GPencil: Fill tool refactor and Multiframe in Draw mode

This commit is a refactor of the fill tool to solve several problems we had since the first version of the tool.

Changes:

* The filling speed has been improved for each step of the process with the optimization of each algorithm/function.
* New `AutoFit` option to fill areas outside of the viewport. When enable, the total size of the frame is calculated to fit the filling area.
* New support multiframe filling. Now it is possible to fill multiple similar frames in one go.
* New `Stroke Extension` option to create temporary closing strokes. These strokes can be displayed and adjusted dynamically using wheel mouse or PageUp/Down keys.
* Parameter `Resolution` now is named `Precision` and has been moved to topbar.
* `Resolution` now has decimals and can be lower than 1 to allow quick filling in storyboarding workflows. Maximum value has been set as 5.
* Parameter `Simplify` has been moved to Advanced panel.
* Improved fill outline detection. In some cases, the outline penetrated the area to be filled with unexpected results.
* Fixes some corner case bugs with infinite loops.

As a result of this refactor, also these new functionalities has been added.

* New support for multiframe in `Draw` mode. Any drawing in active frame is duplicated to all selected frame.
* New multiframe display mode. Keyframes before or after of the active frame are displayed using onion colors. This can be disable using Onion overlay options.

1 files changed, 6 insertions, 5 deletions

diff --git a/source/blender/editors/gpencil/drawgpencil.c b/source/blender/editors/gpencil/drawgpencil.c
index 4e2951c3571..751f8333aaa 100644
--- a/source/blender/editors/gpencil/drawgpencil.c
+++ b/source/blender/editors/gpencil/drawgpencil.c
@@ -171,7 +171,8 @@ static void gpencil_draw_stroke_3d(tGPDdraw *tgpw,
   int totpoints = tgpw->gps->totpoints;
 
   const float viewport[2] = {(float)tgpw->winx, (float)tgpw->winy};
-  float curpressure = points[0].pressure;
+  const float min_thickness = 0.05f;
+
   float fpt[3];
 
   /* if cyclic needs more vertex */
@@ -205,7 +206,6 @@ static void gpencil_draw_stroke_3d(tGPDdraw *tgpw,
   immUniform1i("fill_stroke", (int)tgpw->is_fill_stroke);
 
   /* draw stroke curve */
-  GPU_line_width(max_ff(curpressure * thickness, 1.0f));
   immBeginAtMost(GPU_PRIM_LINE_STRIP_ADJ, totpoints + cyclic_add + 2);
   const bGPDspoint *pt = points;
 
@@ -215,18 +215,19 @@ static void gpencil_draw_stroke_3d(tGPDdraw *tgpw,
       gpencil_set_point_varying_color(points, ink, attr_id.color, (bool)tgpw->is_fill_stroke);
 
       if ((cyclic) && (totpoints > 2)) {
-        immAttr1f(attr_id.thickness, max_ff((points + totpoints - 1)->pressure * thickness, 1.0f));
+        immAttr1f(attr_id.thickness,
+                  max_ff((points + totpoints - 1)->pressure * thickness, min_thickness));
         mul_v3_m4v3(fpt, tgpw->diff_mat, &(points + totpoints - 1)->x);
       }
       else {
-        immAttr1f(attr_id.thickness, max_ff((points + 1)->pressure * thickness, 1.0f));
+        immAttr1f(attr_id.thickness, max_ff((points + 1)->pressure * thickness, min_thickness));
         mul_v3_m4v3(fpt, tgpw->diff_mat, &(points + 1)->x);
       }
       immVertex3fv(attr_id.pos, fpt);
     }
     /* set point */
     gpencil_set_point_varying_color(pt, ink, attr_id.color, (bool)tgpw->is_fill_stroke);
-    immAttr1f(attr_id.thickness, max_ff(pt->pressure * thickness, 1.0f));
+    immAttr1f(attr_id.thickness, max_ff(pt->pressure * thickness, min_thickness));
     mul_v3_m4v3(fpt, tgpw->diff_mat, &pt->x);
     immVertex3fv(attr_id.pos, fpt);
   }