VSE: Use snapping settings for scrubbing

Use "Snap Playhead to Strips" option to enable playhead snapping.
Change behavior of CTRL key to invert snapping similar to transform operator.

Currently this option is disabled by default. It makes editing quite unpleasant
for me personally, but ideally I should gather feedback from more users.

Reviewed By: campbellbarton

Differential Revision: https://developer.blender.org/D11745

4 files changed, 86 insertions, 5 deletions

diff --git a/release/scripts/startup/bl_ui/space_sequencer.py b/release/scripts/startup/bl_ui/space_sequencer.py
index 5e92e088b36..55714e0b0a5 100644
--- a/release/scripts/startup/bl_ui/space_sequencer.py
+++ b/release/scripts/startup/bl_ui/space_sequencer.py
@@ -2293,6 +2293,9 @@ class SEQUENCER_PT_snapping(Panel):
         col.prop(sequencer_tool_settings, "snap_ignore_muted", text="Muted Strips")
         col.prop(sequencer_tool_settings, "snap_ignore_sound", text="Sound Strips")
 
+        col = layout.column()
+        col.prop(sequencer_tool_settings, "use_snap_current_frame_to_strips")
+
 
 classes = (
     SEQUENCER_MT_change,
diff --git a/source/blender/editors/animation/anim_ops.c b/source/blender/editors/animation/anim_ops.c
index 73b9b118148..6f3277397c5 100644
--- a/source/blender/editors/animation/anim_ops.c
+++ b/source/blender/editors/animation/anim_ops.c
@@ -51,8 +51,10 @@
 
 #include "DEG_depsgraph.h"
 
+#include "SEQ_iterator.h"
 #include "SEQ_sequencer.h"
 #include "SEQ_time.h"
+#include "SEQ_transform.h"
 
 #include "anim_intern.h"
 
@@ -81,6 +83,49 @@ static bool change_frame_poll(bContext *C)
   return false;
 }
 
+static int seq_snap_threshold_get_frame_distance(bContext *C)
+{
+  const int snap_distance = SEQ_tool_settings_snap_distance_get(CTX_data_scene(C));
+  const ARegion *region = CTX_wm_region(C);
+  return round_fl_to_int(UI_view2d_region_to_view_x(&region->v2d, snap_distance) -
+                         UI_view2d_region_to_view_x(&region->v2d, 0));
+}
+
+static void seq_frame_snap_update_best(const int position,
+                                       const int timeline_frame,
+                                       int *r_best_frame,
+                                       int *r_best_distance)
+{
+  if (abs(position - timeline_frame) < *r_best_distance) {
+    *r_best_distance = abs(position - timeline_frame);
+    *r_best_frame = position;
+  }
+}
+
+static int seq_frame_apply_snap(bContext *C, Scene *scene, const int timeline_frame)
+{
+
+  ListBase *seqbase = SEQ_active_seqbase_get(SEQ_editing_get(scene, false));
+  SeqCollection *strips = SEQ_query_all_strips(seqbase);
+
+  int best_frame = 0;
+  int best_distance = MAXFRAME;
+  Sequence *seq;
+  SEQ_ITERATOR_FOREACH (seq, strips) {
+    seq_frame_snap_update_best(
+        SEQ_transform_get_left_handle_frame(seq), timeline_frame, &best_frame, &best_distance);
+    seq_frame_snap_update_best(
+        SEQ_transform_get_right_handle_frame(seq), timeline_frame, &best_frame, &best_distance);
+  }
+  SEQ_collection_free(strips);
+
+  if (best_distance < seq_snap_threshold_get_frame_distance(C)) {
+    return best_frame;
+  }
+
+  return timeline_frame;
+}
+
 /* Set the new frame number */
 static void change_frame_apply(bContext *C, wmOperator *op)
 {
@@ -90,7 +135,7 @@ static void change_frame_apply(bContext *C, wmOperator *op)
 
   if (do_snap) {
     if (CTX_wm_space_seq(C)) {
-      frame = SEQ_time_find_next_prev_edit(scene, frame, SEQ_SIDE_BOTH, true, false, false);
+      frame = seq_frame_apply_snap(C, scene, frame);
     }
     else {
       frame = BKE_scene_frame_snap_by_seconds(scene, 1.0, frame);
@@ -181,6 +226,18 @@ static void change_frame_seq_preview_end(bContext *C)
   }
 }
 
