Care to post a video on a Google drive so that we can see it?
One of my tricks (not just mine) is to have a 3 slots of for images, not just
2. When a new image loads, take the foreground one that is blended in to 100%,
put an identical one ahead of it. Make the changes to the new and old images
behind it, then hide that foreground image.
You’re actually using a copy of the foreground image as a mask and you perform
the swap behind it, then update the screen, then remove the top level one and
refresh again.
This is if I’m understanding what you’re going properly.
I’d expect that Apple’s video system to actually handle this if it still triple
buffers, but it’s been 25 years since I read the docs on the Mac’s video
subsystem.
In the mean time, add logging code that you can put breatpoints on and take a
screen grab when you log. That should help.
Cheers,
Alex Zavatone
> On May 12, 2020, at 3:27 PM, Gabriel Zachmann via Cocoa-dev
> <cocoa-dev@lists.apple.com> wrote:
>
> Thanks a million to everyone who has shared insights, hints, and advice on
> this.
>
> I have restructured my code, so now I do the heavy lifting of loading images
> in a serial dispatch queue.
> However, there is still sometimes some stuttering visible in the animation of
> the images.
> Does anyone have an idea what might be causing it?
>
> Here is the current structure of my code, given in sort of a pseudo-code:
>
> -animateOneframe:
> // essentially, this gets called when the next image is to be displayed
> current_image_ = prefetched_image_; // these are CGImageRef's
> dispatch_async( prefetch_queue_, ^{
> [self loadNextImage];
> } );
> create a new CALayer,
> assign the current_image_ as content,
> create an animation for the layer,
> add the layer to the layer hierarchy
>
> In -loadNextImage, I am doing all the heavy lifting of loading images
> (and the not-so-heavy), such as:
> prefetched_image_ = nil;
> CGImageSourceGetStatus
> CGImageSourceCopyPropertiesAtIndex
> CGImageSourceCreateThumbnailAtIndex
> imageByApplyingOrientation
> createCGImage
> prefetched_image_ = new image
>
> (I know there is some potential race condition here, but that is not of
> concern to me right now.)
>
> Overall, I get the impression that it is "better" (less stuttering),
> but sometimes there is still a stuttering in the animation when the app
> makes a transition from one image to the next one.
>
> How could that be?
>
> Using Instruments, I can see this in the "heaviest stack trace" when CPU
> usage is high in the main thread:
>
> 41 CoreFoundation 3897.0 __CFRunLoopDoObservers
> 40 CoreFoundation 3897.0
> __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__
> 39 QuartzCore 3896.0
> CA::Transaction::observer_callback(__CFRunLoopObserver*, unsigned long, void*)
> 38 QuartzCore 3896.0 CA::Transaction::commit()
> 37 QuartzCore 3895.0 CA::Context::commit_transaction(CA::Transaction*,
> double)
> 36 QuartzCore 3895.0 CA::Layer::prepare_commit(CA::Transaction*)
> 35 QuartzCore 3895.0 CA::Render::prepare_image(CGImage*, CGColorSpace*,
> unsigned int, double)
> 34 QuartzCore 3895.0 CA::Render::copy_image(CGImage*, CGColorSpace*,
> unsigned int, double, double)
> 33 QuartzCore 3895.0 CA::Render::(anonymous
> namespace)::create_image_by_rendering(CGImage*, CGColorSpace*, unsigned int,
> double, CA::Render::ImageCopyType)
>
> Are these functions the culprits? How can I make them get executed in the
> background?
>
>
> All insights will be highly appreciated.
>
> Best regards, Gabriel
>
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