[Mesa-dev] [RFC PATCH] glsl: Allow mixing of GLSL 1.40 and later shader versions.

[Paul Berry]

---

I'm not 100% sure this is the right way to go, and here's why:

Taken together, all the GLSL specs except GLSL 4.30 and GLSL 4.40 tell
a consistent story: desktop shader versions 1.10 and 1.20 may be
linked together, and desktop shader versions 1.40 and above may be
linked together.  No other cross-version linking is allowed.

However, cross-version linking restrictions were explicitly removed in
GLSL 4.30 (the change is listed under "Summary of Changes from Version
4.20 as "Remove cross-version linking restrictions.").  GLSL 4.30 and
4.40 state that *any* version of desktop GLSL may be linked with any
other version of desktop GLSL.  (Note that cross-version linking is
still prohibited for ES shaders).

This leads to a conundrum.  Normally when the GLSL spec changes from
one version to the next, we implement different rules depending on the
user-supplied "#version" directive.  But we can't do that for
cross-version linking rules since it's not clear which version of GLSL
should apply.  Should we:

(a) always follow pre-GLSL 4.30 linking rules, since we don't support
GLSL 4.30 yet?  (that's what this patch implements).

(b) always follow post-GLSL 4.30 linking rules, since they're probably
the clearest reflection of the Khronos board's intent?

(c) make some kind of dynamic determination of which set of rules to
follow?

FWIW, the NVIDIA proprietary driver for Linux (version 313.18) appears
to implement (b).

 src/glsl/linker.cpp | 28 ++++++++++++++++++++--------
 1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
index 9095a40..1dac85c 100644
--- a/src/glsl/linker.cpp
+++ b/src/glsl/linker.cpp
@@ -2057,17 +2057,29 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
       }
    }
 
-   /* Previous to GLSL version 1.30, different compilation units could mix and
-    * match shading language versions.  With GLSL 1.30 and later, the versions
-    * of all shaders must match.
+   /* For desktop GLSL, versions 1.10 and 1.20 may be linked together, and
+    * versions 1.40 and later may be linked together.  But version 1.30 may
+    * not be linked with any other version, and versions prior to 1.30 may not
+    * be linked to versions after 1.30.
     *
     * GLSL ES has never allowed mixing of shading language versions.
     */
-   if ((is_es_prog || max_version >= 130)
-       && min_version != max_version) {
-      linker_error(prog, "all shaders must use same shading "
-		   "language version\n");
-      goto done;
+   if (is_es_prog) {
+      if (min_version != max_version) {
+         linker_error(prog, "all shaders must use same shading "
+                      "language version\n");
+         goto done;
+      }
+   } else {
+      if (min_version < 130 && max_version >= 130) {
+         linker_error(prog, "GLSL versions prior to 1.30 may not be linked "
+                      "with GLSL versions 1.30 and above\n");
+         goto done;
+      } else if (min_version == 130 && max_version > 130) {
+         linker_error(prog, "GLSL version 1.30 may not be linked with GLSL "
+                      "versions above 1.30\n");
+         goto done;
+      }
    }
 
    prog->Version = max_version;
-- 
1.8.4.1