I've just started with releasing in core graphics, so I might need a little help.
I have code which looks like this:
UIImage *buttonImage() {
UIGraphicsBeginImageContextWithOptions(bounds.size, NO, 0);
CGContextRef context = UIGraphicsGetCurrentContext();
CGColorSpaceRef baseSpace = CGColorSpaceCreateDeviceRGB();
CGMutablePathRef outerPath;
CGMutablePathRef midPath;
CGMutablePathRef innerPath;
CGMutablePathRef highlightPath;
//Some button stuff
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
CGContextRelease(context);
return image;
}
That release line, I've put in. I'm getting an error with it though:
context_reclaim: invalid context
context_finalize: invalid context
Any thoughts as to where i should put the release in this instance?
You only need to do CGContextRelease(context) if you have previously done a CFRetain(context) or a CGContextRetain(context), or if you created the context yourself. In your example, you are calling UIGraphicsBeginImageContextWithOptions(), which is handling the creation of the context for you, thus, calling CGContextRelease() yourself is over-releasing it.
You do need to balance the CGColorSpaceCreateDeviceRGB() with either a:
CGColorSpaceRelease(baseSpace)
or a :
if (baseSpace) CFRelease(baseSpace)
You don't own the context when using UIGraphicsGetCurrentContext. Therefore you should not be releasing it. If you were to use CGContextRetain() then you would release. More information of this is available here:
Memory Management Guide for Core Foundation
I highly suggest reading the Memory Management programming guide to get an understanding of how it works.
Related
I am working with drawing project, as we know to draw something we need to get call this function, UIGraphicsGetCurrentcontext, So I am also calling it wherever, I need it, either its clear, or erase . What I am doing is in every function, I am calling it this way
CGContextRef context = UIGraphicsGetCurentContext()
What I want to know, is whether I get the same context whenever I call this function? whether the pointer points to same context?
Because my eraser works in some cases and fails in some cases.
Below is my eraser function
- (void)erase
{
[m_curImage drawAtPoint:CGPointMake(0, 0)];
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextClearRect(context, rect);
}
Regards
Ranjit
You can only use UIGraphicsGetCurentContext() inside of the drawRect method, outside of that it will not be configured with a valid context.
You have to create a custom view and write your erase() method code in the drawRect method.
I currently working on encapsulation many [NSString drawAtPoint:withFont:] function calls to a method so that I could draw lots of strings by a single call, but how can I tell the method where to draw these strings?
What if I pass a CGContextRef to it, how to set a CGContextRef as current context?
On iOS 4 and later, wrap the NSString drawAtPoint calls with UIGraphicsPushContext(context) and UIGraphicsPopContext().
See accepted answer for "Using NSStrings drawAtPoint method in place of CGContextShowGlyphsAtPoint..."
Maybe you need this part of code:
CGContextRef context = UIGraphicsGetCurrentContext();
I'm using CGDataProviderCreateWithData to (eventually) create a UIImage from a malloced array of bytes. I call CGDataProviderCreateWithData like this:
provider = CGDataProviderCreateWithData(NULL, dataPtr, dataLen, callbackFunc);
where
dataPtr is the previously malloced array of data bytes for the image,
dataLen is the number of bytes in the dataPtr array, and
callbackFunc is as described in the CGDataProviderCreateWithData documentation:
void callbackFunc(void *info, const void *data, size_t size);
The callback function is called when the data provider is released so I could free() dataPtr there, but I may want to continue using it (dataPtr) and at some later stage free it. This block of code will be called multiple times, and the flow will look something like:
malloc(dataPtr)
create image (call CGDataProviderCreateWithData etc)
display image
release image (and so release data provider created by CGDataProviderCreateWithData)
continue to use dataPtr
free(dataPtr)
so 1..6 may be executed multiple times. I don't want dataPtr hanging around for the entire execution of the program (and it may change in size anyway), so I want to malloc/free it as necessary.
The problem is that I can't free(dataPtr) in the callback from CGDataProviderCreateWithData because I still want to use it, so I want to free it some time later - and I can't free it until I know that the data provider no longer needs it (as far as I can tell CGDataProviderCreateWithData uses the array I pass, it doesn't take a copy).
I can't do (1) above until I know it is ok to free and re-malloc dataPtr, so what I really want to do is block waiting for the data provider to be freed (well, I want to know whether I should re-enter the 1..6 block of code, which I can't do until the data provider is freed). It will be - I create the data provider, create the image and immediately display it and release the data provider. The trouble is that the data provider isn't actually released until the UIImage is released and is finished with it.
I'm reasonably new to objective-c and iOS. Am I missing something obvious?
If you malloc the memory for the provider's data, you really want to to free it in the callback. Do not be tempted to try to circumvent this in any manner. It be too easy to leak and would be susceptible to simple memory issues.
Having said that, there are two simple solutions that address your question. Either:
Make your own copy of the data that you'll manage separately from the provider; or
Instead of using the void * renditions of the CGDataProvider methods, use the CFData rendition (e.g. CGDataProviderCreateWithCFData) and then you can maintain your own strong reference to this data object (or if in non-ARC code, do your own retain of the data object). The object will not be deallocated until all strong references are resolved (or, in non-ARC code, all of your manual retain calls are resolved with a corresponding release or autorelease call).
With either of these approaches, you can continue to let CGProviderRef manage the memory as it sees fit, but you can continue to use the data object for your own purposes, too.
I ran into a similar problem as well. I wanted to use CGImageCreateWithJPEGDataProvider, so used CGDataProviderRef with a malloc'd byte array. I was getting the same problem, when trying to free the byte array at some point after creating the Data Provider Reference.
