virgl: More info about chosen alignment value

Add more info about why the value of VIRGL_MAP_BUFFER_ALIGNMENT.

Signed-off-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>

diff --git a/src/gallium/drivers/virgl/virgl_screen.h b/src/gallium/drivers/virgl/virgl_screen.h
index 0256d471f2234a8405a2044635ca21a70da367de..93b52b5138d7dab413a9ea45e863e25ac3fcc824 100644 (file)
--- a/src/gallium/drivers/virgl/virgl_screen.h
+++ b/src/gallium/drivers/virgl/virgl_screen.h
@@ -58,6 +58,11 @@ virgl_screen(struct pipe_screen *pipe)
 boolean
 virgl_has_readback_format(struct pipe_screen *screen, enum virgl_formats fmt);
 
+/* GL_ARB_map_buffer_alignment requires 64 as the minimum alignment value.  In
+ * addition to complying with the extension, a high enough alignment value is
+ * expected by various external GL clients. For example, wined3d doesn't like
+ * maps that don't have a 16 byte alignment.
+ */
 #define VIRGL_MAP_BUFFER_ALIGNMENT 64
 
 #endif