GP: Draw: Stroke Trim

New edit mode operator and post-processing brush option.

Trim works on a single GP stroke. It removes trailing points before and after the first intersection (or loop) nearest to the start of the stroke.

2 files changed, 96 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_gpencil.h b/source/blender/blenkernel/BKE_gpencil.h
index a33f172b961..eb4101fa2f7 100644
--- a/source/blender/blenkernel/BKE_gpencil.h
+++ b/source/blender/blenkernel/BKE_gpencil.h
@@ -160,6 +160,7 @@ void BKE_gpencil_stroke_normal(const struct bGPDstroke *gps, float r_normal[3]);
 void BKE_gpencil_simplify_stroke(struct bGPDstroke *gps, float factor);
 void BKE_gpencil_simplify_fixed(struct bGPDstroke *gps);
 void BKE_gpencil_subdivide(struct bGPDstroke *gps, int level, int flag);
+bool BKE_gpencil_trim_stroke(struct bGPDstroke *gps);
 
 void BKE_gpencil_stroke_2d_flat(
 	const struct bGPDspoint *points, int totpoints, float(*points2d)[2], int *r_direction);
diff --git a/source/blender/blenkernel/intern/gpencil.c b/source/blender/blenkernel/intern/gpencil.c
index ad41382f854..108192c5be9 100644
--- a/source/blender/blenkernel/intern/gpencil.c
+++ b/source/blender/blenkernel/intern/gpencil.c
@@ -1700,3 +1700,98 @@ void BKE_gpencil_stroke_2d_flat_ref(
 	/* Concave (-1), Convex (1), or Autodetect (0)? */
 	*r_direction = (int)locy[2];
 }
+
+/**
+ * Trim stroke to the first intersection or loop
+ * \param gps: Stroke data
+ */
+bool BKE_gpencil_trim_stroke(bGPDstroke *gps)
+{
+	if (gps->totpoints < 4) {
+		return false;
+	}
+	bool intersect = false;
+	int start, end;
+	float point[3];
+	/* loop segments from start until we have an intersection */
+	for (int i = 0; i < gps->totpoints - 2; i++) {
+		start = i;
+		bGPDspoint *a = &gps->points[start];
+		bGPDspoint *b = &gps->points[start + 1];
+		for (int j = start + 2; j < gps->totpoints - 1; j++) {
+			end = j + 1;
+			bGPDspoint *c = &gps->points[j];
+			bGPDspoint *d = &gps->points[end];
+			float pointb[3];
+			/* get intersection */
+			if (isect_line_line_v3(&a->x, &b->x, &c->x, &d->x, point, pointb)) {
+				if (len_v3(point) > 0.0f) {
+					float closest[3];
+					/* check intersection is on both lines */
+					float lambda = closest_to_line_v3(closest, point, &a->x, &b->x);
+					if ((lambda <= 0.0f) || (lambda >= 1.0f)) {
+						continue;
+					}
+					lambda = closest_to_line_v3(closest, point, &c->x, &d->x);
+					if ((lambda <= 0.0f) || (lambda >= 1.0f)) {
+						continue;
+					}
+					else {
+						intersect = true;
+						break;
+					}
+				}
+			}
+		}
+		if (intersect) {
+			break;
+		}
+	}
+
+	/* trim unwanted points */
+	if (intersect) {
+
+		/* save points */
+		bGPDspoint *old_points = MEM_dupallocN(gps->points);
+		MDeformVert *old_dvert = NULL;
+		MDeformVert *dvert_src = NULL;
+
+		if (gps->dvert != NULL) {
+			old_dvert = MEM_dupallocN(gps->dvert);
+		}
+
+		/* resize gps */
+		int newtot = end - start + 1;
+
+		gps->points = MEM_recallocN(gps->points, sizeof(*gps->points) * newtot);
+		if (gps->dvert != NULL) {
+			gps->dvert = MEM_recallocN(gps->dvert, sizeof(*gps->dvert) * newtot);
+		}
+
+		for (int i = 0; i < newtot; i++) {
+			int idx = start + i;
+			bGPDspoint *pt_src = &old_points[idx];
+			bGPDspoint *pt_new = &gps->points[i];
+			memcpy(pt_new, pt_src, sizeof(bGPDspoint));
+			if (gps->dvert != NULL) {
+				dvert_src = &old_dvert[idx];
+				MDeformVert *dvert = &gps->dvert[i];
+				memcpy(dvert, dvert_src, sizeof(MDeformVert));
+				if (dvert_src->dw) {
+					memcpy(dvert->dw, dvert_src->dw, sizeof(MDeformWeight));
+				}
+			}
+			if (idx == start || idx == end) {
+				copy_v3_v3(&pt_new->x, point);
+			}
+		}
+
+		gps->flag |= GP_STROKE_RECALC_GEOMETRY;
+		gps->tot_triangles = 0;
+		gps->totpoints = newtot;
+
+		MEM_SAFE_FREE(old_points);
+		MEM_SAFE_FREE(old_dvert);
+	}
+	return intersect;
+}