Fix T53832: Particle weight paint crash

Drawing hair weights read before the hair array start.
This code could be improved since it currently copy-pastes,
from do_particle_interpolation, but this would need larger changes.

For now just correct existing logic.

1 files changed, 18 insertions, 10 deletions

diff --git a/source/blender/blenkernel/intern/particle.c b/source/blender/blenkernel/intern/particle.c
index 7a0e8a3578c..455ca3ebbb6 100644
--- a/source/blender/blenkernel/intern/particle.c
+++ b/source/blender/blenkernel/intern/particle.c
@@ -2827,7 +2827,8 @@ void psys_cache_edit_paths(Scene *scene, Object *ob, PTCacheEdit *edit, float cf
 		if (pset->brushtype == PE_BRUSH_WEIGHT) {
 			pind.hkey[0] = NULL;
 			/* pa != NULL since the weight brush is only available for hair */
-			pind.hkey[1] = pa->hair;
+			pind.hkey[0] = pa->hair;
+			pind.hkey[1] = pa->hair + 1;
 		}
 
 
@@ -2885,12 +2886,26 @@ void psys_cache_edit_paths(Scene *scene, Object *ob, PTCacheEdit *edit, float cf
 
 			/* selection coloring in edit mode */
 			if (pset->brushtype == PE_BRUSH_WEIGHT) {
-				float t2;
-
 				if (k == 0) {
 					weight_to_rgb(ca->col, pind.hkey[1]->weight);
 				}
 				else {
+					/* warning: copied from 'do_particle_interpolation' (without 'mvert' array stepping) */
+					float real_t;
+					if (result.time < 0.0f) {
+						real_t = -result.time;
+					}
+					else {
+						real_t = pind.hkey[0]->time + t * (pind.hkey[0][pa->totkey - 1].time - pind.hkey[0]->time);
+					}
+
+					while (pind.hkey[1]->time < real_t) {
+						pind.hkey[1]++;
+					}
+					pind.hkey[0] = pind.hkey[1] - 1;
+					/* end copy */
+
+
 					float w1[3], w2[3];
 					keytime = (t - (*pind.ekey[0]->time)) / ((*pind.ekey[1]->time) - (*pind.ekey[0]->time));
 
@@ -2899,13 +2914,6 @@ void psys_cache_edit_paths(Scene *scene, Object *ob, PTCacheEdit *edit, float cf
 
 					interp_v3_v3v3(ca->col, w1, w2, keytime);
 				}
-
-				/* at the moment this is only used for weight painting.
-				 * will need to move out of this check if its used elsewhere. */
-				t2 = birthtime + ((float)k / (float)segments) * (dietime - birthtime);
-
-				while (pind.hkey[1]->time < t2) pind.hkey[1]++;
-				pind.hkey[0] = pind.hkey[1] - 1;
 			}
 			else {
 				if ((ekey + (pind.ekey[0] - point->keys))->flag & PEK_SELECT) {