[Mesa-dev] [PATCH 03/17] mesa/st: Set _NumSamples in update_framebuffer_state()

[Edward O'Callaghan]

Using PIPE_FORMAT_NONE to indicate what MSAA modes are supported
with a framebuffer using no attachment.

Signed-off-by: Edward O'Callaghan <eocallaghan at alterapraxis.com>
---
 src/mesa/state_tracker/st_atom_framebuffer.c | 51 ++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/src/mesa/state_tracker/st_atom_framebuffer.c b/src/mesa/state_tracker/st_atom_framebuffer.c
index ae883a2..07854ca 100644
--- a/src/mesa/state_tracker/st_atom_framebuffer.c
+++ b/src/mesa/state_tracker/st_atom_framebuffer.c
@@ -64,6 +64,44 @@ update_framebuffer_size(struct pipe_framebuffer_state *framebuffer,
    framebuffer->height = MIN2(framebuffer->height, surface->height);
 }
 
+/**
+ * Round up the requested multisample count to the next supported sample size.
+ */
+static unsigned
+framebuffer_quantize_num_samples(struct pipe_screen *screen, unsigned num_samples)
+{
+   int quantized_samples = 0;
+   bool msaa_mode_supported;
+
+   if (!num_samples)
+      return 0;
+
+   assert(screen);
+
+   /* Assumes the highest supported MSAA is x32 on any hardware */
+   for (unsigned msaa_mode = 32; msaa_mode >= 1; msaa_mode = msaa_mode/2) {
+      assert(!(msaa_mode > 32 || msaa_mode == 0)); /* be safe from int overflows */
+      if (msaa_mode >= num_samples) {
+         /**
+          * For ARB_framebuffer_no_attachment, A format of
+          * PIPE_FORMAT_NONE implies what number of samples is
+          * supported for a framebuffer with no attachment. Thus the
+          * drivers callback must be adjusted for this.
+          */
+         msaa_mode_supported = screen->is_format_supported(screen,
+                                     PIPE_FORMAT_NONE, PIPE_TEXTURE_2D,
+                                     msaa_mode, PIPE_BIND_RENDER_TARGET);
+         /**
+          * Check if the MSAA mode that is higher than the requested
+          * num_samples is supported, and if so returning it.
+          */
+         if (msaa_mode_supported)
+            quantized_samples = msaa_mode;
+      }
+   }
+
+   return quantized_samples;
+}
 
 /**
  * Update framebuffer state (color, depth, stencil, etc. buffers)
@@ -72,6 +110,8 @@ static void
 update_framebuffer_state( struct st_context *st )
 {
    struct pipe_framebuffer_state *framebuffer = &st->state.framebuffer;
+   struct pipe_context *pipe = st->pipe;
+   struct pipe_screen *screen = pipe->screen;
    struct gl_framebuffer *fb = st->ctx->DrawBuffer;
    struct st_renderbuffer *strb;
    GLuint i;
@@ -82,6 +122,17 @@ update_framebuffer_state( struct st_context *st )
    framebuffer->width  = UINT_MAX;
    framebuffer->height = UINT_MAX;
 
+   /**
+    * Quantize the derived default number of samples:
+    *
+    * A query to the driver of supported MSAA values the
+    * hardware supports is done as to legalize the number
+    * of application requested samples, NumSamples.
+    * See commit eb9cf3c for more information.
+    */
+   fb->DefaultGeometry._NumSamples =
+      framebuffer_quantize_num_samples(screen, fb->DefaultGeometry.NumSamples);
+
    /*printf("------ fb size %d x %d\n", fb->Width, fb->Height);*/
 
    /* Examine Mesa's ctx->DrawBuffer->_ColorDrawBuffers state
-- 
2.5.5