source/blender/blenkernel/intern/grease_pencil.cc

@@ -16,6 +16,7 @@
 
 #include "BLI_math_vector_types.hh"
 #include "BLI_memarena.h"
+#include "BLI_memory_utils.hh"
 #include "BLI_polyfill_2d.h"
 #include "BLI_span.hh"
 #include "BLI_stack.hh"
@@ -440,12 +441,47 @@ blender::Span<blender::bke::StrokePoint> GreasePencilDrawing::stroke_buffer()
 
 /* GreasePencil API */
 
+static void grease_pencil_grow_drawing_array_by(GreasePencil &self, const int added_capacity)
+{
+  BLI_assert(added_capacity > 0);
+  const int new_drawing_array_size = self.drawing_array_size + added_capacity;
+  GreasePencilDrawingOrReference **new_drawing_array =
+      reinterpret_cast<GreasePencilDrawingOrReference **>(
+          MEM_cnew_array<GreasePencilDrawingOrReference *>(new_drawing_array_size, __func__));
+
+  blender::uninitialized_relocate_n(
+      self.drawing_array, self.drawing_array_size, new_drawing_array);
+
+  self.drawing_array = new_drawing_array;
+  self.drawing_array_size = new_drawing_array_size;
+}
+
 blender::Span<GreasePencilDrawingOrReference *> GreasePencil::drawings() const
 {
   return blender::Span<GreasePencilDrawingOrReference *>{this->drawing_array,
                                                          this->drawing_array_size};
 }
 
+blender::MutableSpan<GreasePencilDrawingOrReference *> GreasePencil::drawings_for_write()
+{
+  return blender::MutableSpan<GreasePencilDrawingOrReference *>{this->drawing_array,
+                                                                this->drawing_array_size};
+}
+
+void GreasePencil::add_empty_drawings(int n)
+{
+  using namespace blender;
+  BLI_assert(n > 0);
+  const int prev_size = this->drawings().size();
+  grease_pencil_grow_drawing_array_by(*this, n);
+  MutableSpan<GreasePencilDrawingOrReference *> new_drawings =
+      this->drawings_for_write().drop_front(prev_size);
+  for (const int i : IndexRange(new_drawings.size())) {
+    new_drawings[i] = reinterpret_cast<GreasePencilDrawingOrReference *>(
+        MEM_new<GreasePencilDrawing>(__func__));
+  }
+}
+
 void GreasePencil::foreach_visible_drawing(
     int frame, blender::FunctionRef<void(GreasePencilDrawing &)> function)
 {

source/blender/blenkernel/intern/grease_pencil_test.cc

@@ -33,9 +33,20 @@ TEST(gpencil, create_grease_pencil_id)
 {
   GreasePencilIDTestContext ctx;
 
-  GreasePencil *grease_pencil = static_cast<GreasePencil *>(BKE_id_new(ctx.bmain, ID_GP, "GP"));
-  EXPECT_EQ(grease_pencil->drawings().size(), 0);
-  EXPECT_EQ(grease_pencil->root_group().total_num_children(), 0);
+  GreasePencil &grease_pencil = *static_cast<GreasePencil *>(BKE_id_new(ctx.bmain, ID_GP, "GP"));
+  EXPECT_EQ(grease_pencil.drawings().size(), 0);
+  EXPECT_EQ(grease_pencil.root_group().total_num_children(), 0);
+}
+
+/* --------------------------------------------------------------------------------------------- */
+/* Drawing Array Tests. */
+
+TEST(gpencil, add_empty_drawings)
+{
+  GreasePencilIDTestContext ctx;
+  GreasePencil &grease_pencil = *static_cast<GreasePencil *>(BKE_id_new(ctx.bmain, ID_GP, "GP"));
+  grease_pencil.add_empty_drawings(3);
+  EXPECT_EQ(grease_pencil.drawings().size(), 3);
 }
 
 /* --------------------------------------------------------------------------------------------- */

source/blender/makesdna/DNA_grease_pencil_types.h

@@ -21,7 +21,7 @@ struct StrokePoint;
 namespace gpencil {
 class Layer;
 class LayerGroup;
-}
+}  // namespace gpencil
 }  // namespace blender::bke
 using GreasePencilRuntimeHandle = blender::bke::GreasePencilRuntime;
 using GreasePencilDrawingRuntimeHandle = blender::bke::GreasePencilDrawingRuntime;
@@ -179,6 +179,8 @@ typedef struct GreasePencil {
 
 #ifdef __cplusplus
   blender::Span<GreasePencilDrawingOrReference *> drawings() const;
+  blender::MutableSpan<GreasePencilDrawingOrReference *> drawings_for_write();
+  void add_empty_drawings(int n);
   void foreach_visible_drawing(int frame,
                                blender::FunctionRef<void(GreasePencilDrawing &)> function);
   void read_drawing_array(BlendDataReader *reader);