GPencil: New BKE function to set stroke start point

This function allows to set the start point for cyclic strokes.

The function is required by a new modifier and operator
that are currently under development.

4 files changed, 74 insertions, 42 deletions

diff --git a/source/blender/blenkernel/BKE_gpencil_geom.h b/source/blender/blenkernel/BKE_gpencil_geom.h
index 33735fddf55..88244ec9d64 100644
--- a/source/blender/blenkernel/BKE_gpencil_geom.h
+++ b/source/blender/blenkernel/BKE_gpencil_geom.h
@@ -406,7 +406,13 @@ void BKE_gpencil_stroke_join(struct bGPDstroke *gps_a,
                              struct bGPDstroke *gps_b,
                              bool leave_gaps,
                              bool fit_thickness,
-                             bool smooth);
+                             bool smooth,
+                             bool auto_flip);
+/**
+ * Set stroke start point in the selected index. Only works for Cyclic strokes.
+ * \param start_idx: Index of the point to be the start point.
+ */
+void BKE_gpencil_stroke_start_set(struct bGPdata *gpd, struct bGPDstroke *gps, int start_idx);
 /**
  * Copy the stroke of the frame to all frames selected (except current).
  */
diff --git a/source/blender/blenkernel/intern/gpencil_geom.cc b/source/blender/blenkernel/intern/gpencil_geom.cc
index 2f1049999d2..2cc752dca47 100644
--- a/source/blender/blenkernel/intern/gpencil_geom.cc
+++ b/source/blender/blenkernel/intern/gpencil_geom.cc
@@ -3415,7 +3415,8 @@ void BKE_gpencil_stroke_join(bGPDstroke *gps_a,
                              bGPDstroke *gps_b,
                              const bool leave_gaps,
                              const bool fit_thickness,
-                             const bool smooth)
+                             const bool smooth,
+                             bool auto_flip)
 {
   bGPDspoint point;
   bGPDspoint *pt;
@@ -3432,52 +3433,54 @@ void BKE_gpencil_stroke_join(bGPDstroke *gps_a,
     return;
   }
 
-  /* define start and end points of each stroke */
-  float start_a[3], start_b[3], end_a[3], end_b[3];
-  pt = &gps_a->points[0];
-  copy_v3_v3(start_a, &pt->x);
+  if (auto_flip) {
+    /* define start and end points of each stroke */
+    float start_a[3], start_b[3], end_a[3], end_b[3];
+    pt = &gps_a->points[0];
+    copy_v3_v3(start_a, &pt->x);
 
-  pt = &gps_a->points[gps_a->totpoints - 1];
-  copy_v3_v3(end_a, &pt->x);
+    pt = &gps_a->points[gps_a->totpoints - 1];
+    copy_v3_v3(end_a, &pt->x);
 
-  pt = &gps_b->points[0];
-  copy_v3_v3(start_b, &pt->x);
+    pt = &gps_b->points[0];
+    copy_v3_v3(start_b, &pt->x);
 
-  pt = &gps_b->points[gps_b->totpoints - 1];
-  copy_v3_v3(end_b, &pt->x);
+    pt = &gps_b->points[gps_b->totpoints - 1];
+    copy_v3_v3(end_b, &pt->x);
 
-  /* Check if need flip strokes. */
-  float dist = len_squared_v3v3(end_a, start_b);
-  bool flip_a = false;
-  bool flip_b = false;
-  float lowest = dist;
+    /* Check if need flip strokes. */
+    float dist = len_squared_v3v3(end_a, start_b);
+    bool flip_a = false;
+    bool flip_b = false;
+    float lowest = dist;
 
-  dist = len_squared_v3v3(end_a, end_b);
-  if (dist < lowest) {
-    lowest = dist;
-    flip_a = false;
-    flip_b = true;
-  }
+    dist = len_squared_v3v3(end_a, end_b);
+    if (dist < lowest) {
+      lowest = dist;
+      flip_a = false;
+      flip_b = true;
+    }
 
