GPencil: Add more types of stroke extensions when filling

The motivation for this change: while working on an animation recently, I found that there are some gaps that won't close easily via stroke extension or leak size checking. In D14698, I attempted to address this by changing the algorithm of the raster-space flood fill. This patch attempts to address the same issue in vector space by adding two new cases where stroke extensions are added, as suggested by @frogstomp:

  # **Points of high curvature:** when the curvature at a point is high enough that it's hard to visually distinguish between it and an endpoint, add a stroke extension out along the normal (pointing in the opposite direction of the stroke's acceleration.) This addresses cases where technically the endpoint points up, but there's a sharp corner right below it that should extend to connect.

  # **Stroke endpoints within a radius**: when two endpoints are close together, regardless of the angle they make, connect them if they are within a radius. This addresses cases like where the two endpoints have effectively parallel tangents, so extensions won't close the gap.

Reviewed By: antoniov, mendio, frogstomp

Differential Revision: https://developer.blender.org/D14809

3 files changed, 13 insertions, 2 deletions

diff --git a/source/blender/makesdna/DNA_brush_enums.h b/source/blender/makesdna/DNA_brush_enums.h
index 988853e6694..0762d304313 100644
--- a/source/blender/makesdna/DNA_brush_enums.h
+++ b/source/blender/makesdna/DNA_brush_enums.h
@@ -118,13 +118,20 @@ typedef enum eGPDbrush_Flag2 {
   GP_BRUSH_USE_UV_RAND_PRESS = (1 << 11),
 } eGPDbrush_Flag2;
 
-/* BrushGpencilSettings->gp_fill_draw_mode */
+/* BrushGpencilSettings->fill_draw_mode */
 typedef enum eGP_FillDrawModes {
   GP_FILL_DMODE_BOTH = 0,
   GP_FILL_DMODE_STROKE = 1,
   GP_FILL_DMODE_CONTROL = 2,
 } eGP_FillDrawModes;
 
+/* BrushGpencilSettings->fill_extend_mode */
+typedef enum eGP_FillExtendModes {
+  GP_FILL_EMODE_LINES_AND_CIRCLES = 0,
+  GP_FILL_EMODE_LINES = 1,
+  GP_FILL_EMODE_CIRCLES = 2,
+} eGP_FillExtendModes;
+
 /* BrushGpencilSettings->fill_layer_mode */
 typedef enum eGP_FillLayerModes {
   GP_FILL_GPLMODE_VISIBLE = 0,
diff --git a/source/blender/makesdna/DNA_brush_types.h b/source/blender/makesdna/DNA_brush_types.h
index 33f5d8eea12..f91321c253f 100644
--- a/source/blender/makesdna/DNA_brush_types.h
+++ b/source/blender/makesdna/DNA_brush_types.h
@@ -62,7 +62,7 @@ typedef struct BrushGpencilSettings {
   short fill_leak;
   /* Type of caps: eGPDstroke_Caps. */
   int8_t caps_type;
-  char _pad;
+  char _pad[5];
 
   int flag2;
 
@@ -70,6 +70,8 @@ typedef struct BrushGpencilSettings {
   int fill_simplylvl;
   /** Type of control lines drawing mode. */
   int fill_draw_mode;
+  /** Type of gap filling to use */
+  int fill_extend_mode;
   /** Icon identifier. */
   int icon_id;
 
diff --git a/source/blender/makesdna/DNA_gpencil_types.h b/source/blender/makesdna/DNA_gpencil_types.h
index 6a2f25f3975..17b25021277 100644
--- a/source/blender/makesdna/DNA_gpencil_types.h
+++ b/source/blender/makesdna/DNA_gpencil_types.h
@@ -347,6 +347,8 @@ typedef enum eGPDstroke_Flag {
   /* Flag to indicated that the editcurve has been changed and the stroke needs to be updated with
    * the curve data */
   GP_STROKE_NEEDS_CURVE_UPDATE = (1 << 9),
+  /* Flag to indicate that a stroke is used only for help, and will not affect rendering or fill */
+  GP_STROKE_HELP = (1 << 10),
   /* only for use with stroke-buffer (while drawing arrows) */
   GP_STROKE_USE_ARROW_START = (1 << 12),
   /* only for use with stroke-buffer (while drawing arrows) */