GPencil: Improve Thickness handling for Outline operator

Actually, when you increase the thickness of the stroke in the outline conversion, the shape of the stroke changes and becomes thicker.

This commit includes a new algorithm to correct this problem. A new `Keep Shape`  parameter allows you to disable it because, for artist reasons, it may be good to keep the old algorithm and change the shape.

1 files changed, 6 insertions, 2 deletions

diff --git a/source/blender/blenkernel/intern/gpencil_geom.cc b/source/blender/blenkernel/intern/gpencil_geom.cc
index d0075a7d161..f7d84b8dc84 100644
--- a/source/blender/blenkernel/intern/gpencil_geom.cc
+++ b/source/blender/blenkernel/intern/gpencil_geom.cc
@@ -3960,6 +3960,7 @@ static ListBase *gpencil_stroke_perimeter_ex(const bGPdata *gpd,
                                              const bGPDlayer *gpl,
                                              const bGPDstroke *gps,
                                              int subdivisions,
+                                             const float thickness_chg,
                                              int *r_num_perimeter_points)
 {
   /* sanity check */
@@ -3968,7 +3969,9 @@ static ListBase *gpencil_stroke_perimeter_ex(const bGPdata *gpd,
   }
 
   float defaultpixsize = 1000.0f / gpd->pixfactor;
+  float ovr_radius = thickness_chg / defaultpixsize / 2.0f;
   float stroke_radius = ((gps->thickness + gpl->line_change) / defaultpixsize) / 2.0f;
+  stroke_radius = max_ff(stroke_radius - ovr_radius, 0.0f);
 
   ListBase *perimeter_right_side = MEM_cnew<ListBase>(__func__);
   ListBase *perimeter_left_side = MEM_cnew<ListBase>(__func__);
@@ -4202,7 +4205,8 @@ bGPDstroke *BKE_gpencil_stroke_perimeter_from_view(struct RegionView3D *rv3d,
                                                    const bGPDlayer *gpl,
                                                    bGPDstroke *gps,
                                                    const int subdivisions,
-                                                   const float diff_mat[4][4])
+                                                   const float diff_mat[4][4],
+                                                   const float thickness_chg)
 {
   if (gps->totpoints == 0) {
     return nullptr;
@@ -4234,7 +4238,7 @@ bGPDstroke *BKE_gpencil_stroke_perimeter_from_view(struct RegionView3D *rv3d,
   BKE_gpencil_stroke_to_view_space(rv3d, gps_temp, diff_mat);
   int num_perimeter_points = 0;
   ListBase *perimeter_points = gpencil_stroke_perimeter_ex(
-      gpd, gpl, gps_temp, subdivisions, &num_perimeter_points);
+      gpd, gpl, gps_temp, subdivisions, thickness_chg, &num_perimeter_points);
 
   if (num_perimeter_points == 0) {
     return nullptr;