[Mesa-dev] [PATCH 4/4] glsl: Disallow relinking if a program is used by an active XFB object.

[Kenneth Graunke]

Paused transform feedback objects may refer to a program other than the
current program.  If any active objects refer to a program, LinkProgram
must reject the request to relink.

The code to detect this is ugly since _mesa_HashWalk is awkward to use,
but unfortunately we can't use hash_table_foreach since there's no way
to get at the underlying struct hash_table (and even then, we'd need to
handle locking somehow).

Fixes the last subcase of Piglit's new ARB_transform_feedback2
api-errors test.

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/main/shaderapi.c         | 16 +++++++++-------
 src/mesa/main/transformfeedback.c | 35 +++++++++++++++++++++++++++++++++++
 src/mesa/main/transformfeedback.h |  4 ++++
 3 files changed, 48 insertions(+), 7 deletions(-)

diff --git a/src/mesa/main/shaderapi.c b/src/mesa/main/shaderapi.c
index 4fe9d9c..30aa83c 100644
--- a/src/mesa/main/shaderapi.c
+++ b/src/mesa/main/shaderapi.c
@@ -42,6 +42,7 @@
 #include "main/dispatch.h"
 #include "main/enums.h"
 #include "main/hash.h"
+#include "main/hash_table.h"
 #include "main/mtypes.h"
 #include "main/shaderapi.h"
 #include "main/shaderobj.h"
@@ -812,19 +813,20 @@ static void
 link_program(struct gl_context *ctx, GLuint program)
 {
    struct gl_shader_program *shProg;
-   struct gl_transform_feedback_object *obj =
-      ctx->TransformFeedback.CurrentObject;
+   struct gl_transform_feedback_object *obj;
 
    shProg = _mesa_lookup_shader_program_err(ctx, program, "glLinkProgram");
    if (!shProg)
       return;
 
-   if (obj->Active
-       && (shProg == ctx->Shader.CurrentVertexProgram
-	   || shProg == ctx->Shader.CurrentGeometryProgram
-	   || shProg == ctx->Shader.CurrentFragmentProgram)) {
+   /* From the ARB_transform_feedback2 specification:
+    * "The error INVALID_OPERATION is generated by LinkProgram if <program> is
+    *  the name of a program being used by one or more transform feedback
+    *  objects, even if the objects are not currently bound or are paused."
+    */
+   if (_mesa_transform_feedback_is_using_program(ctx, shProg)) {
       _mesa_error(ctx, GL_INVALID_OPERATION,
-                  "glLinkProgram(transform feedback active)");
+                  "glLinkProgram(transform feedback is using the program)");
       return;
    }
 
diff --git a/src/mesa/main/transformfeedback.c b/src/mesa/main/transformfeedback.c
index 191e88c..bc9b52a 100644
--- a/src/mesa/main/transformfeedback.c
+++ b/src/mesa/main/transformfeedback.c
@@ -44,6 +44,41 @@
 
 #include "program/prog_parameter.h"
 
+struct using_program_tuple
+{
+   struct gl_shader_program *shProg;
+   bool found;
+};
+
+static void
+active_xfb_object_references_program(GLuint key, void *data, void *user_data)
+{
+   struct using_program_tuple *callback_data = user_data;
+   struct gl_transform_feedback_object *obj = data;
+   if (obj->Active && obj->shader_program == callback_data->shProg)
+      callback_data->found = true;
+}
+
+/**
+ * Return true if any active transform feedback object is using a program.
+ */
+bool
+_mesa_transform_feedback_is_using_program(struct gl_context *ctx,
+                                          struct gl_shader_program *shProg)
+{
+   struct using_program_tuple callback_data;
+   callback_data.shProg = shProg;
+   callback_data.found = false;
+
+   _mesa_HashWalk(ctx->TransformFeedback.Objects,
+                  active_xfb_object_references_program, &callback_data);
+
+   /* Also check DefaultObject, as it's not in the Objects hash table. */
+   active_xfb_object_references_program(0, ctx->TransformFeedback.DefaultObject,
+                                        &callback_data);
+
+   return callback_data.found;
+}
 
 /**
  * Do reference counting of transform feedback buffers.
diff --git a/src/mesa/main/transformfeedback.h b/src/mesa/main/transformfeedback.h
index f6dc2a7..0ffaab5 100644
--- a/src/mesa/main/transformfeedback.h
+++ b/src/mesa/main/transformfeedback.h
@@ -120,4 +120,8 @@ _mesa_is_xfb_active_and_unpaused(const struct gl_context *ctx)
       !ctx->TransformFeedback.CurrentObject->Paused;
 }
 
+extern bool
+_mesa_transform_feedback_is_using_program(struct gl_context *ctx,
+                                          struct gl_shader_program *shProg);
+
 #endif /* TRANSFORM_FEEDBACK_H */
-- 
1.8.3.4