Shadows don't update when changing blend shape values

[RedMser]

Tested versions

Reproducible in 2ba22d1 (custom build from 2 days ago)

System information

Windows 10.0.19044 - dedicated NVIDIA GeForce RTX 2080 (NVIDIA; 31.0.15.5186) - Intel(R) Core(TM) i7-8700K CPU @ 3.70GHz (12 Threads)

Issue description

If you change a MeshInstance's blend shapes using code set_blend_shape_value in e.g. _process, then shadows of an OmniLight3D will not update until you also move the mesh (e.g. by nudging the position value slightly).

This happens in Compatibility, Mobile and Forward+ renderers.

Steps to reproduce

See above.

Minimal reproduction project (MRP)

blend-shapes-dont-update-shadows.zip

The cube is animated via blend shapes only. Uncommenting the last line in the cube's script will fix shadows not updating. Change renderer to any other and observe the same problem.

[clayjohn]

This will need a bit of investigation to track down. But I think there is one of three things to look for:

1. We may need to notify the dependency system that the variable changed like we do for skeletons:
   

   godot/servers/rendering/renderer_rd/storage_rd/mesh_storage.cpp

   Line 2293 in c4279fe

   skeleton->dependency.changed_notify(Dependency::DEPENDENCY_CHANGED_SKELETON_BONES);

2. We may need to set the instance to dirty some other way when updating blend shapes. Maybe here:
   

   godot/servers/rendering/renderer_rd/storage_rd/mesh_storage.cpp

   Lines 917 to 924 in c4279fe

   	void MeshStorage::mesh_instance_set_blend_shape_weight(RID p_mesh_instance, int p_shape, float p_weight) {
   	MeshInstance *mi = mesh_instance_owner.get_or_null(p_mesh_instance);
   	ERR_FAIL_NULL(mi);
   	ERR_FAIL_INDEX(p_shape, (int)mi->blend_weights.size());
   	mi->blend_weights[p_shape] = p_weight;
   	mi->weights_dirty = true;
   	//will be eventually updated
   	}

For context instance_set_blend_shape_weight() will try to update the instance if it is already dirty.

godot/servers/rendering/renderer_scene_cull.cpp

Lines 950 to 961 in c4279fe

	void RendererSceneCull::instance_set_blend_shape_weight(RID p_instance, int p_shape, float p_weight) {
	Instance *instance = instance_owner.get_or_null(p_instance);
	ERR_FAIL_NULL(instance);
	if (instance->update_item.in_list()) {
	_update_dirty_instance(instance);
	}
	if (instance->mesh_instance.is_valid()) {
	RSG::mesh_storage->mesh_instance_set_blend_shape_weight(instance->mesh_instance, p_shape, p_weight);
	}
	}

If the instance is flagged as dirty, then we will mark the shadows as dirty. But we could also do it manually when blend shapes are modified:

godot/servers/rendering/renderer_scene_cull.cpp

Lines 884 to 889 in c4279fe

	if (geom->can_cast_shadows) {
	for (HashSet<RendererSceneCull::Instance *>::Iterator I = geom->lights.begin(); I != geom->lights.end(); ++I) {
	InstanceLightData *light = static_cast<InstanceLightData *>((*I)->base_data);
	light->make_shadow_dirty();
	}
	}