Re: Opal, CGLayer and OpenGL in UIKit

[Eric Wasylishen]

On 2011-09-30, at 11:00 AM, David Chisnall wrote:

> On 30 Sep 2011, at 17:48, Ivan Vučica wrote:
> 
>> Hi,
>> 
>> I've been reading the Apple docs on Quartz/CoreGraphics, and I've stumbled 
>> upon CGLayer. Upon first look, it looks like CGLayer is already implemented.
>> 
>> My first thought is that perhaps we don't need to actually use OpenGL when 
>> implementing UIKit, at least not initially. What do you guys think?
> 
> CGLayer is implemented, but it currently only does the very basic stuff.  It 
> currently uses a Cairo pattern to allow it to be composited.  This works, but 
> it's going to be fairly slow.

Right - but there's no need for my CGLayer implementation be slower than Quartz 
- it's all up to cairo. It's worth looking into the cairo gl backend (not 
released yet, afaik) - I've never tried it. I believe cairo is designed in such 
a way so that cairo backends can easily provide fast paths for things like 
drawing a source surface onto a destination.

>  UIKit (and modern AppKit) do a lot more.  For example, even the very basic 
> swoosh effect as you slide a layer off the screen is going to require 
> compositing the texture a few dozen times.  This can be very fast in OpenGL, 
> but is likely to be slow with Cairo.  CoreAnimation wants to move layers 
> around in 3D space (well, rotate them in 3D, move them in 2D), while 
> CoreImage wants to run shader programs on them.  All of these things are 
> trivial with OpenGL, but very hard in Cairo.
> 
> So, in theory it's possible, but in practice it will be hard.
> 

On another topic, Ivan, did you look in to http://chameleonproject.org/? I 
remember it was discussed before here. Personally, I think it would be cooler 
to further develop gnustep-gui and integrate opal (and maybe write a core 
animation implementation) such that chameleon can run on GNUstep, rather than 
write another uikit implementation. 

Cheers
Eric