From ba3e17e990d9631a32e2423506d94a2c75111c7a Mon Sep 17 00:00:00 2001
From: Amelie Fondevilla <amelie.fondevilla@les-fees-speciales.coop>
Date: Fri, 25 Aug 2023 10:28:44 +0200
Subject: [PATCH 1/2] Add ED function to snap frame numbers in grease pencil

---
 .../intern/grease_pencil_frames.cc            | 47 +++++++++++++++++++
 .../editors/include/ED_grease_pencil.hh       |  5 ++
 2 files changed, 52 insertions(+)

diff --git a/source/blender/editors/grease_pencil/intern/grease_pencil_frames.cc b/source/blender/editors/grease_pencil/intern/grease_pencil_frames.cc
index 04017d7ab3f..fa2d6889b6c 100644
--- a/source/blender/editors/grease_pencil/intern/grease_pencil_frames.cc
+++ b/source/blender/editors/grease_pencil/intern/grease_pencil_frames.cc
@@ -19,6 +19,7 @@
 
 #include "ED_grease_pencil.hh"
 #include "ED_keyframes_edit.hh"
+#include "ED_markers.hh"
 
 #include "RNA_access.hh"
 #include "RNA_define.hh"
@@ -27,6 +28,52 @@
 
 namespace blender::ed::greasepencil {
 
+static float get_snapped_frame_number(const float frame_number,
+                                      Scene &scene,
+                                      const eEditKeyframes_Snap mode)
+{
+  switch (mode) {
+    case SNAP_KEYS_CURFRAME: /* Snap to current frame. */
+      return scene.r.cfra;
+    case SNAP_KEYS_NEARSEC: /* Snap to nearest second. */
+    {
+      float secf = (scene.r.frs_sec / scene.r.frs_sec_base);
+      return floorf(frame_number / secf + 0.5f) * secf;
+    }
+    case SNAP_KEYS_NEARMARKER: /* Snap to nearest marker. */
+      return ED_markers_find_nearest_marker_time(&scene.markers, frame_number);
+    default:
+      break;
+  }
+  return frame_number;
+}
+
+bool snap_layer_frames(GreasePencil &grease_pencil,
+                       bke::greasepencil::Layer &layer,
+                       Scene &scene,
+                       const eEditKeyframes_Snap mode)
+{
+  bool changed = false;
+  blender::Map<int, int> frame_number_destinations;
+  for (auto [frame_number, frame] : layer.frames().items()) {
+    if (!frame.is_selected()) {
+      continue;
+    }
+    const int snapped = round_fl_to_int(
+        get_snapped_frame_number(float(frame_number), scene, mode));
+    if (snapped != frame_number) {
+      frame_number_destinations.add(frame_number, snapped);
+      changed = true;
+    }
+  }
+
+  if (changed) {
+    grease_pencil.move_frames(layer, frame_number_destinations);
+  }
+
+  return changed;
+}
+
 bool remove_all_selected_frames(GreasePencil &grease_pencil, bke::greasepencil::Layer &layer)
 {
   Vector<int> frames_to_remove;
diff --git a/source/blender/editors/include/ED_grease_pencil.hh b/source/blender/editors/include/ED_grease_pencil.hh
index 656c03e3bc7..21f20de1ea6 100644
--- a/source/blender/editors/include/ED_grease_pencil.hh
+++ b/source/blender/editors/include/ED_grease_pencil.hh
@@ -47,6 +47,11 @@ eAttrDomain ED_grease_pencil_selection_domain_get(bContext *C);
 
 namespace blender::ed::greasepencil {
 
+bool snap_layer_frames(GreasePencil &grease_pencil,
+                       bke::greasepencil::Layer &layer,
+                       Scene &scene,
+                       const eEditKeyframes_Snap mode);
+
 bool remove_all_selected_frames(GreasePencil &grease_pencil, bke::greasepencil::Layer &layer);
 
 void select_layer_channel(GreasePencil &grease_pencil, bke::greasepencil::Layer *layer);
-- 
2.30.2


From 56d90e7430b0a60d12480dafa84e5e27f8456703 Mon Sep 17 00:00:00 2001
From: Amelie Fondevilla <amelie.fondevilla@les-fees-speciales.coop>
Date: Fri, 25 Aug 2023 10:28:55 +0200
Subject: [PATCH 2/2] Implementation of the snap operator

---
 source/blender/editors/space_action/action_edit.cc | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/source/blender/editors/space_action/action_edit.cc b/source/blender/editors/space_action/action_edit.cc
index f24e2ca8f41..c9921f18f96 100644
--- a/source/blender/editors/space_action/action_edit.cc
+++ b/source/blender/editors/space_action/action_edit.cc
@@ -1898,7 +1898,15 @@ static void snap_action_keys(bAnimContext *ac, short mode)
       ED_gpencil_layer_snap_frames(static_cast<bGPDlayer *>(ale->data), ac->scene, mode);
     }
     else if (ale->type == ANIMTYPE_GREASE_PENCIL_LAYER) {
-      /* GPv3: To be implemented. */
+      GreasePencil *grease_pencil = reinterpret_cast<GreasePencil *>(ale->id);
+      GreasePencilLayer *layer = static_cast<GreasePencilLayer *>(ale->data);
+
+      const bool changed = blender::ed::greasepencil::snap_layer_frames(
+          *grease_pencil, layer->wrap(), *(ac->scene), static_cast<eEditKeyframes_Snap>(mode));
+
+      if (changed) {
+        DEG_id_tag_update(&grease_pencil->id, ID_RECALC_GEOMETRY);
+      }
     }
     else if (ale->type == ANIMTYPE_MASKLAYER) {
       ED_masklayer_snap_frames(static_cast<MaskLayer *>(ale->data), ac->scene, mode);
-- 
2.30.2