From c5dff902a6a6ffcb851763ba740ff3d138d8f2bb Mon Sep 17 00:00:00 2001
From: Falk David <falk@blender.org>
Date: Fri, 19 Jan 2024 14:58:00 +0100
Subject: [PATCH] GPV3: Modifiers: Add `get_drawing_infos_for_write`

This API returns a vector with a pointer to each drawing as well
as the starting frame for the keyframe that the drawing came from.
---
 .../intern/MOD_grease_pencil_util.cc          | 30 +++++++++++++++++--
 .../intern/MOD_grease_pencil_util.hh          | 10 +++++++
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/source/blender/modifiers/intern/MOD_grease_pencil_util.cc b/source/blender/modifiers/intern/MOD_grease_pencil_util.cc
index a348a172180..6d32cec0c99 100644
--- a/source/blender/modifiers/intern/MOD_grease_pencil_util.cc
+++ b/source/blender/modifiers/intern/MOD_grease_pencil_util.cc
@@ -37,6 +37,7 @@
 namespace blender::modifier::greasepencil {
 
 using bke::greasepencil::Drawing;
+using bke::greasepencil::FramesMapKey;
 using bke::greasepencil::Layer;
 
 void init_influence_data(GreasePencilModifierInfluenceData *influence_data,
@@ -310,12 +311,12 @@ IndexMask get_filtered_stroke_mask(const Object *ob,
 
 Vector<bke::greasepencil::Drawing *> get_drawings_for_write(GreasePencil &grease_pencil,
                                                             const IndexMask &layer_mask,
-                                                            int frame)
+                                                            const int frame)
 {
   /* Set of unique drawing indices. */
   Set<int> drawing_indices;
   for (const int64_t i : layer_mask.index_range()) {
-    Layer *layer = grease_pencil.layers_for_write()[layer_mask[i]];
+    const Layer *layer = grease_pencil.layers()[layer_mask[i]];
     const int drawing_index = layer->drawing_index_at(frame);
     if (drawing_index >= 0) {
       drawing_indices.add(drawing_index);
@@ -334,4 +335,29 @@ Vector<bke::greasepencil::Drawing *> get_drawings_for_write(GreasePencil &grease
   return drawings;
 }
 
+Vector<DrawingInfo> get_drawing_infos_for_write(GreasePencil &grease_pencil,
+                                                const IndexMask &layer_mask,
+                                                const int frame)
+{
+  Set<int> drawing_indices;
+  Vector<DrawingInfo> drawing_infos;
+  for (const int64_t i : layer_mask.index_range()) {
+    const Layer *layer = grease_pencil.layers()[layer_mask[i]];
+    const std::optional<FramesMapKey> start_frame = layer->frame_key_at(frame);
+    if (!start_frame) {
+      continue;
+    }
+    const GreasePencilFrame &frame = layer->frames().lookup(*start_frame);
+    if (!drawing_indices.contains(frame.drawing_index)) {
+      drawing_indices.add(frame.drawing_index);
+      GreasePencilDrawingBase *drawing_base = grease_pencil.drawing(frame.drawing_index);
+      if (drawing_base->type == GP_DRAWING) {
+        GreasePencilDrawing *drawing = reinterpret_cast<GreasePencilDrawing *>(drawing_base);
+        drawing_infos.append({&drawing->wrap(), *start_frame});
+      }
+    }
+  }
+  return drawing_infos;
+}
+
 }  // namespace blender::modifier::greasepencil
diff --git a/source/blender/modifiers/intern/MOD_grease_pencil_util.hh b/source/blender/modifiers/intern/MOD_grease_pencil_util.hh
index 9652ff47e0d..d0a70ab316c 100644
--- a/source/blender/modifiers/intern/MOD_grease_pencil_util.hh
+++ b/source/blender/modifiers/intern/MOD_grease_pencil_util.hh
@@ -63,4 +63,14 @@ Vector<bke::greasepencil::Drawing *> get_drawings_for_write(GreasePencil &grease
                                                             const IndexMask &layer_mask,
                                                             int frame);
 
+struct DrawingInfo {
+  bke::greasepencil::Drawing *drawing;
+  /* Frame on which this drawing starts. */
+  int start_frame_number;
+};
+
+Vector<DrawingInfo> get_drawing_infos_for_write(GreasePencil &grease_pencil,
+                                                const IndexMask &layer_mask,
+                                                int frame);
+
 }  // namespace blender::modifier::greasepencil