Fix T60575: Multiresolution Crashes when appliing more subdivisions

The issue was caused by intermediate DerivedMesh being created with
scene's Simplify settings taken into account. This is what happens
when one area makes implicit decisions based on whether passed Scene
pointer is not NULL.

Made it so ignoring simplification serttings is an explicit flag,
which makes it easier to follow what's going on.

1 files changed, 25 insertions, 12 deletions

diff --git a/source/blender/blenkernel/intern/multires.c b/source/blender/blenkernel/intern/multires.c
index 2e04394fbc8..f0c0046db1f 100644
--- a/source/blender/blenkernel/intern/multires.c
+++ b/source/blender/blenkernel/intern/multires.c
@@ -679,10 +679,12 @@ void multiresModifier_del_levels(MultiresModifierData *mmd, Scene *scene, Object
 	multires_set_tot_level(ob, mmd, lvl);
 }
 
-static DerivedMesh *multires_dm_create_local(Scene *scene, Object *ob, DerivedMesh *dm, int lvl, int totlvl, int simple, bool alloc_paint_mask)
+static DerivedMesh *multires_dm_create_local(
+        Scene *scene, Object *ob, DerivedMesh *dm,
+        int lvl, int totlvl, int simple, bool alloc_paint_mask,
+        int flags)
 {
 	MultiresModifierData mmd = {{NULL}};
-	MultiresFlags flags = MULTIRES_USE_LOCAL_MMD;
 
 	mmd.lvl = lvl;
 	mmd.sculptlvl = lvl;
@@ -690,6 +692,7 @@ static DerivedMesh *multires_dm_create_local(Scene *scene, Object *ob, DerivedMe
 	mmd.totlvl = totlvl;
 	mmd.simple = simple;
 
+	flags |= MULTIRES_USE_LOCAL_MMD;
 	if (alloc_paint_mask)
 		flags |= MULTIRES_ALLOC_PAINT_MASK;
 
@@ -700,10 +703,10 @@ static DerivedMesh *subsurf_dm_create_local(
         Scene *scene, Object *ob, DerivedMesh *dm,
         int lvl,
         bool is_simple, bool is_optimal, bool is_plain_uv, bool alloc_paint_mask,
-        bool for_render)
+        bool for_render,
+        SubsurfFlags flags)
 {
 	SubsurfModifierData smd = {{NULL}};
-	SubsurfFlags flags = 0;
 
 	smd.levels = smd.renderLevels = lvl;
 	smd.quality = 3;
@@ -766,7 +769,7 @@ void multiresModifier_base_apply(MultiresModifierData *mmd, Scene *scene, Object
 	/* generate highest level with displacements */
 	cddm = CDDM_from_mesh(me);
 	DM_set_only_copy(cddm, CD_MASK_BAREMESH);
-	dispdm = multires_dm_create_local(scene, ob, cddm, totlvl, totlvl, 0, 0);
+	dispdm = multires_dm_create_local(scene, ob, cddm, totlvl, totlvl, 0, 0, MULTIRES_IGNORE_SIMPLIFY);
 	cddm->release(cddm);
 
 	/* copy the new locations of the base verts into the mesh */
@@ -862,7 +865,9 @@ void multiresModifier_base_apply(MultiresModifierData *mmd, Scene *scene, Object
 	/* subdivide the mesh to highest level without displacements */
 	cddm = CDDM_from_mesh(me);
 	DM_set_only_copy(cddm, CD_MASK_BAREMESH);
-	origdm = subsurf_dm_create_local(scene, ob, cddm, totlvl, 0, 0, mmd->uv_smooth == SUBSURF_UV_SMOOTH_NONE, 0, false);
+	origdm = subsurf_dm_create_local(
+	        scene, ob, cddm, totlvl, 0, 0, mmd->uv_smooth == SUBSURF_UV_SMOOTH_NONE,
+	        0, false, SUBSURF_IGNORE_SIMPLIFY);
 	cddm->release(cddm);
 
