[Mesa-dev] [RFC PATCH] mesa/st: don't prematurely optimize for render targets when on virgl
erik.faye-lund at collabora.com
Tue Jul 10 14:01:13 UTC 2018
On 10. juli 2018 15:42, Gert Wollny wrote:
> For three component textures virgl faces the problem that the host driver
> may report that these can not be used as a render target, and when the
> client requests such a texture a four-componet texture will be choosen
> even if only a sampler view was requested. One example where this happens
> is with the Intel i965 driver that doesn't support RGB32* as render target.
> The result is that when allocating a GL_RGB32F and a GL_RGB32I texture, and
> then glCopyImageSubData is called for these two texture, gallium will fail
> with an assertion, because it reports a different per pixel bit count.
> Therefore, when using the virgl driver, don't try to enable BIND_RENDER_TARGET
> for RGB textures that were requested with only BIND_SAMPLER_VIEW.
> Signed-off-by: Gert Wollny <gert.wollny at collabora.com>
> I'm aware that instead of using the device ID, I should probably add a new caps
> flag, but apart from that I was wondering whether there may be better approaches
> to achieve the same goal: The a texture is allocated with the internal format
> as closely as possible to the requested one. Especially it shouldn't change the
> percieved pixel bit count.
> In fact, I was a bit surprised to see that the assertions regarding the
> different sizes was hit in st_copy_image:307 (swizzled_copy). It seems that
> there is some check missing that should redirect the copy in such a case.
> Many thanks for any comments,
> src/mesa/state_tracker/st_format.c | 22 +++++++++++++++-------
> 1 file changed, 15 insertions(+), 7 deletions(-)
> diff --git a/src/mesa/state_tracker/st_format.c b/src/mesa/state_tracker/st_format.c
> index 9ae796eca9..2d8ff756a9 100644
> --- a/src/mesa/state_tracker/st_format.c
> +++ b/src/mesa/state_tracker/st_format.c
> @@ -2285,19 +2285,27 @@ st_ChooseTextureFormat(struct gl_context *ctx, GLenum target,
> /* GL textures may wind up being render targets, but we don't know
> * that in advance. Specify potential render target flags now for formats
> - * that we know should always be renderable.
> + * that we know should always be renderable, except when we are on virgl,
> + * we don't try this for three component textures, because the host might
> + * not support rendering to them, and then Gallium chooses a four component
> + * internal format and calls to e.g. glCopyImageSubData will fail for format
> + * that should be compatible.
> bindings = PIPE_BIND_SAMPLER_VIEW;
> if (_mesa_is_depth_or_stencil_format(internalFormat))
> bindings |= PIPE_BIND_DEPTH_STENCIL;
> - else if (is_renderbuffer || internalFormat == 3 || internalFormat == 4 ||
> - internalFormat == GL_RGB || internalFormat == GL_RGBA ||
> - internalFormat == GL_RGB8 || internalFormat == GL_RGBA8 ||
> + else if (is_renderbuffer ||
> + internalFormat == GL_RGBA ||
> + internalFormat == GL_RGBA8 ||
> internalFormat == GL_BGRA ||
> - internalFormat == GL_RGB16F ||
> internalFormat == GL_RGBA16F ||
> - internalFormat == GL_RGB32F ||
> - internalFormat == GL_RGBA32F)
> + internalFormat == GL_RGBA32F ||
> + ((st->pipe->screen->get_param(st->pipe->screen, PIPE_CAP_DEVICE_ID) != 0x1010) &&
> + (internalFormat == 3 || internalFormat == 4 ||
> + internalFormat == GL_RGB ||
> + internalFormat == GL_RGB8 ||
> + internalFormat == GL_RGB16F ||
> + internalFormat == GL_RGB32F )))
> bindings |= PIPE_BIND_RENDER_TARGET;
I don't think this is correct. The problem is that the spec defines
GL_RGB et al as color-renderable, and in OpenGL any color-renderable
texture can become a render-target at any point. So the driver *has* to
be prepared for rendering to GL_RGB.
The OpenGL 4.6 spec, section 9.4 "Framebuffer completeness" has this to say:
"An internal format is color-renderable if it is RED, RG, RGB, RGBA, or
one of the sized internal formats from table 8.12 whose “CR”
(color-renderable) column is checked in that table"
So, all RGB formats must be color-renderable in OpenGL. For OpenGL ES, I
think this is slightly different, where color-renderable guarantees for
RGB-textures are extensions for at least ES 2.0 IIRC. So *perhaps* we
could get away with something like this for that API.
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