Re: opengl and images

[Shai Ayal]

On Mon, Oct 5, 2009 at 10:19 AM, Michael Goffioul
<address@hidden> wrote:
> On Mon, Oct 5, 2009 at 9:12 AM, Søren Hauberg <address@hidden> wrote:
>> man, 05 10 2009 kl. 09:55 +0200, skrev Shai Ayal:
>>> Maybe it's a driver issue? -- what graphics card do you use, and what
>>> is the output of
>>> glxinfo|grep render
>>
>> I'm not sure if you were asking me or Michael, but I have an Intel card,
>> and I get the following form glxinfo
>>
>>        No kernel support for execution fencing, disabling texture
>>        tiling
>>        direct rendering: Yes
>>        OpenGL renderer string: Mesa DRI Mobile Intel® GM45 Express
>>        Chipset GEM 20090712 2009Q2 RC3 x86/MMX/SSE2
>>
>> If you look at the image I sent, you will see that the curve appears
>> under the image, so both objects are rendered. My _guess_ is that the
>> two objects have the same depth, and their order becomes somewhat
>> arbitrary.
>
> Drawing coplanar primitives in OpenGL is not reliable and you can't
> rely on the draw order to put one on top of the other (especially as
> computation is done in float, not double). When dealing with polygons,
> you can use glPolygonOffset, but I'm not sure glDrawPixels is sensitive
> to that setting.

This is very strange, since using plot3 we explicitly asked the line
to be displayed above the z-plane.
This could stem from one of two reasons:
1. Driver bug
2. OpenGL spec alloows for images to be drawn after all other primitives?

I will look into the OpenGL spec later (have to do my real job now...)

Shai