i965: Comment gen6_hiz_get_framebuffer_enum()

Make the comments precise. Explain why each branch is needed and correct.
Document the potential pitfall in the true-branch.

Signed-off-by: Chad Versace <[email protected]>

1 files changed, 6 insertions, 4 deletions

diff --git a/src/mesa/drivers/dri/i965/gen6_hiz.c b/src/mesa/drivers/dri/i965/gen6_hiz.c
index 92b1d61ef44..4d36729e7c5 100644
--- a/src/mesa/drivers/dri/i965/gen6_hiz.c
+++ b/src/mesa/drivers/dri/i965/gen6_hiz.c
@@ -114,14 +114,16 @@ gen6_hiz_get_framebuffer_enum(struct gl_context *ctx,
                               GLenum *bind_enum,
                               GLenum *get_enum)
 {
-   /* If the blit framebuffer extension isn't supported then Mesa will
-      report an error if we try to bind GL_DRAW_FRAMEBUFFER. However in
-      that case it should be safe to just save and restore
-      GL_FRAMEBUFFER instead. */
    if (ctx->Extensions.EXT_framebuffer_blit && ctx->API == API_OPENGL) {
+      /* Different buffers may be bound to GL_DRAW_FRAMEBUFFER and
+       * GL_READ_FRAMEBUFFER. Take care to not disrupt the read buffer.
+       */
       *bind_enum = GL_DRAW_FRAMEBUFFER;
       *get_enum = GL_DRAW_FRAMEBUFFER_BINDING;
    } else {
+      /* The enums GL_DRAW_FRAMEBUFFER and GL_READ_FRAMEBUFFER do not exist.
+       * The bound framebuffer is both the read and draw buffer.
+       */
       *bind_enum = GL_FRAMEBUFFER;
       *get_enum = GL_FRAMEBUFFER_BINDING;
    }