st/mesa: bind NULL colorbuffers as specified by glDrawBuffers

An example why it is required:

    Let's say there's a fragment shader writing to gl_FragData[0..1].
    The user calls: glDrawBuffers(2, {GL_NONE, GL_COLOR_ATTACHMENT0});

    That means gl_FragData[0] is unused and gl_FragData[1] is written
    to GL_COLOR_ATTACHMENT0.

st/mesa was skipping the GL_NONE draw buffer, therefore gl_FragData[0]
was written to GL_COLOR_ATTACHMENT0, which was wrong.

This commit fixes it, but drivers must also be fixed not to crash when
binding NULL colorbuffers. There is also a new set of piglit tests for this.

The MSAA state also had to be fixed not to crash when reading fb->cbufs[0].

Reviewed-by: Brian Paul <[email protected]>

1 files changed, 21 insertions, 0 deletions

diff --git a/src/gallium/auxiliary/util/u_framebuffer.c b/src/gallium/auxiliary/util/u_framebuffer.c
index 683967237e9..377b802b62a 100644
--- a/src/gallium/auxiliary/util/u_framebuffer.c
+++ b/src/gallium/auxiliary/util/u_framebuffer.c
@@ -171,3 +171,24 @@ util_framebuffer_get_num_layers(const struct pipe_framebuffer_state *fb)
 	}
 	return num_layers;
 }
+
+
+/**
+ * Return the number of MSAA samples.
+ */
+unsigned
+util_framebuffer_get_num_samples(const struct pipe_framebuffer_state *fb)
+{
+   unsigned i;
+
+   for (i = 0; i < fb->nr_cbufs; i++) {
+      if (fb->cbufs[i]) {
+         return MAX2(1, fb->cbufs[i]->texture->nr_samples);
+      }
+   }
+   if (fb->zsbuf) {
+      return MAX2(1, fb->zsbuf->texture->nr_samples);
+   }
+
+   return 1;
+}