videooverlaycomposition: document required map flags

Fix documentation for gst_video_overlay_composition_blend(). The video frame
needs to be mapped with GST_MAP_READWRITE flag.

https://bugzilla.gnome.org/show_bug.cgi?id=771382

diff --git a/gst-libs/gst/video/video-overlay-composition.c b/gst-libs/gst/video/video-overlay-composition.c
index 12e7e077a5f08d4e78ede32289d4027a5262cba9..8e50012f8c3340dcbc5c6b3e3c9742641258a01b 100644 (file)
--- a/gst-libs/gst/video/video-overlay-composition.c
+++ b/gst-libs/gst/video/video-overlay-composition.c
@@ -454,11 +454,15 @@ gst_video_overlay_rectangle_needs_scaling (GstVideoOverlayRectangle * r)
 /**
  * gst_video_overlay_composition_blend:
  * @comp: a #GstVideoOverlayComposition
- * @video_buf: a #GstVideoFrame containing raw video data in a supported format
+ * @video_buf: a #GstVideoFrame containing raw video data in a
+ *             supported format. It should be mapped using GST_MAP_READWRITE
  *
  * Blends the overlay rectangles in @comp on top of the raw video data
  * contained in @video_buf. The data in @video_buf must be writable and
  * mapped appropriately.
+ *
+ * Since @video_buf data is read and will be modified, it ought be
+ * mapped with flag GST_MAP_READWRITE.
  */
 /* FIXME: formats with more than 8 bit per component which get unpacked into
  * ARGB64 or AYUV64 (such as v210, v216, UYVP, GRAY16_LE and GRAY16_BE)