# Difference in behaviour between GLX and EGL contect creation

**URL:** <https://discourse.libsdl.org/t/difference-in-behaviour-between-glx-and-egl-contect-creation/21304>\
**Category:** SDL Development\
**Created:** [March 26, 2015, 5:10pm UTC](https://discourse.libsdl.org/t/difference-in-behaviour-between-glx-and-egl-contect-creation/21304 "2015-03-26T17:10:44Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Emmanuel\_Gil\_Peyrot](https://discourse.libsdl.org/letter_avatar_proxy/v4/letter/e/87869e/32.png) [@Emmanuel\_Gil\_Peyrot](https://discourse.libsdl.org/u/Emmanuel_Gil_Peyrot)\
**Post date:** [March 26, 2015, 5:10pm UTC](https://discourse.libsdl.org/t/difference-in-behaviour-between-glx-and-egl-contect-creation/21304/1 "2015-03-26T17:10:44Z")

</div>

Hi,

I noticed a quite trappy difference in the frame buffer configuration  
selection done by the GLX and EGL code. Both emit their wish, as the  
user defined it using SDL\_GL\_SetAttribute, but GLX selects the first  
one, which is the best, and EGL the most fitting.

I noticed that issue because the default is RGB332, which always gave  
me a RGB888 frame buffer on X11, but gave me a RGB565 one on Wayland.

I don?t know what the solution is, maybe removing the code trying to  
find the most fitting configuration from EGL would make the most sense.

I also haven?t checked what the other backends do, for that context  
creation issue.–  
Emmanuel Gil Peyrot  
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<div class="post-metadata">

**Author:** ![Gabriel\_Jacobo](https://discourse.libsdl.org/user_avatar/discourse.libsdl.org/gabriel_jacobo/32/1968_2.png) [@Gabriel\_Jacobo](https://discourse.libsdl.org/u/Gabriel_Jacobo)\
**Post date:** [March 26, 2015, 6:17pm UTC](https://discourse.libsdl.org/t/difference-in-behaviour-between-glx-and-egl-contect-creation/21304/2 "2015-03-26T18:17:48Z")

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2015-03-26 14:10 GMT-03:00 Emmanuel Gil Peyrot :

> Hi,
> 
> I noticed a quite trappy difference in the frame buffer configuration  
> selection done by the GLX and EGL code. Both emit their wish, as the  
> user defined it using SDL\_GL\_SetAttribute, but GLX selects the first  
> one, which is the best, and EGL the most fitting.
> 
> I noticed that issue because the default is RGB332, which always gave  
> me a RGB888 frame buffer on X11, but gave me a RGB565 one on Wayland.
> 
> I don?t know what the solution is, maybe removing the code trying to  
> find the most fitting configuration from EGL would make the most sense.

Why? Trying to find the lowest config that fits the provided parameters is  
the best solution IMO, specially on mobile where every bit counts.

If you really care about getting the same config across backends, you can  
always ask for RGB888.

---

<div class="post-metadata">

**Author:** ![Emmanuel\_Gil\_Peyrot](https://discourse.libsdl.org/letter_avatar_proxy/v4/letter/e/87869e/32.png) [@Emmanuel\_Gil\_Peyrot](https://discourse.libsdl.org/u/Emmanuel_Gil_Peyrot)\
**Post date:** [March 26, 2015, 6:28pm UTC](https://discourse.libsdl.org/t/difference-in-behaviour-between-glx-and-egl-contect-creation/21304/3 "2015-03-26T18:28:21Z")

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> 2015-03-26 14:10 GMT-03:00 Emmanuel Gil Peyrot \<@Emmanuel\_Gil\_Peyrot\>:
> 
> > Hi,
> > 
> > I noticed a quite trappy difference in the frame buffer configuration  
> > selection done by the GLX and EGL code. Both emit their wish, as the  
> > user defined it using SDL\_GL\_SetAttribute, but GLX selects the first  
> > one, which is the best, and EGL the most fitting.
> > 
> > I noticed that issue because the default is RGB332, which always gave  
> > me a RGB888 frame buffer on X11, but gave me a RGB565 one on Wayland.
> > 
> > I don?t know what the solution is, maybe removing the code trying to  
> > find the most fitting configuration from EGL would make the most sense.
> 
> Why? Trying to find the lowest config that fits the provided parameters is  
> the best solution IMO, specially on mobile where every bit counts.

Hmm, I hadn?t thought about mobile, and indeed it makes sense.

It?s quite funny since I think I encountered a bug on GLES, where Mesa  
would unconditionally give me a RGB888 frame buffer instead of the  
selected one.

> If you really care about getting the same config across backends, you can  
> always ask for RGB888.

That?s what I did in my game engine to fix that, no problem.

But this is still an issue of consistency between backends. I would  
suggest backporting the best-fitting code from EGL to GLX, to prevent  
getting a RGB332 frame buffer on some backends and not understanding  
why.On Thu, Mar 26, 2015 at 03:17:48PM -0300, Gabriel Jacobo wrote:

–  
Emmanuel Gil Peyrot  
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