source/blender/blenkernel/BKE_grease_pencil.cpp

@@ -0,0 +1,6 @@
+#include "BKE_grease_pencil.hh"
+
+Span<GreasePencilDrawing> blender::bke::GreasePencil::drawings() const
+{
+  return Span<GreasePencilDrawing>{this->drawing_array, this->drawing_array_size};
+}

source/blender/blenkernel/BKE_grease_pencil.hh

@@ -0,0 +1,57 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#pragma once
+
+/** \file
+ * \ingroup bke
+ * \brief Low-level operations for grease pencil.
+ */
+
+#include "BLI_map.hh"
+#include "DNA_grease_pencil_types.h"
+
+namespace blender::bke {
+
+class GreasePencilLayerRuntime {
+ private:
+  Map<int, int> frames;
+};
+
+// class GreasePencilLayer : ::GreasePencilLayer {
+//  public:
+//   GreasePencilLayer();
+//   GreasePencilLayer(const GreasePencilLayer &other);
+//   GreasePencilLayer(GreasePencilLayer &&other);
+//   GreasePencilLayer &operator=(const GreasePencilLayer &other);
+//   GreasePencilLayer &operator=(GreasePencilLayer &&other);
+//   ~GreasePencilLayer();
+
+//   /* --------------------------------------------------------------------
+//    * Accessors.
+//    */
+
+//   int frames_num() const;
+// };
+
+class GreasePencil : ::GreasePencil {
+ public:
+  GreasePencil() = delete;
+  GreasePencil(const GreasePencil &other);
+  GreasePencil(GreasePencil &&other);
+  GreasePencil &operator=(const GreasePencil &other);
+  GreasePencil &operator=(GreasePencil &&other);
+  ~GreasePencil();
+
+  /* --------------------------------------------------------------------
+   * Accessors.
+   */
+
+  Span<GreasePencilDrawing> drawings() const;
+};
+
+}  // namespace blender::bke
+
+inline blender::Map<int, int> GreasePencilLayer::frames() const
+{
+  return this->runtime->frames;
+}

source/blender/blenkernel/BKE_main.h

@@ -200,6 +200,7 @@ typedef struct Main {
   ListBase pointclouds;
   ListBase volumes;
   ListBase simulations;
+  ListBase greasepencils;
 
   /**
    * Must be generated, used and freed by same code - never assume this is valid data unless you

source/blender/blenkernel/CMakeLists.txt

@@ -148,6 +148,7 @@ set(SRC
   intern/gpencil_geom_legacy.cc
   intern/gpencil_modifier_legacy.c
   intern/gpencil_update_cache_legacy.c
+  intern/grease_pencil.cc
   intern/icons.cc
   intern/icons_rasterize.c
   intern/idprop.c

