[virglrenderer-devel] [PATCH] virgl: Add method to query supported MSAA samples and positions

[Gert Wollny]

Query the number of supported samples and the sample position and
store these to the caps.v2 structure. We support only up to 16 samples.
This implementation requires a GL host backend.

Signed-off-by: Gert Wollny <gert.wollny at collabora.com>
---
This patch needs another patch against mesa/virgl. 

 src/virgl_hw.h       |  1 +
 src/vrend_formats.c  | 48 +++++++++++++++++++++++++++++++++++++++++++-
 src/vrend_renderer.c |  2 +-
 src/vrend_renderer.h |  3 +++
 4 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/src/virgl_hw.h b/src/virgl_hw.h
index 27b1a25..84bdfaa 100644
--- a/src/virgl_hw.h
+++ b/src/virgl_hw.h
@@ -312,6 +312,7 @@ struct virgl_caps_v2 {
         uint32_t uniform_buffer_offset_alignment;
         uint32_t shader_buffer_offset_alignment;
         uint32_t capability_bits;
+        uint32_t sample_locations[8];
 };
 
 union virgl_caps {
diff --git a/src/vrend_formats.c b/src/vrend_formats.c
index 0bb23c4..d1e18a6 100644
--- a/src/vrend_formats.c
+++ b/src/vrend_formats.c
@@ -467,4 +467,50 @@ bool vrend_is_canonical_format(enum pipe_format format)
    default:
       return false;
    }
-}
\ No newline at end of file
+}
+
+unsigned vrend_renderer_query_multisample_caps(unsigned max_samples, struct virgl_caps_v2 *caps)
+{
+   GLuint tex;
+   GLuint fbo;
+   GLenum status;
+
+   uint i;
+   uint max_samples_confirmed = 1;
+   uint test_num_samples[4] = {2,4,8,16};
+   int offsets[4] = {0,1,2,4};
+
+   glGenTextures( 1, &tex );
+   glGenFramebuffers( 1, &fbo );
+
+   memset(caps->sample_locations, 0, 8 * sizeof(uint32_t));
+
+   for (int i = 0; i < 4 && test_num_samples[i] <= max_samples; ++i) {
+
+      glBindTexture( GL_TEXTURE_2D_MULTISAMPLE, tex );
+      glTexImage2DMultisample( GL_TEXTURE_2D_MULTISAMPLE, test_num_samples[i], GL_RGBA32F, 10, 10, GL_TRUE);
+      status = glGetError();
+
+      if (status == GL_NO_ERROR) {
+         glBindFramebuffer( GL_FRAMEBUFFER, fbo );
+         glFramebufferTexture2D( GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D_MULTISAMPLE, tex, 0 );
+         status = glCheckFramebufferStatus( GL_FRAMEBUFFER );
+         if (status == GL_FRAMEBUFFER_COMPLETE) {
+            max_samples_confirmed = test_num_samples[i];
+
+            for (uint k = 0; k < test_num_samples[i]; ++k) {
+               float msp[2];
+               uint32_t compressed;
+               glGetMultisamplefv(GL_SAMPLE_POSITION, k, msp);
+               compressed = ((unsigned)(floor(msp[0] * 16.0f)) & 0xf) << 4;
+               compressed |= ((unsigned)(floor(msp[1] * 16.0f)) & 0xf);
+               caps->sample_locations[offsets[i] + (k >> 2)] |= compressed  << (8 * (k & 3));
+            }
+         }
+      }
+   }
+
+   glDeleteFramebuffers( 1, &fbo );
+   glDeleteTextures( 1, &tex );
+   return max_samples_confirmed;
+}
diff --git a/src/vrend_renderer.c b/src/vrend_renderer.c
index 8690eb2..7074cad 100644
--- a/src/vrend_renderer.c
+++ b/src/vrend_renderer.c
@@ -7142,7 +7142,7 @@ static bool vrend_renderer_fill_caps_common(uint32_t set, UNUSED uint32_t versio
    caps->v1.max_render_targets = vrend_state.max_draw_buffers;
 
    glGetIntegerv(GL_MAX_SAMPLES, &max);
-   caps->v1.max_samples = max;
+   caps->v1.max_samples = vrend_renderer_query_multisample_caps(max, &caps->v2);
 
 
    /* All of the formats are common. */
diff --git a/src/vrend_renderer.h b/src/vrend_renderer.h
index badf2b1..254edc7 100644
--- a/src/vrend_renderer.h
+++ b/src/vrend_renderer.h
@@ -390,6 +390,9 @@ void vrend_renderer_reset(void);
 int vrend_renderer_get_poll_fd(void);
 void vrend_decode_reset(bool ctx_0_only);
 
+unsigned vrend_renderer_query_multisample_caps(unsigned max_samples,
+                                               struct virgl_caps_v2 *caps);
+
 struct gl_version {
    uint32_t major;
    uint32_t minor;
-- 
2.17.1