It occurs because the data provider reference takes over the ownership of the byte array, so can only be freed by the reference, when it is done with it.
I agree with #TheBlack in that if you need the data elsewhere, make a copy of it.
What I'm doing is essentially the same to what you want to achieve, I just took different route.
This whole process is wrapped into NSOperation so you have control over scheduling memory usage.
CGImageRef imageRef = [image CGImage];
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
CGColorSpaceRef colorSpace = CGImageGetColorSpace(imageRef);
NSUInteger bitsPerComponent = CGImageGetBitsPerComponent(imageRef);
UInt8 *rawData = calloc((height * width * bitsPerComponent), sizeof(UInt8));
NSUInteger bytesPerRow = CGImageGetBytesPerRow(imageRef);
CGContextRef context = CGBitmapContextCreate(rawData, width, height,
bitsPerComponent, bytesPerRow, colorSpace,
kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Host);
if (context)
{
CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
// This is the place you get access to data trough rawData. Do whatever you want with it, when done, get image with
CGImageRef newImg = CGBitmapContextCreateImage(context);
}
OR
subclass CALayer, override drawInContext and use CGBitmapContextGetData to get raw data. Don't have much experience with this though, sorry, but if you want to see instant changes
on image based on user input, I'd do it this way:
Subclass UIView and CALayer which becomes layer for view and displays image. View gets input and image data (from CGBitmapContextGetData) in layer class is manipulated based on input.
Even CATiledLayer can be used for huge images in this way. When done with image, just release UIView and replace it with new one. I'll gladly provide help if you need any, just ping here.
I'm trying to load an image from a url inside of drawRect:. Our image-loading code is a method that looks like this: - (void) loadImage:(NSURL*)url done:(void(^)(UIImage*))done;, which creates an asynchronous NSURLConnection and calls back with the image.
So, my code in drawRect: looks like this:
CGContextRef context = UIGraphicsGetCurrentContext()
[service loadImage:url done:^(UIImage * image){
CGContextDrawImage(context, frame, image.CGImage);
}];
Unfortunately, this doesn't work. The image is never drawn.
I've also tried using synchronous connections ([NSData dataWithContentsOfUrl:]), but it blocks the thread and slows things down unnecessarily. I don't want to use a UIImageView.
What is the correct way to do this? Thanks!
I think the correct way would either be to load the image beforehand or draw the image as soon as you receive it by either calling "setNeedsDisplayInRect:" or doing your own drawing handling in a separate method (iOS might discourage you from doing this though, I am not sure). Obviously the setNeedsDisplayInRect variation would require you to have the image at hand for drawing the second time around (cache it).
If you load the image asynchronously your drawRect method will moste likely have exited before the image is loaded and the draw focus is no longer locked on your drawRect, thus making it impossible to draw the image in the context. Did you try to set a breakpoint to verify this though? I might be wrong about the locking, but thought I read something alike this at some point.
Think it through--why would it run? There's no guarantee that context is still the current context (or even that its backing store is still fully valid) by the time the block is entered. By using an asynchronous callback, be it a block or a delegate method or something else, you're intentionally deferring code to a later point in time. The call to -drawRect: has ended and is off the stack long before your block is entered.
The first thing I would try is to make sure the async handler runs on the main thread:
[service loadImage:url done:^(UIImage * image) {
dispatch_async(dispatch_get_main_queue(), ^{
CGContextDrawImage(context, frame, image.CGImage);
});
}];
If that does not help, I would start to wonder if the context is still valid. The pointer is, but the context probably not. Maybe you could move the context acquisition to the handler:
[service loadImage:url done:^(UIImage * image) {
dispatch_async(dispatch_get_main_queue(), ^{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextDrawImage(context, frame, image.CGImage);
…
});
}];
Not sure if that makes sense API-wise, I don’t do much stuff like this.
Have you tried:
__block CGContextRef context = UIGraphicsGetCurrentContext()
[service loadImage:url done:^(UIImage * image){
CGContextDrawImage(context, frame, image.CGImage);
}];
You may have to do the same thing with frame, so when the block returns it knows what context and frame it should modify.
When you create a CGLayer like so, and then get the context...it appears to be impossible to release the CGContextRef?
Releasing the CGLayerRef itself (apparently) works fine.
You'd think you could release the CGContextRef just before releasing the CGLayer - but no? Nor can you release the CGContextRef just after releasing the CGLayer.
If you release the CGContextRef, the app crashes.
CGLayerRef aether = CGLayerCreateWithContext(
UIGraphicsGetCurrentContext(), CGSizeMake(1024,768), NULL);
CGContextRef weird = CGLayerGetContext(aether);
// paths, strokes, filling etc
// paths, strokes, filling etc
// try releasing weird here
CGLayerRelease(aether);
// or, try releasing weird here
Does anyone know what is going on here? (Note further that CGContextRelease is indeed just the same as CFRelease, with some nil checking.)
In fact should you never manually release CGContextRef? Does anyone know? Cheers.
CGContextRelease(weird); // impossible, not necessary, doesn't work???
Regarding Joel's spectacular answer below:
Is releasing the CGLayerRef correct and proper? Joel has pointed out:
"Yes, since the function you're obtaining it from has 'Create' in its signature. See: documentation/CoreFoundation/"
You do not own the context returned from CGLayerGetContext, and so should not release it*. In particular, see http://developer.apple.com/library/mac/#documentation/CoreFoundation/Conceptual/CFMemoryMgmt/Concepts/Ownership.html#//apple_ref/doc/writerid/cfGetRule for information regarding 'Get' functions in Core Foundation.
*: at least, you shouldn't release it given your example code. If you retained it first (CGContextRetain(weird)), then you should have a CGContextRelease to balance it.