[cairo] performance difference between image and win32 surface?

[Vladimir Vukicevic]

Danilo Gulamhussene wrote:
> Vladimir Vukicevic schrieb:
>> Could you give some examples of the kinds of operations that you're 
>> finding slower?
>>
>>     - Vlad
> [...]
> Owens advise to use cairo_push_group() on win32 surface fixed the 
> performance difference for this test completely.
> 
> The costs of cairo_push_group(), which implicitly creates a new surface 
> (as far as I understood), on what do they depend? Do they depend on the 
> size of the original surface, the current clip region, or the space used 
> by the objects, i draw inside the group?

Ah, yeah, if you're drawing straight to a window's DC, you're paying a 
lot of overhead because that window is being immediately updated. 
Drawing to an offscreen DC, which is effectively what push_group will do 
for you, is much faster.

The size of the temporary surface created by push_group is the 
intersection of the current clip region and the bounds of the original 
surface.  It's independent of the size of any drawing you do afterwards. 
  For maximum speed, I would suggest using push_group with a COLOR-only 
content (not COLOR_ALPHA), and using OPERATOR_SOURCE to update the 
resulting window.  This should result in a fast BitBlt for the final 
update to the screen.

     - Vlad