentPoint.x>=0 && currentPoint.y>=0)
        {
            byteIndex = (bytesPerRow * currentPoint.y) + currentPoint.x * bytesPerPixel;
            red   = (data[byteIndex]     * 1.0) / 255.0;
            green = (data[byteIndex + 1] * 1.0) / 255.0;
            blue  = (data[byteIndex + 2] * 1.0) / 255.0;
            alpha = (data[byteIndex + 3] * 1.0) / 255.0;
            if(red==oldRed&&green==oldGreen&&blue==oldBlue&&alpha==oldAlpha)
                data=[self floodFill:data withImageRef:imgRef withColor:color whereColor:pixelColor atX:currentPoint.x andY:currentPoint.y];
        }

        //check left pixel
        currentPoint=left;
        if(currentPoint.x>=0 && currentPoint.y>=0)
        {
            byteIndex = (bytesPerRow * currentPoint.y) + currentPoint.x * bytesPerPixel;
            red   = (data[byteIndex]     * 1.0) / 255.0;
            green = (data[byteIndex + 1] * 1.0) / 255.0;
            blue  = (data[byteIndex + 2] * 1.0) / 255.0;
            alpha = (data[byteIndex + 3] * 1.0) / 255.0;
            if(red==oldRed&&green==oldGreen&&blue==oldBlue&&alpha==oldAlpha)
                data=[self floodFill:data withImageRef:imgRef withColor:color whereColor:pixelColor atX:currentPoint.x andY:currentPoint.y];
        }

        //check right pixel
        currentPoint=right;
        if(currentPoint.x>=0 && currentPoint.y>=0)
        {
            byteIndex = (bytesPerRow * currentPoint.y) + currentPoint.x * bytesPerPixel;
            red   = (data[byteIndex]     * 1.0) / 255.0;
            green = (data[byteIndex + 1] * 1.0) / 255.0;
            blue  = (data[byteIndex + 2] * 1.0) / 255.0;
            alpha = (data[byteIndex + 3] * 1.0) / 255.0;
            if(red==oldRed&&green==oldGreen&&blue==oldBlue&&alpha==oldAlpha)
                data=[self floodFill:data withImageRef:imgRef withColor:color whereColor:pixelColor atX:currentPoint.x andY:currentPoint.y];
        }



        return data;
    }

谢谢-TJ

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2 回答 2

0

递归方法是堆栈溢出异常的主要原因，因为每个递归调用都被压入堆栈直到达到结束条件，特别是在洪水填充算法中这种方法根本不适合，与现代计算机相比，ipad 资源有限，考虑使用基于循环洪水填充算法或扫描线算法的实现

欲了解更多信息，请访问此链接洪水填充算法

于 2012-11-28T04:12:32.727 回答
-1

您必须检查您没有超出为图像分配的内存。您在检查currentPoint.x>=0 && currentPoint.y>=0. 但这并不能阻止您在最后一行时通过图像的末尾。

你需要做检查currentPoint.y < height && currentPoint.x < width。

于 2012-11-28T04:12:15.377 回答