[Mesa-dev] [PATCH v3] virgl: Add support for glGetMultisample

[Erik Faye-Lund]

Unless I'm misunderstanding, this seems to indicate that the hardware
has a fixed set of sample positions, which I don't think is true for
most hardware. Instead, the sample locations is a function of the
multisampling mode for a given surface...

On Thu, Jun 28, 2018 at 3:45 PM Gert Wollny <gert.wollny at collabora.com> wrote:
>
> Use caps to obtain the multisample sample positions for up to 16
> positions and implement the according Gallium interface.
>
> Fixes (when run on GL host):
>     dEQP-GLES31.functional.texture.multisample.samples_1.sample_position
>     dEQP-GLES31.functional.texture.multisample.samples_2.sample_position
>     dEQP-GLES31.functional.texture.multisample.samples_3.sample_position
>     dEQP-GLES31.functional.texture.multisample.samples_4.sample_position
>     dEQP-GLES31.functional.texture.multisample.samples_8.sample_position
>     dEQP-GLES31.functional.texture.multisample.samples_10.sample_position
>     dEQP-GLES31.functional.texture.multisample.samples_12.sample_position
>     dEQP-GLES31.functional.texture.multisample.samples_13.sample_position
>     dEQP-GLES31.functional.texture.multisample.samples_16.sample_position
>
> v2: remove unrelated chunk (thanks Ilia Mirkin)
> v3: - also return positions for intermediate sample counts
>     - fix unused varible warning
>     - update description
>
> Signed-off-by: Gert Wollny <gert.wollny at collabora.com>
> ---
> I left the debug_printf in there, because this patch (together with the
> related virglrenderer patch) is not sufficient to fix above tests on a GLES
> host.
>
>  src/gallium/drivers/virgl/virgl_context.c | 38 +++++++++++++++++++++++++++++++
>  src/gallium/drivers/virgl/virgl_hw.h      |  1 +
>  2 files changed, 39 insertions(+)
>
> diff --git a/src/gallium/drivers/virgl/virgl_context.c b/src/gallium/drivers/virgl/virgl_context.c
> index e6f8dc8525..43c141e42d 100644
> --- a/src/gallium/drivers/virgl/virgl_context.c
> +++ b/src/gallium/drivers/virgl/virgl_context.c
> @@ -920,6 +920,42 @@ virgl_context_destroy( struct pipe_context *ctx )
>     FREE(vctx);
>  }
>
> +static void virgl_get_sample_position(struct pipe_context *ctx,
> +                                      unsigned sample_count,
> +                                      unsigned index,
> +                                      float *out_value)
> +{
> +   struct virgl_context *vctx = virgl_context(ctx);
> +   struct virgl_screen *vs = virgl_screen(vctx->base.screen);
> +
> +   if (sample_count > vs->caps.caps.v1.max_samples) {
> +      debug_printf("VIRGL: requested %d MSAA samples, but only %d supported\n",
> +                   sample_count, vs->caps.caps.v1.max_samples);
> +      return;
> +   }
> +
> +   /* The following is basically copied from dri/i965gen6_get_sample_position
> +    * The only addition is that we hold the msaa positions for all sample
> +    * counts in a flat array. */
> +   uint32_t bits = 0;
> +   if (sample_count == 1) {
> +      out_value[0] = out_value[1] = 0.5f;
> +      return;
> +   } else if (sample_count == 2) {
> +      bits = vs->caps.caps.v2.msaa_sample_positions[0] >> (8 * index);
> +   } else if (sample_count < 4) {
> +      bits = vs->caps.caps.v2.msaa_sample_positions[1] >> (8 * index);
> +   } else if (sample_count < 8) {
> +      bits = vs->caps.caps.v2.msaa_sample_positions[2 + (index >> 2)] >> (8 * (index & 3));
> +   } else if (sample_count < 8) {
> +      bits = vs->caps.caps.v2.msaa_sample_positions[4 + (index >> 2)] >> (8 * (index & 3));
> +   }
> +   out_value[0] = ((bits >> 4) & 0xf) / 16.0f;
> +   out_value[1] = (bits & 0xf) / 16.0f;
> +   debug_printf("VIRGL: sample postion [%2d/%2d] = (%f, %f)\n",
> +                index, sample_count, out_value[0], out_value[1]);
> +}
> +
>  struct pipe_context *virgl_context_create(struct pipe_screen *pscreen,
>                                            void *priv,
>                                            unsigned flags)
> @@ -994,6 +1030,8 @@ struct pipe_context *virgl_context_create(struct pipe_screen *pscreen,
>
>     vctx->base.set_blend_color = virgl_set_blend_color;
>
> +   vctx->base.get_sample_position = virgl_get_sample_position;
> +
>     vctx->base.resource_copy_region = virgl_resource_copy_region;
>     vctx->base.flush_resource = virgl_flush_resource;
>     vctx->base.blit =  virgl_blit;
> diff --git a/src/gallium/drivers/virgl/virgl_hw.h b/src/gallium/drivers/virgl/virgl_hw.h
> index ee58520f9b..82cbb8aed1 100644
> --- a/src/gallium/drivers/virgl/virgl_hw.h
> +++ b/src/gallium/drivers/virgl/virgl_hw.h
> @@ -298,6 +298,7 @@ struct virgl_caps_v2 {
>          uint32_t uniform_buffer_offset_alignment;
>          uint32_t shader_buffer_offset_alignment;
>          uint32_t capability_bits;
> +        uint32_t msaa_sample_positions[8];
>  };
>
>  union virgl_caps {
> --
> 2.16.4
>
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