在目標C中填充洪水時為EXC_BAD_ACCESS

Question

我在iPad應用程序中當前使用的目標c中編寫了一個遞歸泛洪填充方法。

我通過圖像的RGBA原始數據獲得用戶在UIImage中觸摸的點的顏色。

問題是它運行了一段時間，然后在訪問原始數據時應用程序崩潰並顯示EXC_BAD_ACCESS。 我的問題是為什么這是“堆棧溢出”？ 並且任何人都可以提出解決此問題的方法/對此方法進行改進。

這是我的方法（很抱歉，這可能會更干凈）。

-(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;
    }

謝謝-TJ

Answer 1

遞歸方法是導致堆棧溢出異常的主要原因，因為每個遞歸調用都被推入堆棧直到達到結束條件，尤其是在洪水填充算法中，這種方法根本不適用，與現代計算機相比，ipad的資源有限，請考慮使用基於循環的方法填充算法或掃描線算法的實現

有關更多信息，請訪問此鏈接洪水填充算法

Answer 2

您必須檢查是否沒有超出為圖像分配的內存。 您正在檢查currentPoint.x>=0 && currentPoint.y>=0 。 但這並不能阻止您在最后一行上通過圖像的末尾。

您需要檢查currentPoint.y < height && currentPoint.x < width 。