Mesa (7.9): mesa: make glIsBuffer() return false for never bound buffers

[Brian Paul]

Module: Mesa
Branch: 7.9
Commit: 3e4ed3879102878ee880d739e17253ce4ab789be
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=3e4ed3879102878ee880d739e17253ce4ab789be

Author: Brian Paul <brianp at vmware.com>
Date:   Mon Nov 15 08:47:38 2010 -0700

mesa: make glIsBuffer() return false for never bound buffers

Use a dummy buffer object as we do for frame/renderbuffer objects.
Fixes http://bugs.freedesktop.org/show_bug.cgi?id=31514

Note: this is a candidate for the 7.9 branch.
(cherry picked from commit c552f273f559968dfd770367e25329baccbcd0c4)

---

 src/mesa/main/bufferobj.c |   32 ++++++++++++++++++--------------
 1 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/src/mesa/main/bufferobj.c b/src/mesa/main/bufferobj.c
index 4797f29..967bdf9 100644
--- a/src/mesa/main/bufferobj.c
+++ b/src/mesa/main/bufferobj.c
@@ -55,6 +55,13 @@
 
 
 /**
+ * Used as a placeholder for buffer objects between glGenBuffers() and
+ * glBindBuffer() so that glIsBuffer() can work correctly.
+ */
+static struct gl_buffer_object DummyBufferObject;
+
+
+/**
  * Return pointer to address of a buffer object target.
  * \param ctx  the GL context
  * \param target  the buffer object target to be retrieved.
@@ -554,6 +561,9 @@ _mesa_copy_buffer_subdata(GLcontext *ctx,
 void
 _mesa_init_buffer_objects( GLcontext *ctx )
 {
+   memset(&DummyBufferObject, 0, sizeof(DummyBufferObject));
+   DummyBufferObject.RefCount = 1000*1000*1000; /* never delete */
+
    _mesa_reference_buffer_object(ctx, &ctx->Array.ArrayBufferObj,
                                  ctx->Shared->NullBufferObj);
    _mesa_reference_buffer_object(ctx, &ctx->Array.ElementArrayBufferObj,
@@ -611,8 +621,10 @@ bind_buffer_object(GLcontext *ctx, GLenum target, GLuint buffer)
    else {
       /* non-default buffer object */
       newBufObj = _mesa_lookup_bufferobj(ctx, buffer);
-      if (!newBufObj) {
-         /* if this is a new buffer object id, allocate a buffer object now */
+      if (!newBufObj || newBufObj == &DummyBufferObject) {
+         /* If this is a new buffer object id, or one which was generated but
+          * never used before, allocate a buffer object now.
+          */
          ASSERT(ctx->Driver.NewBufferObject);
          newBufObj = ctx->Driver.NewBufferObject(ctx, buffer, target);
          if (!newBufObj) {
@@ -1072,18 +1084,10 @@ _mesa_GenBuffersARB(GLsizei n, GLuint *buffer)
 
    first = _mesa_HashFindFreeKeyBlock(ctx->Shared->BufferObjects, n);
 
-   /* Allocate new, empty buffer objects and return identifiers */
+   /* Insert the ID and pointer to dummy buffer object into hash table */
    for (i = 0; i < n; i++) {
-      struct gl_buffer_object *bufObj;
-      GLuint name = first + i;
-      GLenum target = 0;
-      bufObj = ctx->Driver.NewBufferObject( ctx, name, target );
-      if (!bufObj) {
-         _glthread_UNLOCK_MUTEX(ctx->Shared->Mutex);
-         _mesa_error(ctx, GL_OUT_OF_MEMORY, "glGenBuffersARB");
-         return;
-      }
-      _mesa_HashInsert(ctx->Shared->BufferObjects, first + i, bufObj);
+      _mesa_HashInsert(ctx->Shared->BufferObjects, first + i,
+                       &DummyBufferObject);
       buffer[i] = first + i;
    }
 
@@ -1109,7 +1113,7 @@ _mesa_IsBufferARB(GLuint id)
    bufObj = _mesa_lookup_bufferobj(ctx, id);
    _glthread_UNLOCK_MUTEX(ctx->Shared->Mutex);
 
-   return bufObj ? GL_TRUE : GL_FALSE;
+   return bufObj && bufObj != &DummyBufferObject;
 }