source/blender/blenkernel/intern/grease_pencil.cc

@@ -0,0 +1,102 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+/** \file
+ * \ingroup bke
+ */
+
+#include "BKE_grease_pencil.hh"
+#include "BKE_idtype.h"
+#include "BKE_lib_query.h"
+
+#include "BLO_read_write.h"
+
+#include "BLT_translation.h"
+
+#include "DNA_ID.h"
+#include "DNA_ID_enums.h"
+#include "DNA_grease_pencil_types.h"
+
+#include "MEM_guardedalloc.h"
+
+static void grease_pencil_init_data(ID *id)
+{
+}
+
+static void grease_pencil_copy_data(Main * /*bmain*/, ID *id_dst, const ID *id_src, const int flag)
+{
+}
+
+static void grease_pencil_free_data(ID *id)
+{
+  GreasePencil *grease_pencil = (GreasePencil *)id;
+  BKE_animdata_free(&grease_pencil->id, false);
+
+  // TODO: free drawing array
+  // TODO: free layer tree
+
+  MEM_SAFE_FREE(grease_pencil->mat);
+}
+
+static void grease_pencil_foreach_id(ID *id, LibraryForeachIDData *data)
+{
+  GreasePencil *grease_pencil = (GreasePencil *)id;
+  for (int i = 0; i < grease_pencil->mat_num; i++) {
+    BKE_LIB_FOREACHID_PROCESS_IDSUPER(data, grease_pencil->mat[i], IDWALK_CB_USER);
+  }
+  // TODO: walk all the referenced drawings
+}
+
+static void grease_pencil_blend_write(BlendWriter *writer, ID *id, const void *id_address)
+{
+}
+
+static void grease_pencil_blend_read_data(BlendDataReader *reader, ID *id)
+{
+}
+
+static void grease_pencil_blend_read_lib(BlendLibReader *reader, ID *id)
+{
+}
+
+static void grease_pencil_blend_read_expand(BlendExpander *expander, ID *id)
+{
+  GreasePencil *grease_pencil = (GreasePencil *)id;
+  for (int i = 0; i < grease_pencil->mat_num; i++) {
+    BLO_expand(expander, grease_pencil->mat[i]);
+  }
+}
+
+IDTypeInfo IDType_ID_GP = {
+    /*id_code*/ ID_GP,
+    /*id_filter*/ FILTER_ID_GP,
+    /*main_listbase_index*/ INDEX_ID_GP,
+    /*struct_size*/ sizeof(GreasePencil),
+    /*name*/ "GreasePencil",
+    /*name_plural*/ "grease_pencils_new",
+    /*translation_context*/ BLT_I18NCONTEXT_ID_GPENCIL,
+    /*flags*/ IDTYPE_FLAGS_APPEND_IS_REUSABLE,
+    /*asset_type_info*/ nullptr,
+
+    /*init_data*/ grease_pencil_init_data,
+    /*copy_data*/ grease_pencil_copy_data,
+    /*free_data*/ grease_pencil_free_data,
+    /*make_local*/ nullptr,
+    /*foreach_id*/ grease_pencil_foreach_id,
+    /*foreach_cache*/ nullptr,
+    /*foreach_path*/ nullptr,
+    /*owner_pointer_get*/ nullptr,
+
+    /*blend_write*/ grease_pencil_blend_write,
+    /*blend_read_data*/ grease_pencil_blend_read_data,
+    /*blend_read_lib*/ grease_pencil_blend_read_lib,
+    /*blend_read_expand*/ grease_pencil_blend_read_expand,
+
+    /*blend_read_undo_preserve*/ nullptr,
+
+    /*lib_override_apply_post*/ nullptr,
+};
+
+Span<GreasePencilDrawing> blender::bke::GreasePencil::drawings() const
+{
+  return Span<GreasePencilDrawing>{this->drawing_array, this->drawing_array_size};
+}

source/blender/blenkernel/intern/main.c

@@ -714,6 +714,7 @@ int set_listbasepointers(Main *bmain, ListBase *lb[/*INDEX_ID_MAX*/])
   lb[INDEX_ID_WM] = &(bmain->wm);
   lb[INDEX_ID_MSK] = &(bmain->masks);
   lb[INDEX_ID_SIM] = &(bmain->simulations);
+  lb[INDEX_ID_GP] = &(bmain->greasepencils);
 
   lb[INDEX_ID_NULL] = NULL;
 

source/blender/blenloader/intern/readfile.cc

@@ -2985,6 +2985,8 @@ static const char *dataname(short id_code)
       return "Data from VO";
     case ID_SIM:
       return "Data from SIM";
+    case ID_GP:
+      return "Data from GP";
   }
   return "Data from Lib Block";
 }

source/blender/depsgraph/intern/builder/deg_builder_nodes.cc

@@ -608,6 +608,7 @@ void DepsgraphNodeBuilder::build_id(ID *id)
     case ID_CV:
     case ID_PT:
     case ID_VO:
+    case ID_GP:
       build_object_data_geometry_datablock(id);
       break;
     case ID_SPK:

source/blender/depsgraph/intern/builder/deg_builder_relations.cc

@@ -549,6 +549,7 @@ void DepsgraphRelationBuilder::build_id(ID *id)
     case ID_PT:
     case ID_VO:
     case ID_GD_LEGACY:
+    case ID_GP:
       build_object_data_geometry_datablock(id);
       break;
     case ID_SPK:

source/blender/editors/interface/interface_icons.cc

@@ -2436,6 +2436,8 @@ int UI_icon_from_idcode(const int idcode)
     case ID_SIM:
       /* TODO: Use correct icon. */
       return ICON_PHYSICS;
+    case ID_GP:
+      return ICON_OUTLINER_DATA_GREASEPENCIL;
 
     /* No icons for these ID-types. */
     case ID_LI:

source/blender/makesdna/DNA_ID.h

@@ -1097,6 +1097,7 @@ typedef enum IDRecalcFlag {
 #define FILTER_ID_SCR (1ULL << 37)
 #define FILTER_ID_WM (1ULL << 38)
 #define FILTER_ID_LI (1ULL << 39)
+#define FILTER_ID_GP (1ULL << 40)
 
