Move range trimming math into Range class.

Timeline/Sequence_Region.C

@@ -90,9 +90,8 @@ Sequence_Region::trim ( enum trim_e t, int X )
 
 //                td = _r->length - timeline->x_to_ts( 1 );
 
-            _r->offset += td;
-            _r->start  += td;
-            _r->length -= td;
+            _r->trim_left( 0 - td );
+
             break;
         }
         case RIGHT:
@@ -106,9 +105,9 @@ Sequence_Region::trim ( enum trim_e t, int X )
 //            printf( "%li %li\n", td, _r->length - _r->offset );
 
             if ( td >= 0 && _r->length < (nframes_t)td )
-                _r->length = timeline->x_to_ts( 1 );
-            else
-                _r->length -= td;
+                td = _r->length - timeline->x_to_ts( 1 );
+
+            _r->trim_right( 0 - td );
 
             break;
         }

Timeline/Sequence_Widget.H

@@ -40,13 +40,40 @@ struct Drag
     Drag( int X, int Y, nframes_t start=0 ) : x( X ), y( Y ), start( start ) { state = 0; }
 };
 
+/* most common position description. /offset/ is only used by Regions,
+but it's more convenient to have it here  */
 struct Range
 {
     nframes_t start;                       /* where on the timeline */
     nframes_t offset;                      /* first sample from clip */
     nframes_t length;                      /* total number of samples */
+
+    void
+    trim_left ( long n )
+        {
+            start -= n;
+            offset -= n;
+            length += n;
+        }
+
+    void
+    trim_right ( long n )
+        {
+            length += n;
+        }
+};
+
+/* Used by time/tempo points or any other child of Sequence_Widget
+ which must be locked to a point in musical time rather than wallclock
+ time. Bar and beat start at 1. */
+struct BBT
+{
+    unsigned short bar;
+    unsigned char beat;
+    unsigned short tick;
 };
 
+
 /* Base class for virtual widget on a track */
 class Sequence_Widget : public Loggable
 {