Animation: Add GP layers in regular Dopesheet

Grease Pencil animation channels are now also shown in the Dopesheet
mode of the Dopesheet editor and in the Timeline.

Grease pencil related events are now listened not only by container
`SACTCONT_GPENCIL` (Grease Pencil Dopesheet), but also
`SACTCONT_DOPESHEET` (main Dopesheet), and `SACTCONT_TIMELINE`
(timeline).

A new Animation Filter flag was added: `ANIMFILTER_FCURVESONLY`. For now
this only filters out Grease Pencil Layer channels.

**Implemented:**

- Preview range set: now only considers selected Grease Pencil keyframes
  when `onlySel` parameter is true. Not only this allows the operator to
  work with grease pencil keyframes in main dopesheet, but it also fixes
  the operator in the Grease Pencil dopesheet.
- Translation: allocation (and freeing) of specific memory for
  translation of Grease Pencil keyframes.
- Copy/Paste: call to both Fcurve and GPencil operators, to allow for
  mixed selection. Errors are only reported when both the FCurve and
  GPencil functions fail to paste anything.
- Keyframe Type change and Insert Keyframe: removed some code here to
  unify Grease Pencil dopesheet and main dopesheet code.

- Jump, Snap, Mirror, Select all/box/lasso/circle, Select left/right,
  Clickselect: account for Grease Pencil channels within the channels
  loop, no need for `ANIMFILTER_FCURVESONLY` there.

**Not Implemented:**

- Graph-related operators. The filter `ANIMFILTER_FCURVESONLY` is
  naively added to all graph-related operators, meaning more-or-less all
  operators that used `ANIMFILTER_CURVE_VISIBLE`.
- Select linked: is for F-curves channel only
- Select more/less: not yet implemented for grease pencil layers.
- Clean Keys, Sample, Extrapolation, Interpolation, Easing, and Handle
  type change: work on Fcurve-channels only, so the
  `ANIMFILTER_FCURVESONLY` filter is activated

Graying out these operators (when no fcurve keyframe is selected) can be
done with custom poll functions BUT may affect performance. This is NOT
done in this patch.

**Dopesheet Summary Selection:**

The main summary of the dopesheet now also takes into account Grease
Pencil keyframes, using some nasty copy/pasting of code, as explained
[on devtalk](https://devtalk.blender.org/t/gpencil-layers-integration-in-main-dopesheet-selection-issue/24527).
It works, but may be improved, providing some deeper changes.

Reviewed By: mendio, pepeland, sybren

Maniphest Tasks: T97477

Differential Revision: https://developer.blender.org/D15003

3 files changed, 24 insertions, 5 deletions

diff --git a/source/blender/editors/include/ED_anim_api.h b/source/blender/editors/include/ED_anim_api.h
index da40eef87fd..ac3b4133007 100644
--- a/source/blender/editors/include/ED_anim_api.h
+++ b/source/blender/editors/include/ED_anim_api.h
@@ -324,11 +324,15 @@ typedef enum eAnimFilter_Flags {
   /** duplicate entries for animation data attached to multi-user blocks must not occur */
   ANIMFILTER_NODUPLIS = (1 << 11),
 
+  /** avoid channel that does not have any F-curve data */
+  ANIMFILTER_FCURVESONLY = (1 << 12),
+
   /** for checking if we should keep some collapsed channel around (internal use only!) */
   ANIMFILTER_TMP_PEEK = (1 << 30),
 
   /** Ignore ONLYSEL flag from #bDopeSheet.filterflag (internal use only!) */
   ANIMFILTER_TMP_IGNORE_ONLYSEL = (1u << 31),
+
 } eAnimFilter_Flags;
 
 /** \} */
diff --git a/source/blender/editors/include/ED_gpencil.h b/source/blender/editors/include/ED_gpencil.h
index d844bd59c9d..b6488d6da56 100644
--- a/source/blender/editors/include/ED_gpencil.h
+++ b/source/blender/editors/include/ED_gpencil.h
@@ -281,6 +281,11 @@ void ED_gpencil_select_frames(struct bGPDlayer *gpl, short select_mode);
 void ED_gpencil_select_frame(struct bGPDlayer *gpl, int selx, short select_mode);
 
 /**
+ * Set the layer's channel as active
+ */
+void ED_gpencil_set_active_channel(struct bGPdata *gpd, struct bGPDlayer *gpl);
+
+/**
  * Delete selected frames.
  */
 bool ED_gpencil_layer_frames_delete(struct bGPDlayer *gpl);
diff --git a/source/blender/editors/include/ED_keyframes_edit.h b/source/blender/editors/include/ED_keyframes_edit.h
index 163797d395d..9596c3a7fed 100644
--- a/source/blender/editors/include/ED_keyframes_edit.h
+++ b/source/blender/editors/include/ED_keyframes_edit.h
@@ -229,6 +229,16 @@ typedef enum eKeyMergeMode {
   KEYFRAME_PASTE_MERGE_OVER_RANGE_ALL,
 } eKeyMergeMode;
 
+/* Possible errors occurring while pasting keys. */
+typedef enum eKeyPasteError {
+  /* No errors occurred */
+  KEYFRAME_PASTE_OK,
+  /* Nothing was copied */
+  KEYFRAME_PASTE_NOTHING_TO_PASTE,
+  /* No F-curves was selected to paste into*/
+  KEYFRAME_PASTE_NOWHERE_TO_PASTE
+} eKeyPasteError;
+
 /** \} */
 
 /* -------------------------------------------------------------------- */
@@ -416,11 +426,11 @@ void sample_fcurve(struct FCurve *fcu);
 
 void ANIM_fcurves_copybuf_free(void);
 short copy_animedit_keys(struct bAnimContext *ac, ListBase *anim_data);
-short paste_animedit_keys(struct bAnimContext *ac,
-                          ListBase *anim_data,
-                          eKeyPasteOffset offset_mode,
-                          eKeyMergeMode merge_mode,
-                          bool flip);
+eKeyPasteError paste_animedit_keys(struct bAnimContext *ac,
+                                   ListBase *anim_data,
+                                   eKeyPasteOffset offset_mode,
+                                   eKeyMergeMode merge_mode,
+                                   bool flip);
 
 /* ************************************************ */