CoreGraphics: Encode RGBA data to PNG - c

Question

I am trying to use the C interface of CoreGraphics & CoreFoundation to save a buffer of 32-bit RGBA data (as a void*) to a PNG file. When I try to finialize the CGImageDestinationRef, the following error message is printed to the console:
libpng error: No IDATs written into file
As far as I can tell, the CGImageRef I'm adding to the CGImageDestinationRef is valid.
Relavent Code:
void saveImage(const char* szImage, void* data, size_t dataSize, size_t width, size_t height)
{
CFStringRef name = CFStringCreateWithCString(NULL, szImage, kCFStringEncodingASCII);
CFURLRef texture_url = CFURLCreateWithFileSystemPath(
NULL,
name,
kCFURLPOSIXPathStyle,
false);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGDataProviderRef dataProvider = CGDataProviderCreateWithData(NULL, data, dataSize, NULL);
CGImageRef image = CGImageCreate(width, height, 8, 32, 32 * width, colorSpace,
kCGImageAlphaLast | kCGBitmapByteOrderDefault, dataProvider,
NULL, FALSE, kCGRenderingIntentDefault);
// From Image I/O Programming Guide, "Working with Image Destinations"
float compression = 1.0; // Lossless compression if available.
int orientation = 4; // Origin is at bottom, left.
CFStringRef myKeys[3];
CFTypeRef myValues[3];
CFDictionaryRef myOptions = NULL;
myKeys[0] = kCGImagePropertyOrientation;
myValues[0] = CFNumberCreate(NULL, kCFNumberIntType, &orientation);
myKeys[1] = kCGImagePropertyHasAlpha;
myValues[1] = kCFBooleanTrue;
myKeys[2] = kCGImageDestinationLossyCompressionQuality;
myValues[2] = CFNumberCreate(NULL, kCFNumberFloatType, &compression);
myOptions = CFDictionaryCreate( NULL, (const void **)myKeys, (const void **)myValues, 3,
&kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
CFStringRef type = CFStringCreateWithCString(NULL, "public.png", kCFStringEncodingASCII);
CGImageDestinationRef dest = CGImageDestinationCreateWithURL(texture_url, type, 1, myOptions);
CGImageDestinationAddImage(dest, image, NULL);
if (!CGImageDestinationFinalize(dest))
{
// ERROR!
}
CFRelease(image);
CFRelease(colorSpace);
CFRelease(dataProvider);
CFRelease(dest);
CFRelease(texture_url);
}
This post is similar, except I'm not using the Objective C interface: Saving a 32 bit RGBA buffer into a .png file (Cocoa OSX)

Answer 1

Answering my own questions:
In addition to the issues pointed out by NSGod, the IDAT issue was an invalid parameter to CGImageCreate(): parameter 5 is bytesPerRow, not bitsPerRow. So 32 * width was incorrect; 4 * width is correct.
Despite what this page of the official documentation lists, UTCoreTypes.h is located in the CoreServices.framework for MacOSX, not MobileCoreServices.framework.

Answer 2

There are numerous issues with your code.
Here it is rewritten how I would do it:
void saveImage(const char* szImage, void* data, size_t dataSize, size_t width, size_t height)
{
CFStringRef name = CFStringCreateWithCString(NULL, szImage, kCFStringEncodingUTF8);
CFURLRef texture_url = CFURLCreateWithFileSystemPath(
NULL,
name,
kCFURLPOSIXPathStyle,
false);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGDataProviderRef dataProvider = CGDataProviderCreateWithData(NULL, data,
dataSize, NULL);
CGImageRef image = CGImageCreate(width, height, 8, 32, 32 * width, colorSpace,
kCGImageAlphaLast | kCGBitmapByteOrderDefault,
dataProvider, NULL, FALSE, kCGRenderingIntentDefault);
// From Image I/O Programming Guide, "Working with Image Destinations"
float compression = 1.0; // Lossless compression if available.
int orientation = 4; // Origin is at bottom, left.
CFStringRef myKeys[3];
CFTypeRef myValues[3];
CFDictionaryRef myOptions = NULL;
myKeys[0] = kCGImagePropertyOrientation;
myValues[0] = CFNumberCreate(NULL, kCFNumberIntType, &orientation);
myKeys[1] = kCGImagePropertyHasAlpha;
myValues[1] = kCFBooleanTrue;
myKeys[2] = kCGImageDestinationLossyCompressionQuality;
myValues[2] = CFNumberCreate(NULL, kCFNumberFloatType, &compression);
myOptions = CFDictionaryCreate(NULL, (const void **)myKeys,
(const void **)myValues, 3, &kCFTypeDictionaryKeyCallBacks,
&kCFTypeDictionaryValueCallBacks);
CGImageDestinationRef dest =
CGImageDestinationCreateWithURL(texture_url, kUTTypePNG, 1, NULL);
CGImageDestinationAddImage(dest, image, NULL);
CGImageDestinationSetProperties(dest, myOptions);
if (!CGImageDestinationFinalize(dest))
{
// ERROR!
}
}
First, never use ASCII when dealing with file system paths, use UTF8. Second, you were constructing a dictionary to be used to set the properties of the image, but you were using it with the wrong function. The documentation for CGImageDestinationCreateWithURL() says the following:
CGImageDestinationCreateWithURL
Creates an image destination that writes to a location specified by a
URL.
CGImageDestinationRef CGImageDestinationCreateWithURL (
CFURLRef url,
CFStringRef type,
size_t count,
CFDictionaryRef options
);
Parameters
options - Reserved for future use. Pass NULL.
You were trying to pass a dictionary of properties when you were supposed to pass NULL. (Also, you can simply use the kUTTypePNG Uniform Type Identifier string constant instead of re-creating it). First call CGImageDestinationCreateWithURL(), then call CGImageDestinationAddImage() to add the image, then call CGImageDestinationSetProperties() and pass in the dictionary of properties you created.
[UPDATE]: If after these changes you're still having libpng error: No IDATs written into file issues, try the following: First, make sure that dataProvider is non-NULL-- in other words, make sure the CGDataProviderCreateWithData() function succeeded. Second, if dataProvider is valid, perhaps try changing the options from kCGImageAlphaLast | kCGBitmapByteOrderDefault to simply kCGImageAlphaPremultipliedLast and see if it succeeds.