From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-0.9 required=5.0 tests=BAYES_00,FORGED_GMAIL_RCVD,
	FREEMAIL_FROM autolearn=no autolearn_force=no version=3.4.4
X-Received: by 2002:ac8:4809:: with SMTP id g9mr24912712qtq.33.1589325309478;
        Tue, 12 May 2020 16:15:09 -0700 (PDT)
X-Received: by 2002:aca:816:: with SMTP id 22mr24372858oii.51.1589325308650;
 Tue, 12 May 2020 16:15:08 -0700 (PDT)
Path: 
 eternal-september.org!reader01.eternal-september.org!feeder.eternal-september.org!news.gegeweb.eu!gegeweb.org!usenet-fr.net!proxad.net!feeder1-2.proxad.net!209.85.160.216.MISMATCH!news-out.google.com!nntp.google.com!postnews.google.com!google-groups.googlegroups.com!not-for-mail
Newsgroups: comp.lang.ada
Date: Tue, 12 May 2020 16:15:08 -0700 (PDT)
Complaints-To: groups-abuse@google.com
Injection-Info: google-groups.googlegroups.com; posting-host=208.114.128.69;
 posting-account=MRPdDAoAAADUJmZVjnYaoafXFMadSeY1
NNTP-Posting-Host: 208.114.128.69
User-Agent: G2/1.0
MIME-Version: 1.0
Message-ID: <705052ba-5cff-46af-a28c-1e25e60e2eef@googlegroups.com>
Subject: Xlib, (GLX or EGL),
 OpenGL. Stuck at double buffering not working properly.
From: Olivier Henley <olivier.henley@gmail.com>
Injection-Date: Tue, 12 May 2020 23:15:09 +0000
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Xref: reader01.eternal-september.org comp.lang.ada:58668
Date: 2020-05-12T16:15:08-07:00
List-Id: <comp.lang.ada>

Hi to all,

In my spare time I am working on a cross-platform windowing lib for OpenGL =
in Ada.=20

In a nutshell, a GLFW replacement.

I come to you because on Linux, wrapping, and driving Xlib with GLX or EGL =
in Ada, I am failing to get double buffering to work.=20

Generally its working, eg. I get sample code from OpenGLAda rendering fine =
in the window but if I try to resize a window rapidly, I get black tearing =
and sometimes dropped frames. I did fix this problem on windows by threadin=
g the rendering out of the window message pump, but for Linux, threading ov=
er X11 makes things explode. I looked into XInitThread but the documentatio=
n leave me cold.

I tried two other Ada projects that paint some OpenGL in a native Linux win=
dow using (Xlib and GLX) namely Globe3D and AdaOGL. Both suffer from the sa=
me tearing and/or dropped frame when resizing the window.

Now if I compile an equivalent simple GLFW C example code, it works like a =
charm, no dropped frame, no tearing. I looked at their code and they do not=
 seem to make much more than I do. I also found, compiled, and tried a real=
ly simple C source code file using Xlib/GLX and it works. (http://andrewd.c=
es.clemson.edu/courses/graphics/examples/glx-simple/glxsimple.c)

Anyone is aware of what is going on here? Something special about the Ada r=
untime that I should know about or is it just me that does not handle the X=
lib window message pump incorrectly?

Any insights welcome.

Thanks,

Olivier=20

Note: Now because the threading problem over X11 looks like mostly coming f=
rom the whole needed 'same thread context for window and GL' I was thinking=
 rendering GL to a double buffer of Pixmaps/pBuffer (XLib off-screen render=
 targets) from a separate thread and then just blit myself to the window at=
 the 'Expose' events. Make sense, any thoughts on that?