[Bf-blender-cvs] [1f16b5d7940] blender-v2.93-release: Fix T94137: GPencil: Eraser does not erase first point

[Philipp Oeser]

Commit: 1f16b5d7940594a09bf0420389e16d4360893d2a
Author: Philipp Oeser
Date:   Thu Dec 16 11:22:23 2021 +0100
Branches: blender-v2.93-release
https://developer.blender.org/rB1f16b5d7940594a09bf0420389e16d4360893d2a

Fix T94137: GPencil: Eraser does not erase first point

The eraser checks the current, previous and next point (and sets pc0,
pc1 & pc2 corresponding to that for futher occlusion/brush/clipping
checks). For the very first point, it sets pc0 to pc1 [which makes sense,
there is no previous point, so we should assume the previous segment is
"visible" as soon as the first point is], but does so *before* pc1 is
even calculated. This makes following occlusion/brush/clipping checks
work with zero values [which leads to no earsing in most cases].

Now *first* calculate pc1, *then* set pc0 to pc1.

Maniphest Tasks: T94137

Differential Revision: https://developer.blender.org/D13593

===================================================================

M	source/blender/editors/gpencil/gpencil_paint.c

===================================================================

diff --git a/source/blender/editors/gpencil/gpencil_paint.c b/source/blender/editors/gpencil/gpencil_paint.c
index 644f02a1c42..1a59eba803d 100644
--- a/source/blender/editors/gpencil/gpencil_paint.c
+++ b/source/blender/editors/gpencil/gpencil_paint.c
@@ -1569,6 +1569,12 @@ static void gpencil_stroke_eraser_dostroke(tGPsdata *p,
       }
 
       bGPDspoint npt;
+      gpencil_point_to_parent_space(pt1, p->diff_mat, &npt);
+      gpencil_point_to_xy(&p->gsc, gps, &npt, &pc1[0], &pc1[1]);
+
+      gpencil_point_to_parent_space(pt2, p->diff_mat, &npt);
+      gpencil_point_to_xy(&p->gsc, gps, &npt, &pc2[0], &pc2[1]);
+
       if (pt0) {
         gpencil_point_to_parent_space(pt0, p->diff_mat, &npt);
         gpencil_point_to_xy(&p->gsc, gps, &npt, &pc0[0], &pc0[1]);
@@ -1578,12 +1584,6 @@ static void gpencil_stroke_eraser_dostroke(tGPsdata *p,
         copy_v2_v2_int(pc0, pc1);
       }
 
-      gpencil_point_to_parent_space(pt1, p->diff_mat, &npt);
-      gpencil_point_to_xy(&p->gsc, gps, &npt, &pc1[0], &pc1[1]);
-
-      gpencil_point_to_parent_space(pt2, p->diff_mat, &npt);
-      gpencil_point_to_xy(&p->gsc, gps, &npt, &pc2[0], &pc2[1]);
-
       /* Check that point segment of the boundbox of the eraser stroke */
       if (((!ELEM(V2D_IS_CLIPPED, pc0[0], pc0[1])) && BLI_rcti_isect_pt(rect, pc0[0], pc0[1])) ||
           ((!ELEM(V2D_IS_CLIPPED, pc1[0], pc1[1])) && BLI_rcti_isect_pt(rect, pc1[0], pc1[1])) ||