[Mesa-dev] EGL and glClear(): Nothing is drawn on screen

[Ralf Jung]

Hi list,

first of all, sorry if this is the wrong list for my issue. I tried
various IRC channels, but got no reply, and since I am not actually sure
there is a bug here, I decided to write to a list instead of filing a
bugreport.

My issue is as follows: I wrote a simple GL application which makes it
easy to see tearing. All it does is
* call glClear()
* draw a vertical box as quad
* swap the buffers
* call glFlush()
I wrote it in a way that I can compile it to use either GLX or EGL.
Everything works fine with GLX, but using literally the same code
(except for the initialisation and buffer swap, of course), it does not
work in EGL. Instead of drawing the box, the window stays black. If I
draw a black quad all over the screen instead of calling glClear(), it
works fine even with EGL. I am very new to GL, but from my
understanding, above code should work fine - is there a problem with my
program, or is this a bug in EGL?
You can find the sample program at http://www.ralfj.de/git/gltest.git .
The default behaviour is as described above, calling it with "-o" uses a
black quad instead of glCear().

I am using Debian testing with the current 3.8.6 vanilla kernel. Besides
the mesa 8.0 that comes with Debian, I compiled the 9.0, 9.1 and master
branches of mesa, all with the same result.
My GPU is the one built-in to my Core i5-2450M (I think that's an HD2000).

Kind regards,
Ralf

PS: I am not subscribed to the list, so please keep me in CC.