 #define FILTER_ID_ALL \
   (FILTER_ID_AC | FILTER_ID_AR | FILTER_ID_BR | FILTER_ID_CA | FILTER_ID_CU_LEGACY | \
@@ -1105,7 +1106,7 @@ typedef enum IDRecalcFlag {
    FILTER_ID_NT | FILTER_ID_OB | FILTER_ID_PA | FILTER_ID_PAL | FILTER_ID_PC | FILTER_ID_SCE | \
    FILTER_ID_SPK | FILTER_ID_SO | FILTER_ID_TE | FILTER_ID_TXT | FILTER_ID_VF | FILTER_ID_WO | \
    FILTER_ID_CF | FILTER_ID_WS | FILTER_ID_LP | FILTER_ID_CV | FILTER_ID_PT | FILTER_ID_VO | \
-   FILTER_ID_SIM | FILTER_ID_KE | FILTER_ID_SCR | FILTER_ID_WM | FILTER_ID_LI)
+   FILTER_ID_SIM | FILTER_ID_KE | FILTER_ID_SCR | FILTER_ID_WM | FILTER_ID_LI | FILTER_ID_GP)
 
 /**
  * This enum defines the index assigned to each type of IDs in the array returned by
@@ -1196,6 +1197,7 @@ enum {
   INDEX_ID_CA,
   INDEX_ID_SPK,
   INDEX_ID_LP,
+  INDEX_ID_GP,
 
   /* Collection and object types. */
   INDEX_ID_OB,

source/blender/makesdna/DNA_ID_enums.h

@@ -82,6 +82,7 @@ typedef enum ID_Type {
   ID_PT = MAKE_ID2('P', 'T'),        /* PointCloud */
   ID_VO = MAKE_ID2('V', 'O'),        /* Volume */
   ID_SIM = MAKE_ID2('S', 'I'),       /* Simulation (geometry node groups) */
+  ID_GP = MAKE_ID2('G', 'P'),        /* Grease Pencil */
 } ID_Type;
 
 /* Only used as 'placeholder' in .blend files for directly linked data-blocks. */

