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, 39 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/gpencil_geom.c b/source/blender/blenkernel/intern/gpencil_geom.c
index 60ffa3c3e73..2ef85439a46 100644
--- a/source/blender/blenkernel/intern/gpencil_geom.c
+++ b/source/blender/blenkernel/intern/gpencil_geom.c
@@ -3228,6 +3228,45 @@ void BKE_gpencil_stroke_join(bGPDstroke *gps_a,
   }
 }
 
+/* Copy the stroke of the frame to all frames selected (except current). */
+void BKE_gpencil_stroke_copy_to_keyframes(
+    bGPdata *gpd, bGPDlayer *gpl, bGPDframe *gpf, bGPDstroke *gps, const bool tail)
+{
+  GHash *frame_list = BLI_ghash_int_new_ex(__func__, 64);
+  BKE_gpencil_frame_selected_hash(gpd, frame_list);
+
+  GHashIterator gh_iter;
+  GHASH_ITER (gh_iter, frame_list) {
+    int cfra = POINTER_AS_INT(BLI_ghashIterator_getKey(&gh_iter));
+
+    if (gpf->framenum != cfra) {
+      bGPDframe *gpf_new = BKE_gpencil_layer_frame_find(gpl, cfra);
+      if (gpf_new == NULL) {
+        gpf_new = BKE_gpencil_frame_addnew(gpl, cfra);
+      }
+
+      if (gpf_new == NULL) {
+        continue;
+      }
+
+      bGPDstroke *gps_new = BKE_gpencil_stroke_duplicate(gps, true, true);
+      if (gps_new == NULL) {
+        continue;
+      }
+
+      if (tail) {
+        BLI_addhead(&gpf_new->strokes, gps_new);
+      }
+      else {
+        BLI_addtail(&gpf_new->strokes, gps_new);
+      }
+    }
+  }
+
+  /* Free hash table. */
+  BLI_ghash_free(frame_list, NULL, NULL);
+}
+
 /* Stroke Uniform Subdivide  ------------------------------------- */
 
 typedef struct tSamplePoint {