BAD_ACCESS when trying to free data when UIView to UIImage - iphone

Question

I intended to take a snapshot of a UIView that drawed by OpenGL ES into an UIImage, here is the code I used:
if(context){
[EAGLContext setCurrentContext:context];
glBindFramebuffer(GL_FRAMEBUFFER, defaultFramebuffer);
NSInteger dataLength = framebufferWidth * framebufferHeight * 4;
GLubyte* data = (GLubyte*)malloc(dataLength) ; // malloc(myDataLength);
glReadPixels(0, 0, framebufferWidth, framebufferHeight, GL_RGBA, GL_UNSIGNED_BYTE, data);
// make data provider with data.
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, data, dataLength, NULL);
// prep the ingredients
int bitsPerComponent = 8;
int bitsPerPixel = 32;
int bytesPerRow = 4 * framebufferWidth;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
// make the cgimage
CGImageRef result = CGImageCreate(framebufferWidth, framebufferHeight, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
// then make the uiimage from that
UIImage *image = [UIImage imageWithCGImage:result];
CGImageRelease(result);
CGColorSpaceRelease(colorSpaceRef);
CGDataProviderRelease(provider);
//free(data);
return image;
}
I was intended to use free(data); before return, but that would raises a BAD_ACCESS runtime error.
So my questions is, how to free properly? Or should I free them after the image releases?

Answer 1

You should use CGDataProviderCreateWithData's CGDataProviderReleaseDataCallback as described here.
Simply add the freeData function callback:
void freeData(void *info, const void *data, size_t size)
{
free((void*)data);
}
and pass it to CGDataProviderCreateWithData:
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, data, dataLength, freeData);

Answer 2

This is my current code and it works just fine.
if(context){
[EAGLContext setCurrentContext:context];
glBindFramebuffer(GL_FRAMEBUFFER, defaultFramebuffer);
NSInteger dataLength = width * height * 4;
int bitsPerComponent = 8;
int bitsPerPixel = 32;
int bytesPerRow = 4 * width;
GLubyte* data = (GLubyte*)malloc(dataLength) ;
glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, data);
// make upside down
GLubyte* swp = (GLubyte*)malloc(width * 4);
for (int h = 0; h < height / 2; h++) {
memcpy(swp, data + (height - 1 - h) * bytesPerRow, bytesPerRow);
memcpy(data + (height - 1 - h) * bytesPerRow, data + h * bytesPerRow, bytesPerRow);
memcpy(data + h * bytesPerRow, swp, bytesPerRow);
}
NSData* nsData = [NSData dataWithBytesNoCopy:data length:dataLength freeWhenDone:YES];
// make data provider with data.
CGDataProviderRef provider = CGDataProviderCreateWithCFData((CFDataRef)nsData);
// prep the ingredients
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
// make the cgimage
CGImageRef result = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
CGColorSpaceRelease(colorSpaceRef);
CGDataProviderRelease(provider);
// then make the uiimage from that
UIImage *image = [UIImage imageWithCGImage:result];
CGImageRelease(result);
return image;
}