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

[Jose Fonseca]

----- Original Message -----
> 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.
> 
> 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.

Having a clear_resource, with all necessary parameters so it can superceed clear_render/depth_stencil view, seems a sensible thing to do FWIW.

Jose