Nouveau - Jun 2019 - Question on interoperability with Nouveau

Hi guys again. A homebrew developer (homebrew is custom software made for
the switch using openGL under nouveau) reported to me that
'glGenerateMipmap'
wasn't working on yuzu (Nintendo Switch emulator). I looked into it and I
noticed all the triangle data used by nouveau to render the mipmaps was all
zeroed out, meaning that probably we don't implement the mechanism you guys
use to upload that data.

How can I track this in your code and know what you guys use to upload the
triangles data into gpu memory ?
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This is done with a sequence of blits, from level 0 -> level 1, then
level 1 -> level 2, etc. st/mesa has a helper which will call the
gallium driver's blit method with the appropriate parameters.

Internally, assuming there's nothing too funky going on, we'll use the
2d blit logic (class 0x902d). If the 3d logic is invoked, it's a
simple shader that textures the source and produces the output. We do
use some funky settings when invoking that shader though -- most
likely thing that you might not have implemented in your emulator is
that we disable VIEWPORT_TRANSFORM_EN, so the coordinates produced by
the vertex shader are non-normalized. We also use enormous coordinates
to draw a single triangle that will cover any possible fb size.

This is the full blit function:
https://cgit.freedesktop.org/mesa/mesa/tree/src/gallium/drivers/nouveau/nvc0/nvc0_surface.c#n1573

The 2d case is handled by nvc0_blit_eng2d, while 3d is handled by
nvc0_blit_3d. The 3d case sets up the rasterizer for the expectations
of the vert and frag shaders, then sticks some data into a cpu-mapped
VBO, and executes it.

Don't worry about the actual shader contents -- they're entirely
unsurprising. But if you're really interested, the fp shader is
generated in nv50/nv50_surface.c.

Hope this helps,

  -ilia

On Thu, Jun 13, 2019 at 9:42 AM Fernando Sahmkow <fsahmkow27 at gmail.com>
wrote:
>
> Hi guys again. A homebrew developer (homebrew is custom software made for
the switch using openGL under nouveau) reported to me that
'glGenerateMipmap' wasn't working on yuzu (Nintendo Switch
emulator). I looked into it and I noticed all the triangle data used by nouveau
to render the mipmaps was all zeroed out, meaning that probably we don't
implement the mechanism you guys use to upload that data.
>
> How can I track this in your code and know what you guys use to upload the
triangles data into gpu memory ?
> _______________________________________________
> Nouveau mailing list
> Nouveau at lists.freedesktop.org
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