From e90e1cc771ac3c660e136db0cdc03e39524da895 Mon Sep 17 00:00:00 2001
From: Carl Hetherington <carl@carlh.net>
Date: Wed, 20 Apr 2011 23:48:39 +0000
Subject: [PATCH] Prevent snap_frame_to_frame returning -ve offset from the
 region start (fixes #3925).

git-svn-id: svn://localhost/ardour2/branches/3.0@9396 d708f5d6-7413-0410-9779-e7cbd77b26cf
---
 gtk2_ardour/midi_region_view.cc | 28 ++++++++++++++++++++++------
 gtk2_ardour/midi_region_view.h  |  6 +-----
 2 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/gtk2_ardour/midi_region_view.cc b/gtk2_ardour/midi_region_view.cc
index 9be06cb1b7..7b9bb4ae30 100644
--- a/gtk2_ardour/midi_region_view.cc
+++ b/gtk2_ardour/midi_region_view.cc
@@ -2238,14 +2238,30 @@ MidiRegionView::snap_pixel_to_frame(double x)
 	return frame - _region->position(); // convert back to region relative
 }
 
-framepos_t
-MidiRegionView::snap_frame_to_frame(framepos_t x)
+/** Snap a frame offset within our region using the current snap settings.
+ *  @param x Frame offset from this region's position.
+ *  @return Snapped frame offset from this region's position.
+ */
+frameoffset_t
+MidiRegionView::snap_frame_to_frame (frameoffset_t x)
 {
 	PublicEditor& editor = trackview.editor();
-	// x is region relative, convert it to global absolute frames
-	framepos_t frame = x + _region->position();
-	editor.snap_to(frame);
-	return frame - _region->position(); // convert back to region relative
+
+	/* x is region relative, convert it to global absolute frames */
+	framepos_t const session_frame = x + _region->position();
+
+	/* try a snap in either direction */
+	framepos_t frame = session_frame;
+	editor.snap_to (frame, 0);
+
+	/* if we went off the beginning of the region, snap forwards */
+	if (frame < _region->position ()) {
+		frame = session_frame;
+		editor.snap_to (frame, 1);
+	}
+
+	/* back to region relative */
+	return frame - _region->position();
 }
 
 double
diff --git a/gtk2_ardour/midi_region_view.h b/gtk2_ardour/midi_region_view.h
index ccd6a82dec..97cc07b7e2 100644
--- a/gtk2_ardour/midi_region_view.h
+++ b/gtk2_ardour/midi_region_view.h
@@ -250,11 +250,7 @@ class MidiRegionView : public RegionView
 	 */
 	framepos_t snap_pixel_to_frame(double x);
 
-	/** Snap a region relative frame coordinate to frame units.
-	 * @param x a pixel coordinate relative to region start
-	 * @return the snapped framepos_t coordinate relative to region start
-	 */
-	framepos_t snap_frame_to_frame(framepos_t x);
+	ARDOUR::frameoffset_t snap_frame_to_frame (ARDOUR::frameoffset_t);
 
 	/** Convert a timestamp in beats to frames (both relative to region start) */
 	framepos_t beats_to_frames(double beats) const;