[cairo] GTK+, Cairo, XLib integration for fast 2D graphics drawing

[Christos Sotiriou]

Chris, thanks for you reply. I clearly understand now the distinction
between images and X Drawables.

So, to summarise, could you please confirm that my following GTK/Cairo
interface functions correctly and always use the XServer:

1. In my expose_event function I do:

maincanvas_drawable = GTK_LAYOUT(maincanvas)->bin_window; // drawable
layout window //
maincanvas_cs = gdk_cairo_create(maincanvas_drawable); // corresponding
cairo state//

to get the Cairo State maincanvas_cs

2. Next, I draw to maincanvas_cs:

...
cairo_paint(maincanvas_cs);
...

or

3.  I create a similar surface and draw to that, for double-buffering, like
this:

parent_sf = cairo_get_target(maincanvas_cs); // get parent surface //
drawbuffer_sf = cairo_surface_create_similar(parent_sf,
CAIRO_CONTENT_COLOR_ALPHA, maincanvasWidth, maincanvasHeight);

All of the above exploit the GPU, correct?

Thanks for your time and help!

Christos.

On 10 October 2012 12:08, Chris Wilson <chris at chris-wilson.co.uk> wrote:

> On Wed, 10 Oct 2012 09:20:40 +0300, Christos Sotiriou <csotiriou at gmail.com>
> wrote:
> > Dear Chris, Dear Cairo Developers/Users,
> >
> > I had a few more questions regarding my older post, *i.e.* being able to
> > draw millions of small rectangles on a Cairo surface provided by GTK/GDK.
> >
> > Chris Wilson was kind enough to explain that my Cairo drawing is slow as
> I
> > use a non-integer, non-uniform scaling factor, and has improved the Cairo
> > code for new releases; however, I am stuck with the older Cairo version
> > which I mention in my older email (for O/S compatibility), so I am back
> to
> > probing this issue further, as I really need to speed up zoom-in/zoom-out
> > for my rectangles.
> >
> > My two questions are the following:
> >
> >    1. Does Cairo *always use or not use* 2D Hardware Rendering? How can
> >    this be enabled or verified using Cairo code? If not, where can I
> find a
> >    Cairo code snippet which enables X acceleration?
>
> If you pass cairo an X Drawable, it will use XRender to draw to it.
> If you pass cairo an image buffer, it will render directly to it using
> the CPU.
>
> >    2. As I mention in a prior message I used two methods for
> >    "double-buffering", drawing to an image surface OR drawing to a
> similar
> >    surface (cairo_surface_create_similar). Funnily enough, the latter was
> >    faster. Is there a reason for this? It seems mysterious...
>
> Using image requires doing all the rasterisation locally and transferring
> the final result using PutImage. Using the similar surface, and you will
> offload the rasterisation to the X server, which may in turn use the GPU
> to accelerate the operations.
>
> >    3. Related to my first question, I tried to use Cairo/X interaction to
> >    verify if this would improve drawing, *i.e.* if I used an Xlib
> surface.
> >    I used the following code:
> >
> >     xdisplay = gdk_x11_drawable_get_xdisplay(maincanvas_drawable);
> >     xid = gdk_x11_drawable_get_xid(maincanvas_drawable);
> >     visual =
> >
>  gdk_x11_visual_get_xvisual(gtk_widget_get_visual(GTK_WIDGET(maincanvas)));
> >
> >     maincanvas_sf = cairo_xlib_surface_create(xdisplay, xid, visual,
> >    maincanvasWidth, maincanvasHeight);
> >     maincanvas_cs = cairo_create(maincanvas_sf);
> >
> >    However, drawing to the Xlib surface did not help either (actually
> made
> >    matters worse, as GDK/GTK interaction with scrollbars stopped
> working). So,
> >    coming back to my first question, how can I guarantee 2D acceleration
> and
> >    why is an Xlib surface not helping? How can an Xlib surface be used
> >    properly?
>
> In your expose event, you want to call
>   cr = gdk_cairo_create(gtk_widget_get_window(widget))
> to integrate your drawing into the GTK+ model.
> -Chris
>
> --
> Chris Wilson, Intel Open Source Technology Centre
>



-- 
--------------------------------------------------------------------------
Christos P. Sotiriou
email: csotiriou at gmail.com
Cell: +30 697 8984 222
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