-  dist = len_squared_v3v3(start_a, start_b);
-  if (dist < lowest) {
-    lowest = dist;
-    flip_a = true;
-    flip_b = false;
-  }
+    dist = len_squared_v3v3(start_a, start_b);
+    if (dist < lowest) {
+      lowest = dist;
+      flip_a = true;
+      flip_b = false;
+    }
 
-  dist = len_squared_v3v3(start_a, end_b);
-  if (dist < lowest) {
-    lowest = dist;
-    flip_a = true;
-    flip_b = true;
-  }
+    dist = len_squared_v3v3(start_a, end_b);
+    if (dist < lowest) {
+      lowest = dist;
+      flip_a = true;
+      flip_b = true;
+    }
 
-  if (flip_a) {
-    BKE_gpencil_stroke_flip(gps_a);
-  }
-  if (flip_b) {
-    BKE_gpencil_stroke_flip(gps_b);
+    if (flip_a) {
+      BKE_gpencil_stroke_flip(gps_a);
+    }
+    if (flip_b) {
+      BKE_gpencil_stroke_flip(gps_b);
+    }
   }
 
   /* don't visibly link the first and last points? */
@@ -3540,6 +3543,29 @@ void BKE_gpencil_stroke_join(bGPDstroke *gps_a,
   }
 }
 
+void BKE_gpencil_stroke_start_set(bGPdata *gpd, bGPDstroke *gps, int start_idx)
+{
+  if ((start_idx < 1) || (start_idx >= gps->totpoints)) {
+    return;
+  }
+
+  /* Only cyclic strokes. */
+  if ((gps->flag & GP_STROKE_CYCLIC) == 0) {
+    return;
+  }
+
+  bGPDstroke *gps_b = BKE_gpencil_stroke_duplicate(gps, true, false);
+  BKE_gpencil_stroke_trim_points(gps_b, 0, start_idx - 0);
+  BKE_gpencil_stroke_trim_points(gps, start_idx, gps->totpoints - 1);
+
+  /* Join both strokes. */
+  BKE_gpencil_stroke_join(gps, gps_b, false, false, false, false);
+
+  BKE_gpencil_stroke_geometry_update(gpd, gps);
+
+  BKE_gpencil_free_stroke(gps_b);
+}
+
 void BKE_gpencil_stroke_copy_to_keyframes(
     bGPdata *gpd, bGPDlayer *gpl, bGPDframe *gpf, bGPDstroke *gps, const bool tail)
 {
diff --git a/source/blender/editors/gpencil/gpencil_edit.c b/source/blender/editors/gpencil/gpencil_edit.c
index b826f033cc0..106f4acd6b7 100644
--- a/source/blender/editors/gpencil/gpencil_edit.c
+++ b/source/blender/editors/gpencil/gpencil_edit.c
@@ -3650,7 +3650,7 @@ 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, false);
+    BKE_gpencil_stroke_join(gps_new, elem->gps, leave_gaps, true, false, true);
     elem->used = true;
   }
 
diff --git a/source/blender/editors/gpencil/gpencil_utils.c b/source/blender/editors/gpencil/gpencil_utils.c
index 7b659511aaa..c905404061c 100644
--- a/source/blender/editors/gpencil/gpencil_utils.c
+++ b/source/blender/editors/gpencil/gpencil_utils.c
@@ -3189,7 +3189,7 @@ bGPDstroke *ED_gpencil_stroke_join_and_trim(
 
   /* Join both strokes. */
   int totpoint = gps_final->totpoints;
-  BKE_gpencil_stroke_join(gps_final, gps, false, true, true);
+  BKE_gpencil_stroke_join(gps_final, gps, false, true, true, true);
 
   /* Select the join points and merge if the distance is very small. */
   pt = &gps_final->points[totpoint - 1];