iOS设置截图背景图片透明

/**
设置图片背景为透明
*/
- (UIImage *)imageToTransparent {
// 分配内存
const int imageWidth = self.size.width;
const int imageHeight = self.size.height;
size_t bytesPerRow = imageWidth * 4;
uint32_t *rgbImageBuf = (uint32_t *)malloc(bytesPerRow * imageHeight);

// 创建conxt
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(rgbImageBuf, imageWidth, imageHeight, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast);
CGContextDrawImage(context, CGRectMake(0, 0, imageWidth, imageHeight), self.CGImage);

// 遍历像素
int pixelNum = imageWidth * imageHeight;
uint32_t *pCurPtr = rgbImageBuf;
for (int i = 0; i < pixelNum; i++, pCurPtr++) {
if ((*pCurPtr & 0xFFFFFF00) == 0xffffff00) {
uint8_t *ptr = (uint8_t *)pCurPtr;
ptr[0] = 0;
}
}

// 将内存转成image
CGDataProviderRef dataProvider = CGDataProviderCreateWithData(NULL, rgbImageBuf, bytesPerRow * imageHeight, ProviderReleaseData);
CGImageRef imageRef = CGImageCreate(imageWidth, imageHeight, 8, 32, bytesPerRow, colorSpace, kCGImageAlphaLast | kCGBitmapByteOrder32Little, dataProvider, NULL, true, kCGRenderingIntentDefault);
CGDataProviderRelease(dataProvider);

UIImage *resultImage = [UIImage imageWithCGImage:imageRef];

// 释放
CGImageRelease(imageRef);
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);

return resultImage;
}