Re: GDK-DirectFB Patches

[Denis Oliver Kropp <dok directfb org>]

Carl Worth wrote:
> On Thu, 06 Dec 2007 09:44:55 +0100, Denis Oliver Kropp wrote:
>> Carl Worth wrote:
>>> For interleaving cairo and non-cairo rendering, cairo provides the
>>> cairo_surface_flush and cairo_surface_mark_dirty APIs. Does
>>> cairo-directfb implement those and does your application use them.
>> Thanks for the pointer. The cairo-directfb backend seems to do nothing
>> in these functions. I'm not sure what it's supposed to do. Should the
>> first accumulate a region to flip and the second actually flips?
> 
> I don't know how cairo-directfb surface is implemented exactly. So
> I'll describe the general concepts and then illustrate them by way of
> a fictitious "shadow" backend that is implemented with a
> cairo-image-surface internally and can copy back and forth between
> that and some underlying "system" object.
> 
> When an application wants to switch from cairo- to non-cairo-based
> drawing it should call cairo_surface_flush. In this case, our shadow
> backend would copy its state from the image surface to the underlying
> system. (Ideally it would copy a minimal region based on the extents
> of cairo drawing operations that have occurred, but cairo's current
> backend interfaces don't make it easy to know this. But there would be
> no API impact from improving that.)
> 
> Then, when an application wants to switch back from non-cairo- to
> cairo-based drawing it should call cairo_surface_mark_dirty_rectangle
> one or more times. Our shadow backend would accumulate a region from
> these rectangles and before the next cairo drawing operation would
> copy that region from the system to the image surface.
> 
> Does that make sense?

Yes. Thanks for your explanation.

The cairo-directfb surface uses the "system" object directly, which is an
IDirectFBSurface. For each source/dest acquire it does a Lock() to get the
surface data pointer and pitch and calls cairo_image_surface_create_for_data()
which is not too heavy for every acquire I hope.

So flushing and marking is not required.

-- 
Best regards,
  Denis Oliver Kropp

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