[Mesa-dev] [PATCH 1/3] st/mesa: fix handling of NumSamples=1

[Brian Paul]

We pretty much use the convention that if gl_renderbuffer::NumSamples
or gl_texture_image::NumSamples is zero, it's a non-MSAA surface.
Otherwise, it's an MSAA surface.

This patch changes the sample count checks in st_AllocTextureStorage()
and st_renderbuffer_alloc_storage() to test for samples > 0 instead of > 1.
As it is, if samples==1 we skip the search for the next higher number of
supported samples and ask the gallium driver to create a MSAA surface with
one sample, which no driver supports (AFAIK).  Instead, drivers create a
non-MSAA surface.

A specific example of this problem is the Piglit arb_framebuffer_srgb-blit
test.  It calls glRenderbufferStorageMultisample() with samples=1 to
request an MSAA renderbuffer with the minimum supported number of MSAA
samples.  Instead of creating a 4x or 8x, etc. MSAA surface, we wound up
creating a non-MSAA surface.

Finally, add a comment on the gl_renderbuffer::NumSamples field.

There is one piglit regression with the VMware driver:
ext_framebuffer_multisample-blit-mismatched-formats fails because
now we're actually creating real MSAA surfaces (the requested sample
count is 1) and we're hitting some sort of bug in the blitter code.  That
will have to be fixed separately.  Other drivers may find regressions
too now that MSAA surfaces are really being created.
---
 src/mesa/main/mtypes.h                 | 2 +-
 src/mesa/state_tracker/st_cb_fbo.c     | 3 +--
 src/mesa/state_tracker/st_cb_texture.c | 2 +-
 3 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index 404d586..1dec89c 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -3303,7 +3303,7 @@ struct gl_renderbuffer
     * called without a rb->TexImage.
     */
    GLboolean NeedsFinishRenderTexture;
-   GLubyte NumSamples;
+   GLubyte NumSamples;    /**< zero means not multisampled */
    GLenum InternalFormat; /**< The user-specified format */
    GLenum _BaseFormat;    /**< Either GL_RGB, GL_RGBA, GL_DEPTH_COMPONENT or
                                GL_STENCIL_INDEX. */
diff --git a/src/mesa/state_tracker/st_cb_fbo.c b/src/mesa/state_tracker/st_cb_fbo.c
index 23cbcdc..6986eaa 100644
--- a/src/mesa/state_tracker/st_cb_fbo.c
+++ b/src/mesa/state_tracker/st_cb_fbo.c
@@ -156,9 +156,8 @@ st_renderbuffer_alloc_storage(struct gl_context * ctx,
     *   by the implementation.
     *
     * So let's find the supported number of samples closest to NumSamples.
-    * (NumSamples == 1) is treated the same as (NumSamples == 0).
     */
-   if (rb->NumSamples > 1) {
+   if (rb->NumSamples > 0) {
       unsigned i;
 
       for (i = rb->NumSamples; i <= ctx->Const.MaxSamples; i++) {
diff --git a/src/mesa/state_tracker/st_cb_texture.c b/src/mesa/state_tracker/st_cb_texture.c
index db2913e..de6b57e 100644
--- a/src/mesa/state_tracker/st_cb_texture.c
+++ b/src/mesa/state_tracker/st_cb_texture.c
@@ -2680,7 +2680,7 @@ st_AllocTextureStorage(struct gl_context *ctx,
    bindings = default_bindings(st, fmt);
 
    /* Raise the sample count if the requested one is unsupported. */
-   if (num_samples > 1) {
+   if (num_samples > 0) {
       enum pipe_texture_target ptarget = gl_target_to_pipe(texObj->Target);
       boolean found = FALSE;
 
-- 
1.9.1