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

[Gert Wollny]

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