Mesa (master): mesa: Clamp some depth values in glClearBufferfv

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Module: Mesa
Branch: master
Commit: 1bf539b3a2129779addde397886870c00045e6d7
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=1bf539b3a2129779addde397886870c00045e6d7

Author: Nanley Chery <nanley.g.chery at intel.com>
Date:   Mon Nov  2 09:02:42 2020 -0800

mesa: Clamp some depth values in glClearBufferfv

OpenGL 3.0 spec, section 4.2.3 "Clearing the Buffers":

   If buffer is DEPTH, drawbuffer must be zero, and value points to the
   single depth value to clear the depth buffer to. Clamping and type
   conversion for fixed-point depth buffers are performed in the same
   fashion as for ClearDepth.

Enables iris to pass the clearbuffer-depth piglit test.

v2. Add spec citation. (Eric Anholt)
v3. Don't clamp floating point formats. (Eric Anholt)

Cc: mesa-stable
Reviewed-by: Marek Olšák <marek.olsak at amd.com>
Reviewed-by: Eric Anholt <eric at anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7410>

---

 src/mesa/main/clear.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/mesa/main/clear.c b/src/mesa/main/clear.c
index ca0ecd95b8c..0a51a868bae 100644
--- a/src/mesa/main/clear.c
+++ b/src/mesa/main/clear.c
@@ -30,6 +30,7 @@
 
 
 
+#include "glformats.h"
 #include "glheader.h"
 #include "clear.h"
 #include "context.h"
@@ -589,7 +590,20 @@ clear_bufferfv(struct gl_context *ctx, GLenum buffer, GLint drawbuffer,
           * hook instead.
           */
          const GLclampd clearSave = ctx->Depth.Clear;
-         ctx->Depth.Clear = *value;
+
+         /* Page 263 (page 279 of the PDF) of the OpenGL 3.0 spec says:
+          *
+          *     "If buffer is DEPTH, drawbuffer must be zero, and value points
+          *     to the single depth value to clear the depth buffer to.
+          *     Clamping and type conversion for fixed-point depth buffers are
+          *     performed in the same fashion as for ClearDepth."
+          */
+         const struct gl_renderbuffer *rb =
+            ctx->DrawBuffer->Attachment[BUFFER_DEPTH].Renderbuffer;
+         const bool is_float_depth =
+            _mesa_has_depth_float_channel(rb->InternalFormat);
+         ctx->Depth.Clear = is_float_depth ? *value : SATURATE(*value);
+
          ctx->Driver.Clear(ctx, BUFFER_BIT_DEPTH);
          ctx->Depth.Clear = clearSave;
       }