Fix modifiers evaluation outside of depsgraph/CoW context.

Fix T58237: Exporters: Curve Modifier not applied when "apply modifiers" are selected.
Fix T58856: Python: "to_mesh" broken in 2.8.

...And many other cases... ;)

Thing is, we need target IDs to always be evaluated ones (at least I
cannot see any case where having orig ones is desired effect here).
Depsgraph/Cow system ensures us that when modifiers are evaluated by it,
but they can also be called outside of this context, e.g. when doing
binding, or object conversion...

So we need to ensure in modifiers code that we actually are always
working with eval data for those targets.

Note that I did not touch to physics modifiers, those are a bit touchy
and rather not 'fix' something there until proven broken!

1 files changed, 6 insertions, 3 deletions

diff --git a/source/blender/modifiers/intern/MOD_surfacedeform.c b/source/blender/modifiers/intern/MOD_surfacedeform.c
index 6c6cbe3a538..d4781e419cf 100644
--- a/source/blender/modifiers/intern/MOD_surfacedeform.c
+++ b/source/blender/modifiers/intern/MOD_surfacedeform.c
@@ -1125,13 +1125,16 @@ static void surfacedeformModifier_do(
 		return;
 	}
 
-	target = BKE_modifier_get_evaluated_mesh_from_evaluated_object(smd->target, &free_target);
+	Object *ob_target = DEG_get_evaluated_object(ctx->depsgraph, smd->target);
+	target = BKE_modifier_get_evaluated_mesh_from_evaluated_object(ob_target, &free_target);
+#if 0  /* Should not be needed anymore since we always get that mesh from eval object ? */
 	if (target == NULL && smd->verts == NULL && ob == DEG_get_original_object(ob)) {
 		/* Special case, binding happens outside of depsgraph evaluation, so we can build our own
 		 * target mesh if needed. */
 		target = mesh_create_eval_final_view(ctx->depsgraph, DEG_get_input_scene(ctx->depsgraph), smd->target, 0);
 		free_target = target != NULL;
 	}
+#endif
 	if (!target) {
 		modifier_setError(md, "No valid target mesh");
 		return;
@@ -1152,7 +1155,7 @@ static void surfacedeformModifier_do(
 		float tmp_mat[4][4];
 
 		invert_m4_m4(tmp_mat, ob->obmat);
-		mul_m4_m4m4(smd->mat, tmp_mat, smd->target->obmat);
+		mul_m4_m4m4(smd->mat, tmp_mat, ob_target->obmat);
 
 		if (!surfacedeformBind(smd, vertexCos, numverts, tnumpoly, tnumverts, target)) {
 			smd->flags &= ~MOD_SDEF_BIND;
@@ -1223,7 +1226,7 @@ static bool isDisabled(const Scene *UNUSED(scene), ModifierData *md, bool UNUSED
 {
 	SurfaceDeformModifierData *smd = (SurfaceDeformModifierData *)md;
 
-	return !smd->target && !(smd->verts && !(smd->flags & MOD_SDEF_BIND));
+	return smd->target == NULL && !(smd->verts != NULL && !(smd->flags & MOD_SDEF_BIND));
 }
 
 ModifierTypeInfo modifierType_SurfaceDeform = {