[英]EXC_BAD_ACCESS while Flood Filling in Objective C
我在iPad应用程序中当前使用的目标c中编写了一个递归泛洪填充方法。
我通过图像的RGBA原始数据获得用户在UIImage中触摸的点的颜色。
问题是它运行了一段时间,然后在访问原始数据时应用程序崩溃并显示EXC_BAD_ACCESS。 我的问题是为什么这是“堆栈溢出”? 并且任何人都可以提出解决此问题的方法/对此方法进行改进。
这是我的方法(很抱歉,这可能会更干净)。
-(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
递归方法是导致堆栈溢出异常的主要原因,因为每个递归调用都被推入堆栈直到达到结束条件,尤其是在洪水填充算法中,这种方法根本不适用,与现代计算机相比,ipad的资源有限,请考虑使用基于循环的方法填充算法或扫描线算法的实现
有关更多信息,请访问此链接洪水填充算法
您必须检查是否没有超出为图像分配的内存。 您正在检查currentPoint.x>=0 && currentPoint.y>=0
。 但这并不能阻止您在最后一行上通过图像的末尾。
您需要检查currentPoint.y < height && currentPoint.x < width
。
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