 	/* calc disps */
@@ -903,11 +908,13 @@ static void multires_subdivide(
 		/* create subsurf DM from original mesh at high level */
 		cddm = CDDM_from_mesh(me);
 		DM_set_only_copy(cddm, CD_MASK_BAREMESH);
-		highdm = subsurf_dm_create_local(scene, ob, cddm, totlvl, simple, 0, mmd->uv_smooth == SUBSURF_UV_SMOOTH_NONE, has_mask, false);
+		highdm = subsurf_dm_create_local(
+		        NULL, ob, cddm, totlvl, simple, 0, mmd->uv_smooth == SUBSURF_UV_SMOOTH_NONE,
+		        has_mask, false, SUBSURF_IGNORE_SIMPLIFY);
 		ss = ((CCGDerivedMesh *)highdm)->ss;
 
 		/* create multires DM from original mesh at low level */
-		lowdm = multires_dm_create_local(scene, ob, cddm, lvl, lvl, simple, has_mask);
+		lowdm = multires_dm_create_local(scene, ob, cddm, lvl, lvl, simple, has_mask, MULTIRES_IGNORE_SIMPLIFY);
 		BLI_assert(lowdm != cddm);
 		cddm->release(cddm);
 
@@ -1224,11 +1231,13 @@ void multires_modifier_update_mdisps(struct DerivedMesh *dm, Scene *scene)
 			else cddm = CDDM_from_mesh(me);
 			DM_set_only_copy(cddm, CD_MASK_BAREMESH);
 
-			highdm = subsurf_dm_create_local(scene, ob, cddm, totlvl, mmd->simple, 0, mmd->uv_smooth == SUBSURF_UV_SMOOTH_NONE, has_mask, false);
+			highdm = subsurf_dm_create_local(
+			        scene, ob, cddm, totlvl, mmd->simple, 0, mmd->uv_smooth == SUBSURF_UV_SMOOTH_NONE,
+			        has_mask, false, SUBSURF_IGNORE_SIMPLIFY);
 			ss = ((CCGDerivedMesh *)highdm)->ss;
 
 			/* create multires DM from original mesh and displacements */
-			lowdm = multires_dm_create_local(scene, ob, cddm, lvl, totlvl, mmd->simple, has_mask);
+			lowdm = multires_dm_create_local(scene, ob, cddm, lvl, totlvl, mmd->simple, has_mask, MULTIRES_IGNORE_SIMPLIFY);
 			cddm->release(cddm);
 
 			/* gather grid data */
@@ -1286,7 +1295,9 @@ void multires_modifier_update_mdisps(struct DerivedMesh *dm, Scene *scene)
 			else cddm = CDDM_from_mesh(me);
 			DM_set_only_copy(cddm, CD_MASK_BAREMESH);
 
-			subdm = subsurf_dm_create_local(scene, ob, cddm, mmd->totlvl, mmd->simple, 0, mmd->uv_smooth == SUBSURF_UV_SMOOTH_NONE, has_mask, false);
+			subdm = subsurf_dm_create_local(
+			        scene, ob, cddm, mmd->totlvl, mmd->simple, 0, mmd->uv_smooth == SUBSURF_UV_SMOOTH_NONE,
+			        has_mask, false, SUBSURF_IGNORE_SIMPLIFY);
 			cddm->release(cddm);
 
 			multiresModifier_disp_run(dm, me, NULL, CALC_DISPLACEMENTS, subdm->getGridData(subdm), mmd->totlvl);
@@ -1374,11 +1385,13 @@ DerivedMesh *multires_make_derived_from_derived(DerivedMesh *dm,
 	if (lvl == 0)
 		return dm;
 
+	const int subsurf_flags = ignore_simplify ? SUBSURF_IGNORE_SIMPLIFY : 0;
+
 	result = subsurf_dm_create_local(scene, ob, dm, lvl,
 	                                 mmd->simple, mmd->flags & eMultiresModifierFlag_ControlEdges,
 	                                 mmd->uv_smooth == SUBSURF_UV_SMOOTH_NONE,
 	                                 flags & MULTIRES_ALLOC_PAINT_MASK,
-	                                 render);
+	                                 render, subsurf_flags);
 
 	if (!(flags & MULTIRES_USE_LOCAL_MMD)) {
 		ccgdm = (CCGDerivedMesh *)result;