[Mesa-dev] [PATCHv2 1/3] gallium: add interface to clear buffers

[Roland Scheidegger]

Am 27.03.2014 03:04, schrieb Marek Olšák:
> On Wed, Mar 26, 2014 at 4:30 AM, Roland Scheidegger <sroland at vmware.com> wrote:
>> Am 26.03.2014 03:29, schrieb Marek Olšák:
>>> My reasoning was that it would be better to specify a raw clear value
>>> and clear value size for buffers, which are always untyped, and
>>> pipe_color_union for textures, which are always typed, so that drivers
>>> can easily implement the texture clearing on top of
>>> pipe_context::clear.
>>>
>>> I also suggested that clear_render_target and clear_depth_stencil
>>> should be removed in favor of a new function clear_texture(pipe,
>>> resource, level, box, pipe_color_union). For depth-stencil, we can
>>> assume that the first component of the clear color is a floating-point
>>> depth value and the second component is an unsigned integer stencil
>>> value.
>> This could not clear only depth or stencil, though.
>> Clear is just a mess why couldn't the apis agree a bit more what is
>> useful...
>> So d3d10 can only clear render target / depth stencil views, meaning
>> your resrouces need the bind_render_target flag (not that drivers
>> actually usually enforce this for rendering since it breaks mesa state
>> tracker in a couple of places due to this being not required in general
>> and hard to guess in GL). You cannot clear only parts (or rather, you
>> can clear individual layers and such by creating a different view, but
>> not specify coords). You can however clear only depth or stencil.
>> And you cannot clear buffers (well you can if you make them render
>> target bindable but this has severe limitations and isn't something
>> you'd do just so you can clear them).
>> GL OTOH doesn't require the resources to be renderable for clearing to
>> work, doesn't allow to clear only depth/stencil but does allow a box.
>> There's also another problem with the proposed parameters for d3d10, the
>> format of the resource could be different to that you'd actually want to
>> use for clearing (for typeless resources).
> 
> Adding the format parameter is not a problem. It would also allow
> depth-only or stencil-clear by setting Z24X8 or X24S8, respectively.
Ah yes that should work (I guess though you'd need to be careful with
those "X" values in case of colors format, because I guess for them you
don't want it to mean clearing is skipped).
But, in any case, as long as it can still do what d3d10 requires I'd be
just happy with it.

Roland


> 
> Regarding non-renderable textures, well, RGB9_E5 is the only
> non-renderable GL format on Radeon and we could easily clear that as
> R32_UINT. Radeon drivers already change texture formats to support
> fully-accelerated resource_copy_region and they will do so for
> clearing as well. You can always use a software fallback if you have
> no other option.
> 
> Some of the GL 4.x stuff will be a bigger mess, and there are also fun
> things like GL_ARB_bindless_texture.
> 
> Marek
>