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

7 files changed, 62 insertions, 12 deletions

diff --git a/source/blender/editors/gpencil/gpencil_edit.c b/source/blender/editors/gpencil/gpencil_edit.c
index 8d1f841da6c..aa3178ddc2c 100644
--- a/source/blender/editors/gpencil/gpencil_edit.c
+++ b/source/blender/editors/gpencil/gpencil_edit.c
@@ -3618,7 +3618,7 @@ static int gpencil_stroke_join_exec(bContext *C, wmOperator *op)
     }
     elem = &strokes_list[i];
     /* Join new_stroke and stroke B. */
-    BKE_gpencil_stroke_join(gps_new, elem->gps, leave_gaps, true);
+    BKE_gpencil_stroke_join(gps_new, elem->gps, leave_gaps, true, false);
     elem->used = true;
   }
 
@@ -3967,7 +3967,7 @@ static void gpencil_smooth_stroke(bContext *C, wmOperator *op)
 
           /* perform smoothing */
           if (smooth_position) {
-            BKE_gpencil_stroke_smooth(gps, i, factor);
+            BKE_gpencil_stroke_smooth_point(gps, i, factor);
           }
           if (smooth_strength) {
             BKE_gpencil_stroke_smooth_strength(gps, i, factor);
diff --git a/source/blender/editors/gpencil/gpencil_fill.c b/source/blender/editors/gpencil/gpencil_fill.c
index 0c88d678ef4..f5474a7cdc3 100644
--- a/source/blender/editors/gpencil/gpencil_fill.c
+++ b/source/blender/editors/gpencil/gpencil_fill.c
@@ -1569,7 +1569,7 @@ static void gpencil_stroke_from_buffer(tGPDfill *tgpf)
   float smoothfac = 1.0f;
   for (int r = 0; r < 1; r++) {
     for (int i = 0; i < gps->totpoints; i++) {
-      BKE_gpencil_stroke_smooth(gps, i, smoothfac - reduce);
+      BKE_gpencil_stroke_smooth_point(gps, i, smoothfac - reduce);
     }
     reduce += 0.25f; /* reduce the factor */
   }
diff --git a/source/blender/editors/gpencil/gpencil_interpolate.c b/source/blender/editors/gpencil/gpencil_interpolate.c
index a8bd3b11bb1..fdd9f44605e 100644
--- a/source/blender/editors/gpencil/gpencil_interpolate.c
+++ b/source/blender/editors/gpencil/gpencil_interpolate.c
@@ -333,7 +333,7 @@ static void gpencil_interpolate_smooth_stroke(bGPDstroke *gps,
   float reduce = 0.0f;
   for (int r = 0; r < smooth_steps; r++) {
     for (int i = 0; i < gps->totpoints - 1; i++) {
-      BKE_gpencil_stroke_smooth(gps, i, smooth_factor - reduce);
+      BKE_gpencil_stroke_smooth_point(gps, i, smooth_factor - reduce);
       BKE_gpencil_stroke_smooth_strength(gps, i, smooth_factor);
     }
     reduce += 0.25f; /* reduce the factor */
diff --git a/source/blender/editors/gpencil/gpencil_paint.c b/source/blender/editors/gpencil/gpencil_paint.c
index 28a22633742..9b157224178 100644
--- a/source/blender/editors/gpencil/gpencil_paint.c
+++ b/source/blender/editors/gpencil/gpencil_paint.c
@@ -1209,7 +1209,8 @@ static void gpencil_stroke_newfrombuffer(tGPsdata *p)
       float reduce = 0.0f;
       for (int r = 0; r < brush->gpencil_settings->draw_smoothlvl; r++) {
         for (i = 0; i < gps->totpoints - 1; i++) {
-          BKE_gpencil_stroke_smooth(gps, i, brush->gpencil_settings->draw_smoothfac - reduce);
+          BKE_gpencil_stroke_smooth_point(
+              gps, i, brush->gpencil_settings->draw_smoothfac - reduce);
           BKE_gpencil_stroke_smooth_strength(gps, i, brush->gpencil_settings->draw_smoothfac);
         }
         reduce += 0.25f; /* reduce the factor */
@@ -1221,7 +1222,7 @@ static void gpencil_stroke_newfrombuffer(tGPsdata *p)
       float ifac = (float)brush->gpencil_settings->input_samples / 10.0f;
       float sfac = interpf(1.0f, 0.2f, ifac);
       for (i = 0; i < gps->totpoints - 1; i++) {
-        BKE_gpencil_stroke_smooth(gps, i, sfac);
+        BKE_gpencil_stroke_smooth_point(gps, i, sfac);
         BKE_gpencil_stroke_smooth_strength(gps, i, sfac);
       }
     }
@@ -1288,11 +1289,23 @@ static void gpencil_stroke_newfrombuffer(tGPsdata *p)
   /* Join with existing strokes. */
   if (ts->gpencil_flags & GP_TOOL_FLAG_AUTOMERGE_STROKE) {
     if (gps->prev != NULL) {
+      BKE_gpencil_stroke_boundingbox_calc(gps);
+      float diff_mat[4][4], ctrl1[2], ctrl2[2];
