Question

我在目标c中编写了一个递归填充方法，我目前正在iPad应用中使用。

我通过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了EXC_BAD_ACCESS。我的问题是为什么，这是一个“堆栈溢出”？任何人都可以建议一种方法来解决这个问题/改进这种方法。

这是我的方法（它可能更干净，我道歉）。

-(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

Answer 1

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推送到堆栈直到达到最终条件，特别是在泛洪填充算法中这种方法根本不适合，ipad与现代计算机相比资源有限，考虑使用基于循环的洪水填充算法或扫描线算法实现

有关详细信息，请访问此链接Flood Fill algorithms

Answer 2

您必须检查不要超出为图像分配的内存。您在currentPoint.x>=0 && currentPoint.y>=0的支票中部分执行此操作。但是当你在最后一排时，这并不会阻止你通过图像的末尾。

您需要检查currentPoint.y < height && currentPoint.x < width。

目标C中的洪水填充时的EXC_BAD_ACCESS

2 个答案: