[cairo] why cairo is so slow on Windows, is there any plan to improve cairo performance on Windows?

[Vladimir Vukicevic]

Right, that's going to be slow.  What Owen is suggesting is that you 
create an image surface the same size as your update region, then draw 
your rotated image into it.  Then use StretchDIBits or equivalent to 
draw it onto the window's DC.

Or, create a win32 DIB surface using cairo_win32_surface_create_with_dib 
as your destination, and then draw that onto the window DC, since that 
operation will be fast.  If I'm not making sense:

HDC winDC;
cairo_surface_t *winSurf = cairo_win32_surface_create_for_dc(winDC);
cairo_surface_t *target = cairo_win32_surface_create_with_dib(..., 
width, height);
cairo_surface_t *src = cairo_image_surface_create(...);

draw src -> target rotated, etc.
finally draw target -> winSurf 1:1, no rotation, etc.

     - Vlad

On 6/29/09 7:20 PM, Rainman Lee wrote:
> I did not use DDB bitmap :@)
> I just created a image surface from a png file and a cairo win32
> surface from a window dc,
> then fill the win32 surface with the image surface by rotation
> transforms from 0 degree up to 360 degree.
>
> On Tue, Jun 30, 2009 at 4:01 AM, Owen Taylor<otaylor at redhat.com>  wrote:
>> On Mon, 2009-06-29 at 12:48 +0800, Rainman Lee wrote:
>>> Hi everyone,
>>> I use cairo on windows for a while. I found that cairo was so slow
>>> whenever fill a surface to another with scaling, rotating, or even a
>>> non-integer translaton. I compared it with GDI+, which is at least 7
>>> times faster than cairo :(
>>>
>>> It seems that if a source pixel can not map to a dest pixel which has
>>> an integer coordinate, cairo will use a subpixel algorithm, and it
>>> will terribly hurt the performance. I made a filling test, firstly by
>>> a 0.5 pixel step horz translation transform, and a 1 pixel step horz
>>> translation transform then, each of which looped 100 times. the first
>>> case was extremely slow than the second one.
>>>
>>> Is there any idea to speed up cairo in this case? I tryed to set
>>> antialias with none, but it had no effect.
>>
>> Only a very small subset of Cairo can be done using hardware
>> acceleration via the GDI API. For everything else, if your bitmap
>> is in video memory (a DDB) Cairo will need to read, make the changes
>> and write back. This is very slow.
>>
>> For complex rendering, you are much better off rendering to a DIB.
>>
>> - Owen
>>
>>
>>
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