GPencil: Fill tool refactor and Multiframe in Draw mode

This commit is a refactor of the fill tool to solve several problems we had since the first version of the tool.

Changes:

* The filling speed has been improved for each step of the process with the optimization of each algorithm/function.
* New `AutoFit` option to fill areas outside of the viewport. When enable, the total size of the frame is calculated to fit the filling area.
* New support multiframe filling. Now it is possible to fill multiple similar frames in one go.
* New `Stroke Extension` option to create temporary closing strokes. These strokes can be displayed and adjusted dynamically using wheel mouse or PageUp/Down keys.
* Parameter `Resolution` now is named `Precision` and has been moved to topbar.
* `Resolution` now has decimals and can be lower than 1 to allow quick filling in storyboarding workflows. Maximum value has been set as 5.
* Parameter `Simplify` has been moved to Advanced panel.
* Improved fill outline detection. In some cases, the outline penetrated the area to be filled with unexpected results.
* Fixes some corner case bugs with infinite loops.

As a result of this refactor, also these new functionalities has been added.

* New support for multiframe in `Draw` mode. Any drawing in active frame is duplicated to all selected frame.
* New multiframe display mode. Keyframes before or after of the active frame are displayed using onion colors. This can be disable using Onion overlay options.

1 files changed, 6 insertions, 0 deletions

diff --git a/source/blender/editors/gpencil/gpencil_primitive.c b/source/blender/editors/gpencil/gpencil_primitive.c
index d94a02204a2..bcdde49b93d 100644
--- a/source/blender/editors/gpencil/gpencil_primitive.c
+++ b/source/blender/editors/gpencil/gpencil_primitive.c
@@ -1377,6 +1377,12 @@ static void gpencil_primitive_interaction_end(bContext *C,
     BKE_gpencil_stroke_geometry_update(tgpi->gpd, gps);
   }
 
+  /* In Multiframe mode, duplicate the stroke in other frames. */
+  if (GPENCIL_MULTIEDIT_SESSIONS_ON(tgpi->gpd)) {
+    const bool tail = (ts->gpencil_flags & GP_TOOL_FLAG_PAINT_ONBACK);
+    BKE_gpencil_stroke_copy_to_keyframes(tgpi->gpd, tgpi->gpl, gpf, gps, tail);
+  }
+
   DEG_id_tag_update(&tgpi->gpd->id, ID_RECALC_COPY_ON_WRITE);
   DEG_id_tag_update(&tgpi->gpd->id, ID_RECALC_TRANSFORM | ID_RECALC_GEOMETRY);