Reicast-emulator: Use EGL_NV_depth_nonlinear for TEGRA3 devices

[ZacharyFoxx]

Tegra 3 has only 16b depth buffer, but has a nice extension to make it less bad. We should enable it, as it is transparent to the rest of the code.

https://www.khronos.org/registry/EGL/extensions/NV/EGL_NV_depth_nonlinear.txt

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Device: Ouya Console
CPU/GPU: TEGRA 3
Android Version: 4.4.4 kitkat
ROM: Lineage OS 11 unofficial
Reicast release: Debugs release 73f3378

Could you improve performance on Tegra 3 platform?
In the description at Play Store, one of the GPUs recommended is the Mali 400. Tegra 3 has equal performance than Mali 400, but the results are different.

For example:
MvsC2 currently run almost without graphical glitches in the stages, like the sky of desert stage. But in Tegra 3, the sky is only a blank blue screen.
Something similar occurs with Soul Calibur: With Mali 400 the stages and characters are almost perfect, but in Tegra 3 we have a lot of glitches and defectives textures.

Both GPUs are OpenGL 2 capable.

---

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[skmp]

Tegra 3 unfortunately dupports only 16bit depth buffer, which often leads
to visual corruption. There’s only so much we can do :(

On Thu, 12 Jul 2018 at 05:01, ZacharyFoxx [e-mail] wrote:

Device: Ouya Console
CPU/GPU: TEGRA 3
Android Version: 4.4.4 kitkat
ROM: Lineage OS 11 unofficial
Reicast release: Debugs release 73f3378
https://github.com/reicast/reicast-emulator/commit/73f3378f5fae4e043d46a666e061b12e1f516e58

Could you improve performance on Tegra 3 platform?
In the description at Play Store, one of the GPUs recommended is the Mali

1. Tegra 3 has equal performance than Mali 400, but the results are
   different.

For example:
MvsC2 currently run almost without graphical glitches in the stages, like
the sky of desert stage. But in Tegra 3, the sky is only a blank blue
screen.
Something similar occurs with Soul Calibur: With Mali 400 the stages and
characters are almost perfect, but in Tegra 3 we have a lot of glitches and
defectives textures.

Both GPUs are OpenGL 2 capable.

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~skmp

[ZacharyFoxx]

After your clarification, I did some searches in the web related with "Tegra 3 depth buffer" and I found other projects which apparently have the same issue and pointing to possible workarounds:

https://devtalk.nvidia.com/default/topic/571706/opengl-es/tegra-3-model-disappearing-issue/
https://www.khronos.org/registry/EGL/extensions/NV/EGL_NV_depth_nonlinear.txt
https://forums.ogre3d.org/viewtopic.php?t=79153
https://stackoverflow.com/questions/11339222/workaround-to-write-depth-buffer-depth-value-in-opengl-es-2-0?rq=1
https://answers.unity.com/questions/342750/tegra-3-issues.html
http://www.jpct.net/wiki/index.php/GPU_guide#Tegra
https://stackoverflow.com/questions/17707638/getting-black-color-from-depth-buffer-in-open-gl-es-2-0

I am not a programmer and I really do not know if anyone of this links could help, but I will really thankful if you could give a look.

[skmp]

@ZacharyFoxx updated the ticket title / desc. to better describe the task that has to be done. Thanks for the research.