Drawing CSD on EGL apps

[Bill Spitzak]

I think this problem needs to be solved for putting scrollbars and 
docked panels and all kinds of other graphics around the OpenGL 
viewport. Special-casing window borders is not the solution.

It is true that the solution I have seen on both X and Windows is to 
make a child window and draw the OpenGL into that. This produces all 
kinds of nasty graphics artifacts when windows are resized or internal 
layout changes. I think there will be a need for "subwindows" in Wayland 
(though they are not inside, just stacked, with the shell keeping them 
together). These are going to be needed so the subwindow can have a 
different color space or transform, but it seems wasteful to use this 
for restricting OpenGL.

The other solution that is closer to what I recommend is to use scissor 
and the projection matrix to restrict drawing to a given subrectangle, 
and the client code is just not supposed to do OpenGL calls that will 
break that. On X (and I think on Windows) this has the unfortunate 
side-effect that you have to use OpenGL for *all* drawing in the window. 
It would be nice if wayland (or egl?) fixed this. Another way is to use 
an OpenGL backend for Cairo to draw these parts.

As far as I can tell all large 3D applications (like Maya) either go the 
all-OpenGL route, or they use Qt and subwindows.

In any case I am very wary of any solution that treats the window 
borders as special. The solution must also solve putting scrollbars 
around the openGL or it is not a correct solution. It would be really 
nice if the solution did not require creating otherwise useless extra 
surfaces.

On 11/04/2012 12:10 PM, Giulio Camuffo wrote:
> The problem is not the Qt API but OpenGL. There's no other way of
> translating the contents than telling somehow the offset to the client
> and let the developer accout for it, which is not acceptable.
> Actually, thanks to
> http://doc-snapshot.qt-project.org/5.0/qopenglcontext.html#defaultFramebufferObject a
> FBO solution is doable. But doable only, not good and not optimal at all.
>
> Giulio
>
> 2012/11/4 Bill Spitzak <spitzak at gmail.com <mailto:spitzak at gmail.com>>
>
>     The Qt drawing api should be set with a translation, and possibly
>     with a clip, so that when the contents are drawn into the buffer
>     they are offset correctly to miss the area the window border is
>     drawn into.
>
>
>     On 11/03/2012 04:46 AM, Giulio Camuffo wrote:
>
>         Hi all,
>
>         I'm trying to get decorations in QtWayland for EGL apps. The problem
>         that I'm facing is that I cannot find a good way to do so.
>         One solution could be to use an FBO, let the client draw in that and
>         then draw the content of the FBO into the surface whith its nifty
>         decoration. This would work but what happens if the client in its
>         rendering code calls glBindFramebuffer(0)? It will start drawing
>         directly to the surface and it will screw up badly.
>         Using an EGL pixel buffer would solve the issue, as I can call
>         eglMakeCurrent with that, but copying its content to the surface
>         is slow.
>         A faster thing would probably be wl_egl_pixmap but it's gone.
>
>         The ideal solution would be to have an EGL extension that lets call
>         eglMakeCurrent with a rect that defines the boundaries of the
>         drawable
>         surface.
>         There's NV_post_sub_buffer
>         (http://www.khronos.org/__registry/egl/extensions/NV/__EGL_NV_post_sub_buffer.txt
>         <http://www.khronos.org/registry/egl/extensions/NV/EGL_NV_post_sub_buffer.txt>)
>         but wl_egl_windows don't seem to support it.
>
>         So I'm stuck. Does anyone have an idea?
>
>         Giulio
>
>
>
>         _________________________________________________
>         wayland-devel mailing list
>         wayland-devel at lists.__freedesktop.org
>         <mailto:wayland-devel at lists.freedesktop.org>
>         http://lists.freedesktop.org/__mailman/listinfo/wayland-devel
>         <http://lists.freedesktop.org/mailman/listinfo/wayland-devel>
>
>
>     _________________________________________________
>     wayland-devel mailing list
>     wayland-devel at lists.__freedesktop.org
>     <mailto:wayland-devel at lists.freedesktop.org>
>     http://lists.freedesktop.org/__mailman/listinfo/wayland-devel
>     <http://lists.freedesktop.org/mailman/listinfo/wayland-devel>
>
>
>
>
> _______________________________________________
> wayland-devel mailing list
> wayland-devel at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/wayland-devel
>