我发现一个解决方案,每次必须调整大小时创建一个新的较大的上下文。这里的神奇功能:
void MPResizeContextWithNewSize(CGContextRef *c, CGSize s) {
size_t bitsPerComponents = CGBitmapContextGetBitsPerComponent(*c);
size_t numberOfComponents = CGBitmapContextGetBitsPerPixel(*c)/bitsPerComponents;
CGContextRef newContext = CGBitmapContextCreate(NULL, s.width, s.height, bitsPerComponents, sizeof(UInt8)*s.width*numberOfComponents,
CGBitmapContextGetColorSpace(*c), CGBitmapContextGetBitmapInfo(*c));
// Copying context content
CGImageRef im = CGBitmapContextCreateImage(*c);
CGContextDrawImage(newContext, CGRectMake(0, 0, CGBitmapContextGetWidth(*c), CGBitmapContextGetHeight(*c)), im);
CGImageRelease(im);
CGContextRelease(*c);
*c = newContext;
}
我不知道是否可以优化,例如用memcpy
,as suggested here。我尝试过,但它使我的代码崩溃。