[Mesa-dev] [PATCH 26/35] meta: Use common GLSL code for blits

[Marek Olšák]

On Tue, Feb 4, 2014 at 9:06 PM, Roland Scheidegger <sroland at vmware.com> wrote:
> Am 04.02.2014 13:19, schrieb Marek Olšák:
>> On Tue, Feb 4, 2014 at 10:29 AM, Rogovin, Kevin <kevin.rogovin at intel.com> wrote:
>>>
>>>
>>>> I don't believe our hardware can support GL_ARB_shader_stencil_export.
>>>> The render target write message can take RGBA, depth, and sample masks,
>>>> but not stencil.  Without that, it's not at all obvious how to implement it.
>>>
>>> There is a terrible hack-ish way to do it, but I stress the word terrible and hackish and
>>> it may not work correctly depending on the tile modes and all that fun.
>>>
>>> Here goes. Assuming the depth-stencil is D24S8 we can do this and that the
>>> tile modes work out:
>>>
>>> Bind src depth-stencil as RGBA_8UI, the depth should be in RGB and the stencil in A.
>>> Bind the dst  depth-stencil as RGBA_8UI as well. Fragment shader is simple unfiltered
>>> read and write to dest. If not writing to depth or stencil, mask our RGB or A respectively.
>>>
>>> The above does not handle MSAA->non-MSAA. Going further, it can be done in general
>>> on *paper* with GL_ARB_texture_view if that is extended to allow D24S8 to be on the same
>>> castable category as RGBA_8UI. The main catch is how the tile modes work out, i.e. if the
>>> tile mode for a D24S8 is "compatible" with a RGBA_8UI render target.
>>
>> This is how r300g does it. It blits D24S8 as RGBA_UNORM. Gallium has
>> texture views and it has no limitations on how you can change the
>> format, so it's pretty trivial. r300g changes the format, then calls
>> our "meta" code (u_blitter).
>>
>
> It is not actually obvious this is something which should work in
> gallium in that way. The docs say the format must be "compatible"
> without saying much else (obviously, same number of block bits is a
> requirement). u_format has some function which would check if formats
> are compatible (albeit for a different purpose) and it wouldn't consider
> your example compatible.
> The intention of sampler views is it should allow casting allowed by the
> APIs (d3d10, whatever GL extension).
> The definition of this is definitely loose.

Yeah, it's not very well defined, but that's not important, because
r300g changes the format *internally*, because it knows it can do
that.

Marek