2 files changed, 20 insertions, 12 deletions

diff --git a/src/gallium/include/pipe/p_inlines.h b/src/gallium/include/pipe/p_inlines.h
index 4e5252dfbe0..1232c879682 100644
--- a/src/gallium/include/pipe/p_inlines.h
+++ b/src/gallium/include/pipe/p_inlines.h
@@ -85,13 +85,11 @@ pipe_buffer_map_range(struct pipe_screen *screen,
 {
    assert(offset < buf->size);
    assert(offset + length <= buf->size);
+   assert(length);
    if(screen->buffer_map_range)
       return screen->buffer_map_range(screen, buf, offset, length, usage);
-   else {
-      uint8_t *map;
-      map = screen->buffer_map(screen, buf, usage);
-      return map ? map + offset : NULL;
-   }
+   else
+      return screen->buffer_map(screen, buf, usage);
 }
 
 static INLINE void
@@ -102,6 +100,7 @@ pipe_buffer_flush_mapped_range(struct pipe_screen *screen,
 {
    assert(offset < buf->size);
    assert(offset + length <= buf->size);
+   assert(length);
    if(screen->buffer_flush_mapped_range)
       screen->buffer_flush_mapped_range(screen, buf, offset, length);
 }
@@ -116,11 +115,12 @@ pipe_buffer_write(struct pipe_screen *screen,
    
    assert(offset < buf->size);
    assert(offset + size <= buf->size);
-   
+   assert(size);
+
    map = pipe_buffer_map_range(screen, buf, offset, size, PIPE_BUFFER_USAGE_CPU_WRITE);
    assert(map);
    if(map) {
-      memcpy(map, data, size);
+      memcpy(map + offset, data, size);
       pipe_buffer_flush_mapped_range(screen, buf, offset, size);
       pipe_buffer_unmap(screen, buf);
    }
@@ -136,11 +136,12 @@ pipe_buffer_read(struct pipe_screen *screen,
    
    assert(offset < buf->size);
    assert(offset + size <= buf->size);
-   
+   assert(size);
+
    map = pipe_buffer_map_range(screen, buf, offset, size, PIPE_BUFFER_USAGE_CPU_READ);
    assert(map);
    if(map) {
-      memcpy(data, map, size);
+      memcpy(data, map + offset, size);
       pipe_buffer_unmap(screen, buf);
    }
 }
diff --git a/src/gallium/include/pipe/p_screen.h b/src/gallium/include/pipe/p_screen.h
index d7e79ec655e..ed3a026023b 100644
--- a/src/gallium/include/pipe/p_screen.h
+++ b/src/gallium/include/pipe/p_screen.h
@@ -205,8 +205,10 @@ struct pipe_screen {
    /**
     * Map a subrange of the buffer data store into the client's address space.
     *
-    * Return pointer is always relative to offset 0, regardless of the 
-    * read/write ranges.
+    * The returned pointer is always relative to buffer start, regardless of 
+    * the specified range. This is different from the ARB_map_buffer_range
+    * semantics because we don't forbid multiple mappings of the same buffer
+    * (yet).
     */
    void *(*buffer_map_range)( struct pipe_screen *screen,
                               struct pipe_buffer *buf,
@@ -215,7 +217,12 @@ struct pipe_screen {
                               unsigned usage);
 
    /**
-    * written is the range that the client actually wrote. 
+    * Notify a range that was actually written into.
+    * 
+    * The range is relative to the buffer start, regardless of the range 
+    * specified to buffer_map_range. This is different from the 
+    * ARB_map_buffer_range semantics because we don't forbid multiple mappings 
+    * of the same buffer (yet).
     */
    void (*buffer_flush_mapped_range)( struct pipe_screen *screen,
                                       struct pipe_buffer *buf,