+static bool use_sequencer_snapping(bContext *C)
+{
+  if (!CTX_wm_space_seq(C)) {
+    return false;
+  }
+
+  Scene *scene = CTX_data_scene(C);
+  short snap_flag = SEQ_tool_settings_snap_flag_get(scene);
+  return (scene->toolsettings->snap_flag & SCE_SNAP_SEQ) &&
+         (snap_flag & SEQ_SNAP_CURRENT_FRAME_TO_STRIPS);
+}
+
 /* Modal Operator init */
 static int change_frame_invoke(bContext *C, wmOperator *op, const wmEvent *event)
 {
@@ -190,6 +247,10 @@ static int change_frame_invoke(bContext *C, wmOperator *op, const wmEvent *event
    */
   RNA_float_set(op->ptr, "frame", frame_from_event(C, event));
 
+  if (use_sequencer_snapping(C)) {
+    RNA_boolean_set(op->ptr, "snap", true);
+  }
+
   change_frame_seq_preview_begin(C, event);
 
   change_frame_apply(C, op);
@@ -231,11 +292,22 @@ static int change_frame_modal(bContext *C, wmOperator *op, const wmEvent *event)
 
     case EVT_LEFTCTRLKEY:
     case EVT_RIGHTCTRLKEY:
-      if (event->val == KM_RELEASE) {
-        RNA_boolean_set(op->ptr, "snap", false);
+      /* Use Ctrl key to invert snapping in sequencer. */
+      if (use_sequencer_snapping(C)) {
+        if (event->val == KM_RELEASE) {
+          RNA_boolean_set(op->ptr, "snap", true);
+        }
+        else if (event->val == KM_PRESS) {
+          RNA_boolean_set(op->ptr, "snap", false);
+        }
       }
-      else if (event->val == KM_PRESS) {
-        RNA_boolean_set(op->ptr, "snap", true);
+      else {
+        if (event->val == KM_RELEASE) {
+          RNA_boolean_set(op->ptr, "snap", false);
+        }
+        else if (event->val == KM_PRESS) {
+          RNA_boolean_set(op->ptr, "snap", true);
+        }
       }
       break;
   }
diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index 5fc6cdf58a3..cd752b220a3 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -2069,6 +2069,7 @@ enum {
 /** #SequencerToolSettings.snap_flag */
 #define SEQ_SNAP_IGNORE_MUTED (1 << 0)
 #define SEQ_SNAP_IGNORE_SOUND (1 << 1)
+#define SEQ_SNAP_CURRENT_FRAME_TO_STRIPS (1 << 2)
 
 /** #ToolSettings.snap_node_mode */
 #define SCE_SNAP_MODE_NODE_X (1 << 0)
diff --git a/source/blender/makesrna/intern/rna_scene.c b/source/blender/makesrna/intern/rna_scene.c
index cb1b0dbd1e5..0a91d5f01bc 100644
--- a/source/blender/makesrna/intern/rna_scene.c
+++ b/source/blender/makesrna/intern/rna_scene.c
@@ -3535,6 +3535,11 @@ static void rna_def_sequencer_tool_settings(BlenderRNA *brna)
   RNA_def_property_boolean_sdna(prop, NULL, "snap_flag", SEQ_SNAP_IGNORE_SOUND);
   RNA_def_property_ui_text(prop, "Ignore Sound Strips", "Don't snap to sound strips");
 
+  prop = RNA_def_property(srna, "use_snap_current_frame_to_strips", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "snap_flag", SEQ_SNAP_CURRENT_FRAME_TO_STRIPS);
+  RNA_def_property_ui_text(
+      prop, "Snap Current Frame to Strips", "Snap current frame to strip start or end");
+
   prop = RNA_def_property(srna, "snap_distance", PROP_INT, PROP_PIXEL);
   RNA_def_property_int_sdna(prop, NULL, "snap_distance");
   RNA_def_property_int_default(prop, 15);