source/blender/makesdna/DNA_modifier_types.h

@@ -152,8 +152,8 @@ typedef enum {
    */
   eModifierFlag_Active = (1 << 2),
   /**
-   * Only set on modifiers in evaluated objects. The flag indicates that the user modified inputs
-   * to the modifier which might invalidate simulation caches.
+   * Only set on modifiers in evaluated objects. The flag indicates that the user modified
+   * inputs to the modifier which might invalidate simulation caches.
    */
   eModifierFlag_UserModified = (1 << 3),
 } ModifierFlag;

source/blender/modifiers/CMakeLists.txt

@@ -45,6 +45,7 @@ set(SRC
   intern/MOD_explode.cc
   intern/MOD_fluid.cc
   intern/MOD_grease_pencil_opacity.cc
+  intern/MOD_grease_pencil_util.cc
   intern/MOD_hook.cc
   intern/MOD_laplaciandeform.cc
   intern/MOD_laplaciansmooth.cc
@@ -98,6 +99,7 @@ set(SRC
 
   MOD_modifiertypes.hh
   MOD_nodes.hh
+  intern/MOD_grease_pencil_util.hh
   intern/MOD_meshcache_util.hh
   intern/MOD_solidify_util.hh
   intern/MOD_ui_common.hh

source/blender/modifiers/intern/MOD_grease_pencil_opacity.cc

@@ -10,11 +10,17 @@
 
 #include "DNA_defaults.h"
 #include "DNA_modifier_types.h"
+#include "DNA_scene_types.h"
 
+#include "BKE_curves.hh"
+#include "BKE_geometry_set.hh"
+#include "BKE_grease_pencil.hh"
 #include "BKE_modifier.hh"
 
 #include "BLO_read_write.hh"
 
+#include "DEG_depsgraph_query.hh"
+
 #include "UI_interface.hh"
 #include "UI_resources.hh"
 
@@ -26,11 +32,16 @@
 #include "RNA_enum_types.hh"
 #include "RNA_prototypes.h"
 
+#include "MOD_grease_pencil_util.hh"
 #include "MOD_modifiertypes.hh"
 #include "MOD_ui_common.hh"
 
 namespace blender {
 
+using bke::greasepencil::Drawing;
+using bke::greasepencil::FramesMapKey;
+using bke::greasepencil::Layer;
+
 static void init_data(ModifierData *md)
 {
   GreasePencilOpacityModifierData *omd = (GreasePencilOpacityModifierData *)md;
@@ -69,14 +80,43 @@ static void free_data(ModifierData *md)
   UNUSED_VARS(omd);
 }
 
+static void modify_curves(ModifierData *md,
+                          const ModifierEvalContext * /*ctx*/,
+                          bke::CurvesGeometry &curves)
+{
+  GreasePencilOpacityModifierData *omd = (GreasePencilOpacityModifierData *)md;
+  UNUSED_VARS(omd);
+
+  bke::MutableAttributeAccessor attributes = curves.attributes_for_write();
+  bke::SpanAttributeWriter<float> opacities = attributes.lookup_or_add_for_write_span<float>(
+      "opacity", bke::AttrDomain::Point);
+
+  for (const int i : opacities.span.index_range()) {
+    opacities.span[i] *= 0.5f;
+  }
+
+  opacities.finish();
+}
+
 static void modify_geometry_set(ModifierData *md,
                                 const ModifierEvalContext *ctx,
                                 bke::GeometrySet *geometry_set)
 {
-  GreasePencilOpacityModifierData *omd = (GreasePencilOpacityModifierData *)md;
+  const Scene *scene = DEG_get_evaluated_scene(ctx->depsgraph);
+  const int frame = scene->r.cfra;
 
-  // TODO
-  UNUSED_VARS(omd, ctx, geometry_set);
+  GreasePencilOpacityModifierData *omd = (GreasePencilOpacityModifierData *)md;
+  UNUSED_VARS(omd);
+
+  GreasePencil *grease_pencil = geometry_set->get_grease_pencil_for_write();
+  if (grease_pencil == nullptr) {
+    return;
+  }
+
+  Vector<Drawing *> drawings = greasepencil::get_drawings_for_write(*grease_pencil, frame);
+  for (Drawing *drawing : drawings) {
+    modify_curves(md, ctx, drawing->strokes_for_write());
+  }
 }
 
 static void panel_draw(const bContext * /*C*/, Panel *panel)
@@ -119,7 +159,7 @@ ModifierTypeInfo modifierType_GreasePencilOpacity = {
     /*struct_name*/ "GreasePencilOpacityModifierData",
     /*struct_size*/ sizeof(GreasePencilOpacityModifierData),
     /*srna*/ &RNA_GreasePencilOpacityModifier,
-    /*type*/ ModifierTypeType::NonGeometrical,
+    /*type*/ ModifierTypeType::Nonconstructive,
     /*flags*/
     static_cast<ModifierTypeFlag>(
         eModifierTypeFlag_AcceptsGreasePencil | eModifierTypeFlag_SupportsEditmode |

source/blender/modifiers/intern/MOD_grease_pencil_util.cc

@@ -0,0 +1,45 @@
+/* SPDX-FileCopyrightText: 2011 by Bastien Montagne. All rights reserved.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later */
+
+/** \file
+ * \ingroup modifiers
+ */
+
+#include "MOD_grease_pencil_util.hh"
+
+#include "BLI_set.hh"
+
+#include "DNA_grease_pencil_types.h"
+
+#include "BKE_grease_pencil.hh"
+
+namespace blender::greasepencil {
+
+using bke::greasepencil::Drawing;
+using bke::greasepencil::Layer;
+
+Vector<bke::greasepencil::Drawing *> get_drawings_for_write(GreasePencil &grease_pencil, int frame)
+{
+  /* Set of unique drawing indices. */
+  Set<int> drawing_indices;
+  for (Layer *layer : grease_pencil.layers_for_write()) {
+    const int drawing_index = layer->drawing_index_at(frame);
+    if (drawing_index >= 0) {
+      drawing_indices.add(drawing_index);
+    }
+  }
+
+  /* List of owned drawings, ignore drawing references to other data blocks. */
+  Vector<bke::greasepencil::Drawing *> drawings;
+  for (const int drawing_index : drawing_indices) {
+    GreasePencilDrawingBase *drawing_base = grease_pencil.drawing(drawing_index);
+    if (drawing_base->type == GP_DRAWING) {
+      GreasePencilDrawing *drawing = reinterpret_cast<GreasePencilDrawing *>(drawing_base);
+      drawings.append(&drawing->wrap());
+    }
+  }
+  return drawings;
+}
+
+}  // namespace blender::greasepencil

source/blender/modifiers/intern/MOD_grease_pencil_util.hh

@@ -0,0 +1,23 @@
+/* SPDX-FileCopyrightText: 2011 by Bastien Montagne. All rights reserved.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later */
+
+/** \file
+ * \ingroup modifiers
+ */
+
+#pragma once
+
+#include "BLI_vector.hh"
+
+struct GreasePencil;
+namespace blender::bke::greasepencil {
+class Drawing;
+}
+
+namespace blender::greasepencil {
+
+Vector<bke::greasepencil::Drawing *> get_drawings_for_write(GreasePencil &grease_pencil,
+                                                            int frame);
+
+}