GPencil: Smooth thickness when joining strokes

When joining two strokes in paint mode using the auto merge option, the join was very hard if the thickness was too different.

This patch adds a smooth to the join in order to get better transition.

Also fixed the problem to join existing strokes very far from actual stroke.

Some cleanup and rename of old code is included in order to make code more readable.

Reviewed By: pepeland

Differential Revision: https://developer.blender.org/D12362

1 files changed, 26 insertions, 1 deletions

diff --git a/source/blender/editors/gpencil/gpencil_utils.c b/source/blender/editors/gpencil/gpencil_utils.c
index 5cc52303cd6..72d10d840fa 100644
--- a/source/blender/editors/gpencil/gpencil_utils.c
+++ b/source/blender/editors/gpencil/gpencil_utils.c
@@ -3213,11 +3213,28 @@ bool ED_gpencil_stroke_point_is_inside(const bGPDstroke *gps,
   return hit;
 }
 
+/* Get extremes of stroke in 2D using current view. */
+void ED_gpencil_stroke_extremes_to2d(const GP_SpaceConversion *gsc,
+                                     const float diff_mat[4][4],
+                                     bGPDstroke *gps,
+                                     float r_ctrl1[2],
+                                     float r_ctrl2[2])
+{
+  bGPDspoint pt_dummy_ps;
+
+  gpencil_point_to_parent_space(&gps->points[0], diff_mat, &pt_dummy_ps);
+  gpencil_point_to_xy_fl(gsc, gps, &pt_dummy_ps, &r_ctrl1[0], &r_ctrl1[1]);
+  gpencil_point_to_parent_space(&gps->points[gps->totpoints - 1], diff_mat, &pt_dummy_ps);
+  gpencil_point_to_xy_fl(gsc, gps, &pt_dummy_ps, &r_ctrl2[0], &r_ctrl2[1]);
+}
+
 bGPDstroke *ED_gpencil_stroke_nearest_to_ends(bContext *C,
                                               const GP_SpaceConversion *gsc,
                                               bGPDlayer *gpl,
                                               bGPDframe *gpf,
                                               bGPDstroke *gps,
+                                              const float ctrl1[2],
+                                              const float ctrl2[2],
                                               const float radius,
                                               int *r_index)
 {
@@ -3267,6 +3284,14 @@ bGPDstroke *ED_gpencil_stroke_nearest_to_ends(bContext *C,
     gpencil_point_to_parent_space(pt, diff_mat, &pt_parent);
     gpencil_point_to_xy_fl(gsc, gps, &pt_parent, &pt2d_target_end[0], &pt2d_target_end[1]);
 
+    /* If the distance to the original stroke extremes is too big, the stroke must not be joined. */
+    if ((len_squared_v2v2(ctrl1, pt2d_target_start) > radius_sqr) &&
+        (len_squared_v2v2(ctrl1, pt2d_target_end) > radius_sqr) &&
+        (len_squared_v2v2(ctrl2, pt2d_target_start) > radius_sqr) &&
+        (len_squared_v2v2(ctrl2, pt2d_target_end) > radius_sqr)) {
+      continue;
+    }
+
     if ((len_squared_v2v2(pt2d_start, pt2d_target_start) > radius_sqr) &&
         (len_squared_v2v2(pt2d_start, pt2d_target_end) > radius_sqr) &&
         (len_squared_v2v2(pt2d_end, pt2d_target_start) > radius_sqr) &&
@@ -3350,7 +3375,7 @@ bGPDstroke *ED_gpencil_stroke_join_and_trim(
 
   /* Join both strokes. */
   int totpoint = gps_final->totpoints;
-  BKE_gpencil_stroke_join(gps_final, gps, false, true);
+  BKE_gpencil_stroke_join(gps_final, gps, false, true, true);
 
   /* Select the join points and merge if the distance is very small. */
   pt = &gps_final->points[totpoint - 1];