Re: Reordering CALayer sublayers without raping my performance?

FROM : Chris Ryland
DATE : Mon Nov 19 19:56:42 2007

So, just to clarify for posterity, if you had turned off animation by 
using a transaction, it would have mostly or completely removed your 
slowdown?

On Nov 19, 2007, at 5:02 AM, Jonathan del Strother wrote:

> On 19 Nov 2007, at 09:49, David Duncan wrote:
>

>> On Nov 19, 2007, at 1:09 AM, Jonathan del Strother wrote:
>>

>>> Would you run that past me again?  Changing the zPosition re-sorts 
>>> the sibling layers?  In which case, is there any point in re-
>>> sorting the child array to specify render order?

>>
>> Whenever the zPosition of a layer changes, you have to sort the 
>> layers (internally) for presentation, otherwise you wouldn't get 
>> the correct visual effect. It doesn't sort the sublayers array, 
>> just the visual order that the layers are rendered in (which if all 
>> layers have the same zPosition is just the order in the sublayers 
>> array).
>>

>>> I'll test it out later, but I assume that CA is using a depth 
>>> buffer to make sure that higher zPositioned objects appear in 
>>> front of others, in which case the only time you need to worry 
>>> about the order of the child array ought to be if you're dealing 
>>> with transparent elements.

>>
>> CA has no guarantees of having or not having transparent content. 
>> In fact, the most common use for it (Appkit's layer based views) 
>> involves considerable amounts of transparency (mostly for 
>> antialiasing, but since the entire drawing model is supported 
>> arbitrary transparency has to be supported as well).
>>

>>> Is there any way of re-sorting the child element array that 
>>> doesn't incur a huge performance & memory hit?

>>
>>
>> The alternative is what I said last time, to use the current 
>> transaction to disable creating implicit animations.

>
> Oooh, it's finally clicked that re-sorting the sublayers is an 
> animated process.  That would explain the memory usage pattern I was 
> seeing, since I would have been created a lot of overlapping 
> animations...
>
> Thanks for clarifying that
>
> Jon
>
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Cheers!
--Chris Ryland / Em Software, Inc. / www.emsoftware.com