"CGLayer no longer recommended"; Is this the general consensus?

Question

I've written an iOS app in which I'm using CGLayer quite successfully. While researching ways to squeeze a bit more performance out of this app, I came across this blog post: http://iosptl.com/posts/cglayer-no-longer-recommended/ in which the author very broadly states that CGLayer is to never be used. An individual post alone is not cause for concern, but I've also found people referring to this post as something to abide by.

No real specifics are offered. For instance, the author states that "sometimes it's faster, sometimes it's slower". This makes me wonder if the concern is that, in general, programmers will not use this object correctly.

I suppose this question is for the seasoned Cocoa/Cocoa Touch developers. Is there any merit to this? Is CGLayer indeed something to avoid and if so, are there specific, measurable reasons as to why?

Answer 1

To start with my answer, I would like to conclude that its totally your own design decision that whether you would use CGLayer in your app or not.

The real thing is that if you are drawing something on-screen, it will possibly buy you nothing on iOS platform. On iOS, the basic screen composition block is a CALayer. CALayer takes a Quartz(CG) graphics context to draw that on screen and that might be a context created by CGLayer itself. Now, CALayer being hardware accelerated by itself, would try to cache any graphics content to graphics card and reuse them. And that's the purpose what we had used a CGLayer previously.

Also, if offscreen rendering is concerned, a CALayer can do that when shouldRasterize is set to YES and under some other circumstances. However, keep in mind that offscreen composition is again another task performed by CPU before handing over the rendered content to GPU. So again there is no clear winner.

CGLayer would be particularly handy when creating a CG context that wont be drawn on screen, like a PDF context.

I'm not sure why Apple development team has asked one to avoid CGLayer completely. Might be there are some underlying architectural flaw but that is undocumented, till date. However, until we are sure about that and we have existing apps designed over CGLayer architecture, I dont find any specific reason to completely abandon that.