source/blender/makesdna/DNA_grease_pencil_types.h

@@ -0,0 +1,221 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+/** \file
+ * \ingroup DNA
+ */
+
+#pragma once
+
+#include "DNA_ID.h"
+#include "DNA_curves_types.h"
+
+#ifdef __cplusplus
+#  include "BLI_map.hh"
+namespace blender::bke {
+class GreasePencilLayerRuntime;
+}  // namespace blender::bke
+using GreasePencilLayerRuntimeHandle = blender::bke::GreasePencilLayerRuntime;
+#else
+typedef struct GreasePencilLayerRuntimeHandle GreasePencilLayerRuntimeHandle;
+#endif
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct GreasePencil;
+
+typedef enum GreasePencilDrawingType {
+  GREASE_PENCIL_DRAWING = 0,
+  GREASE_PENCIL_DRAWING_REFERENCE = 1,
+} GreasePencilLayerType;
+
+typedef struct GreasePencilDrawingOrReference {
+  char type;
+  /**
+   * Flag. Used to set e.g. the selection status.
+   */
+  int flag;
+} GreasePencilDrawingOrReference;
+
+/**
+ * A grease pencil drawing is a set of strokes. The data is stored using
+ * the CurvesGeometry data structure and the custom attributes within it.
+ * It can either own the data or reference it from another GreasePencil
+ * data-block.
+ *
+ * Note: When a drawing references another data-block, it will always
+ *       reference all the drawings in that data-block sequentially.
+ */
+typedef struct GreasePencilDrawing {
+  GreasePencilDrawingOrReference base;
+  /**
+   * The stroke data for this drawing. Is nullptr in case the drawing
+   * references its data from another data-block.
+   */
+  CurvesGeometry geometry;
+} GreasePencilDrawing;
+
+typedef struct GreasePencilDrawingReference {
+  GreasePencilDrawingOrReference base;
+  /**
+   * A reference to another GreasePencil data-block. Is nullptr in
+   * case the drawing owns its data.
+   *
+   * If the data-block has multiple drawings, this drawing references
+   * all of them sequentially.
+   */
+  struct GreasePencil *id_reference;
+} GreasePencilDrawingReference;
+
+/**
+ * Properties for layers and layer groups.
+ */
+typedef struct GreasePencilLayerProperties {
+  /**
+   * Name of the layer/group. Dynamic length.
+   */
+  char *name;
+
+  /**
+   * Flag. Used to set e.g. the selection, visibility, ... status.
+   */
+  int flag;
+
+  /**
+   * Color tag.
+   */
+  uchar color[3];
+} GreasePencilLayerProperties;
+
+typedef enum GreasePencilLayerTreeElemType {
+  GREASE_PENCIL_LAYER_TREE_LEAF = 0,
+  GREASE_PENCIL_LAYER_TREE_GROUP = 1,
+} GreasePencilLayerType;
+
+typedef struct GreasePencilLayerTreeElem {
+  /**
+   *
+   */
+  char type;
+  struct GreasePencilLayerGroup *parent;
+} GreasePencilLayerTreeElem;
+
+/**
+ * A grease pencil layer is a collection of drawings. It maps them
+ * to specific scene times on the timeline.
+ *
+ * A layer can be a group if it has a non-negative `children_num`.
+ * Layer groups do not have a frames map.
+ *
+ */
+typedef struct GreasePencilLayer {
+  /**
+   * Properties of this layer or group.
+   */
+  GreasePencilLayerProperties properties;
+
+  /**
+   * This Map maps a scene frame number (key) to an index into
+   * GreasePencil->drawings (value). The frame number indicates
+   * the first frame the drawing is shown. The end time is implicitly
+   * defined by the next greater frame number (key) in the map.
+   * If the value mapped to (index) is -1, no drawing is shown
+   * at this frame.
+   *
+   *    Example:
+   *
+   *    {0: 0, 5: 1, 10: -1, 12: 2, 16: -1}
+   *
+   *    In this example there are three drawings (drawing #0,
+   *    drawing #1 and drawing #2). The first drawing starts at frame 0
+   *    and ends at frame 5 (excusive). The second drawing starts at
+   *    frame 5 and ends at frame 10. Finally, the third drawing starts
+   *    at frame 12 and ends at frame 16.
+   *
+   *           | | | | | | | | | | |1|1|1|1|1|1|1|
+   *    Time:  |0|1|2|3|4|5|6|7|8|9|0|1|2|3|4|5|6|...
+   *    Frame: [#0      ][#1      ]    [#2    ]
+   *
+   * Note: If a drawing references another data-block, all of the drawings
+   *       in that data-block are mapped sequentially to the frames.
+   *       If another frame starts, the rest of the mapped drawings
+   *       are discarded.
+   */
+#ifdef __cplusplus
+  const blender::Map<int, int> &frames() const;
+#endif
+
+  /* Only used for storage in the .blend file. */
+  struct {
+    /* Array of `frames` keys. */
+    int *keys;
+    int keys_num;
+
+    /* Array of `frames` values. */
+    int *values;
+    int values_num;
+  } frames_storage;
+
+  /**
+   * Runtime struct pointer.
+   */
+  GreasePencilLayerRuntimeHandle *runtime;
+} GreasePencilLayer;
+
+typedef struct GreasePencilLayerGroup {
+  GreasePencilLayerTreeElem base;
+  /**
+   * Pointer to the parent layer group and to zero or more children elements.
+   */
+  struct GreasePencilLayerTreeElem **children;
+  int children_num;
+} GreasePencilLayerGroup;
+
+typedef struct GreasePencilLayerLeaf {
+  GreasePencilLayerTreeElem base;
+  GreasePencilLayer layer;
+} GreasePencilLayerLeaf;
+
+/**
+ * The grease pencil data-block.
+ * It holds a set of grease pencil drawings, a tree of layer groups, and a set of layers whithin
+ * each layer group.
+ */
+typedef struct GreasePencil {
+  ID id;
+  /** Animation data (must be immediately after #id). */
+  struct AnimData *adt;
+
+  /**
+   * An array of GreasePencilDrawing's.
+   */
+  GreasePencilDrawingOrReference *drawing_array;
+  int drawing_array_size;
+
+  /**
+   * The root layer group (is not shown in the UI).
+   * Its parent is always nullptr.
+   */
+  GreasePencilLayerGroup *root_group;
+
+  /**
+   * An array of materials.
+   */
+  struct Material **material_array;
+  int material_array_size;
+
+  /**
+   * Global flag on the data-block.
+   */
+  int flag;
+
+#ifdef __cplusplus
+  Span<GreasePencilDrawingOrReference> drawings() const;
+#endif
+} GreasePencil;
+
+#ifdef __cplusplus
+}
+#endif