i965/gen6: Initial implementation of MSAA.

This patch enables MSAA for Gen6, by modifying intel_mipmap_tree to
understand multisampled buffers, adapting the rendering pipeline setup
to enable multisampled rendering, and adding multisample resolve
operations to brw_blorp_blit.cpp. Some preparation work is also
included for Gen7, but it is not yet enabled.

MSAA support is still fairly preliminary.  In particular, the
following are not yet supported:
- Fully general blits between MSAA and non-MSAA buffers.
- Formats other than RGBA8, DEPTH24, and STENCIL8.
- Centroid interpolation.
- Coverage parameters (glSampleCoverage, GL_SAMPLE_ALPHA_TO_COVERAGE,
  GL_SAMPLE_ALPHA_TO_ONE, GL_SAMPLE_COVERAGE, GL_SAMPLE_COVERAGE_VALUE,
  GL_SAMPLE_COVERAGE_INVERT).

Fixes piglit tests "EXT_framebuffer_multisample/accuracy" on
i965/Gen6.

v2:
- In intel_alloc_renderbuffer_storage(), quantize the requested number
  of samples to the next higher sample count supported by the
  hardware.  This ensures that a query of GL_SAMPLES will return the
  correct value.  It also ensures that MSAA is fully disabled on Gen7
  for now (since Gen7 MSAA support doesn't work yet).
- When reading from a non-MSAA surface, ensure that s_is_zero is true
  so that we won't try to read from a nonexistent sample.

1 files changed, 28 insertions, 3 deletions

diff --git a/src/mesa/drivers/dri/intel/intel_fbo.c b/src/mesa/drivers/dri/intel/intel_fbo.c
index f92d78f378a..bbd5f6652e9 100644
--- a/src/mesa/drivers/dri/intel/intel_fbo.c
+++ b/src/mesa/drivers/dri/intel/intel_fbo.c
@@ -189,6 +189,29 @@ intel_unmap_renderbuffer(struct gl_context *ctx,
 
 
 /**
+ * Round up the requested multisample count to the next supported sample size.
+ */
+static unsigned
+quantize_num_samples(struct intel_context *intel, unsigned num_samples)
+{
+   switch (intel->gen) {
+   case 6:
+      /* Gen6 supports only 4x multisampling. */
+      if (num_samples > 0)
+         return 4;
+      else
+         return 0;
+   case 7:
+      /* TODO: MSAA only implemented on Gen6 */
+      return 0;
+   default:
+      /* MSAA unsupported */
+      return 0;
+   }
+}
+
+
+/**
  * Called via glRenderbufferStorageEXT() to set the format and allocate
  * storage for a user-created renderbuffer.
  */
@@ -199,6 +222,7 @@ intel_alloc_renderbuffer_storage(struct gl_context * ctx, struct gl_renderbuffer
 {
    struct intel_context *intel = intel_context(ctx);
    struct intel_renderbuffer *irb = intel_renderbuffer(rb);
+   rb->NumSamples = quantize_num_samples(intel, rb->NumSamples);
 
    ASSERT(rb->Name != 0);
 
@@ -241,12 +265,13 @@ intel_alloc_renderbuffer_storage(struct gl_context * ctx, struct gl_renderbuffer
       return true;
 
    irb->mt = intel_miptree_create_for_renderbuffer(intel, rb->Format,
-						   width, height);
+						   width, height,
+                                                   rb->NumSamples);
    if (!irb->mt)
       return false;
 
    if (intel->vtbl.is_hiz_depth_format(intel, rb->Format)) {
-      bool ok = intel_miptree_alloc_hiz(intel, irb->mt);
+      bool ok = intel_miptree_alloc_hiz(intel, irb->mt, rb->NumSamples);
       if (!ok) {
 	 intel_miptree_release(&irb->mt);
 	 return false;
@@ -495,7 +520,7 @@ intel_renderbuffer_update_wrapper(struct intel_context *intel,
 
    if (mt->hiz_mt == NULL &&
        intel->vtbl.is_hiz_depth_format(intel, rb->Format)) {
-      intel_miptree_alloc_hiz(intel, mt);
+      intel_miptree_alloc_hiz(intel, mt, 0 /* num_samples */);
       if (!mt->hiz_mt)
 	 return false;
    }