mesa: new assertions, comments about buffer mapping

Since ctx->Driver.MapBuffer() and ctx->Driver.MapBufferRange() may be called
from other places in Mesa (such as VBO) it's important that the driver
callbacks set all the buffer object fields properly (Pointer, Offset, Length,
etc).  Add assertions to make sure that the driver does that.

src/mesa/main/bufferobj.c

@@ -1165,6 +1165,8 @@ _mesa_MapBufferARB(GLenum target, GLenum access)
    GET_CURRENT_CONTEXT(ctx);
    struct gl_buffer_object * bufObj;
    GLbitfield accessFlags;
+   void *map;
+
    ASSERT_OUTSIDE_BEGIN_END_WITH_RETVAL(ctx, NULL);
 
    switch (access) {
@@ -1197,14 +1199,21 @@ _mesa_MapBufferARB(GLenum target, GLenum access)
    }
 
    ASSERT(ctx->Driver.MapBuffer);
-   bufObj->Pointer = ctx->Driver.MapBuffer( ctx, target, access, bufObj );
-   if (!_mesa_bufferobj_mapped(bufObj)) {
+   map = ctx->Driver.MapBuffer( ctx, target, access, bufObj );
+   if (!map) {
       _mesa_error(ctx, GL_OUT_OF_MEMORY, "glMapBufferARB(access)");
    }
 
-   bufObj->AccessFlags = accessFlags;
-   bufObj->Offset = 0;
-   bufObj->Length = bufObj->Size;
+   if (map) {
+      /* The driver callback should have set these fields.
+       * This is important because other modules (like VBO) might call
+       * the driver function directly.
+       */
+      ASSERT(bufObj->Pointer == map);
+      ASSERT(bufObj->Length == bufObj->Size);
+      ASSERT(bufObj->Offset == 0);
+      bufObj->AccessFlags = accessFlags;
+   }
 
    if (access == GL_WRITE_ONLY_ARB || access == GL_READ_WRITE_ARB)
       bufObj->Written = GL_TRUE;
@@ -1455,6 +1464,8 @@ _mesa_MapBufferRange(GLenum target, GLintptr offset, GLsizeiptr length,
 {
    GET_CURRENT_CONTEXT(ctx);
    struct gl_buffer_object *bufObj;
+   void *map;
+
    ASSERT_OUTSIDE_BEGIN_END_WITH_RETVAL(ctx, NULL);
 
    if (!ctx->Extensions.ARB_map_buffer_range) {
@@ -1518,14 +1529,20 @@ _mesa_MapBufferRange(GLenum target, GLintptr offset, GLsizeiptr length,
    }
       
    ASSERT(ctx->Driver.MapBufferRange);
-   bufObj->Pointer = ctx->Driver.MapBufferRange(ctx, target, offset, length,
-                                                access, bufObj);
+   map = ctx->Driver.MapBufferRange(ctx, target, offset, length,
+                                    access, bufObj);
+   if (map) {
+      /* The driver callback should have set all these fields.
+       * This is important because other modules (like VBO) might call
+       * the driver function directly.
+       */
+      ASSERT(bufObj->Pointer == map);
+      ASSERT(bufObj->Length == length);
+      ASSERT(bufObj->Offset == offset);
+      ASSERT(bufObj->AccessFlags == access);
+   }
 
-   bufObj->Offset = offset;
-   bufObj->Length = length;
-   bufObj->AccessFlags = access;
-
-   return bufObj->Pointer;
+   return map;
 }