From 59f9a5e6ac6f5bff914204ef299cba27bb5016eb Mon Sep 17 00:00:00 2001
From: Robert Sheldon <rsheldiii>
Date: Thu, 15 Jul 2021 15:58:34 +0200
Subject: Fix T88188: Allow keyframing vertex mass in cloth sim

Update vertex weights between simulation steps if they have changed.
This allows for animated vertex weights in the cloth sim.

Reviewed By: Sebastian Parborg

Differential Revision: http://developer.blender.org/D11640
---
 source/blender/blenkernel/intern/cloth.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

(limited to 'source/blender/blenkernel/intern/cloth.c')

diff --git a/source/blender/blenkernel/intern/cloth.c b/source/blender/blenkernel/intern/cloth.c
index 8678a659c0a..0fa58a74f2b 100644
--- a/source/blender/blenkernel/intern/cloth.c
+++ b/source/blender/blenkernel/intern/cloth.c
@@ -262,17 +262,19 @@ static bool do_init_cloth(Object *ob, ClothModifierData *clmd, Mesh *result, int
 static int do_step_cloth(
     Depsgraph *depsgraph, Object *ob, ClothModifierData *clmd, Mesh *result, int framenr)
 {
+  /* simulate 1 frame forward */
   ClothVertex *verts = NULL;
   Cloth *cloth;
   ListBase *effectors = NULL;
   MVert *mvert;
   unsigned int i = 0;
   int ret = 0;
+  bool vert_mass_changed = false;
 
-  /* simulate 1 frame forward */
   cloth = clmd->clothObject;
   verts = cloth->verts;
   mvert = result->mvert;
+  vert_mass_changed = verts->mass != clmd->sim_parms->mass;
 
   /* force any pinned verts to their constrained location. */
   for (i = 0; i < clmd->clothObject->mvert_num; i++, verts++) {
@@ -283,6 +285,11 @@ static int do_step_cloth(
     /* Get the current position. */
     copy_v3_v3(verts->xconst, mvert[i].co);
     mul_m4_v3(ob->obmat, verts->xconst);
+
+    if (vert_mass_changed) {
+      verts->mass = clmd->sim_parms->mass;
+      SIM_mass_spring_set_implicit_vertex_mass(cloth->implicit, i, verts->mass);
+    }
   }
 
   effectors = BKE_effectors_create(depsgraph, ob, NULL, clmd->sim_parms->effector_weights, false);
-- 
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