+      BKE_gpencil_layer_transform_matrix_get(depsgraph, p->ob, gpl, diff_mat);
+      ED_gpencil_stroke_extremes_to2d(&p->gsc, diff_mat, gps, ctrl1, ctrl2);
+
       int pt_index = 0;
       bool doit = true;
       while (doit && gps) {
-        bGPDstroke *gps_target = ED_gpencil_stroke_nearest_to_ends(
-            p->C, &p->gsc, gpl, gpl->actframe, gps, GPENCIL_MINIMUM_JOIN_DIST, &pt_index);
+        bGPDstroke *gps_target = ED_gpencil_stroke_nearest_to_ends(p->C,
+                                                                   &p->gsc,
+                                                                   gpl,
+                                                                   gpl->actframe,
+                                                                   gps,
+                                                                   ctrl1,
+                                                                   ctrl2,
+                                                                   GPENCIL_MINIMUM_JOIN_DIST,
+                                                                   &pt_index);
         if (gps_target != NULL) {
           gps = ED_gpencil_stroke_join_and_trim(p->gpd, p->gpf, gps, gps_target, pt_index);
         }
diff --git a/source/blender/editors/gpencil/gpencil_primitive.c b/source/blender/editors/gpencil/gpencil_primitive.c
index 5ecb6d9a212..f8cfc130e35 100644
--- a/source/blender/editors/gpencil/gpencil_primitive.c
+++ b/source/blender/editors/gpencil/gpencil_primitive.c
@@ -1382,11 +1382,23 @@ static void gpencil_primitive_interaction_end(bContext *C,
   if (ts->gpencil_flags & GP_TOOL_FLAG_AUTOMERGE_STROKE) {
     if (ELEM(tgpi->type, GP_STROKE_ARC, GP_STROKE_LINE, GP_STROKE_CURVE, GP_STROKE_POLYLINE)) {
       if (gps->prev != NULL) {
+        BKE_gpencil_stroke_boundingbox_calc(gps);
+        float diff_mat[4][4], ctrl1[2], ctrl2[2];
+        BKE_gpencil_layer_transform_matrix_get(tgpi->depsgraph, tgpi->ob, tgpi->gpl, diff_mat);
+        ED_gpencil_stroke_extremes_to2d(&tgpi->gsc, diff_mat, gps, ctrl1, ctrl2);
+
         int pt_index = 0;
         bool doit = true;
         while (doit && gps) {
-          bGPDstroke *gps_target = ED_gpencil_stroke_nearest_to_ends(
-              C, &tgpi->gsc, tgpi->gpl, gpf, gps, GPENCIL_MINIMUM_JOIN_DIST, &pt_index);
+          bGPDstroke *gps_target = ED_gpencil_stroke_nearest_to_ends(C,
+                                                                     &tgpi->gsc,
+                                                                     tgpi->gpl,
+                                                                     gpf,
+                                                                     gps,
+                                                                     ctrl1,
+                                                                     ctrl2,
+                                                                     GPENCIL_MINIMUM_JOIN_DIST,
+                                                                     &pt_index);
           if (gps_target != NULL) {
             gps = ED_gpencil_stroke_join_and_trim(tgpi->gpd, gpf, gps, gps_target, pt_index);
           }
diff --git a/source/blender/editors/gpencil/gpencil_sculpt_paint.c b/source/blender/editors/gpencil/gpencil_sculpt_paint.c
index 869254cef3b..e9a6beab798 100644
--- a/source/blender/editors/gpencil/gpencil_sculpt_paint.c
+++ b/source/blender/editors/gpencil/gpencil_sculpt_paint.c
@@ -337,7 +337,7 @@ static bool gpencil_brush_smooth_apply(tGP_BrushEditData *gso,
 
   /* perform smoothing */
   if (gso->brush->gpencil_settings->sculpt_mode_flag & GP_SCULPT_FLAGMODE_APPLY_POSITION) {
-    BKE_gpencil_stroke_smooth(gps, pt_index, inf);
+    BKE_gpencil_stroke_smooth_point(gps, pt_index, inf);
   }
   if (gso->brush->gpencil_settings->sculpt_mode_flag & GP_SCULPT_FLAGMODE_APPLY_STRENGTH) {
     BKE_gpencil_stroke_smooth_strength(gps, pt_index, inf);
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];