Add option to bake a mesh from blend shape mix

doc/classes/MeshInstance3D.xml

@@ -13,6 +13,14 @@
 		<link title="Third Person Shooter (TPS) Demo">https://godotengine.org/asset-library/asset/2710</link>
 	</tutorials>
 	<methods>
+		<method name="bake_mesh_from_current_blend_shape_mix">
+			<return type="ArrayMesh" />
+			<param index="0" name="existing" type="ArrayMesh" default="null" />
+			<description>
+				Takes a snapshot from the current [ArrayMesh] with all blend shapes applied according to their current weights and bakes it to the provided [param existing] mesh. If no [param existing] mesh is provided a new [ArrayMesh] is created, baked and returned. Mesh surface materials are not copied.
+				[b]Performance:[/b] [Mesh] data needs to be received from the GPU, stalling the [RenderingServer] in the process.
+			</description>
+		</method>
 		<method name="create_convex_collision">
 			<return type="void" />
 			<param index="0" name="clean" type="bool" default="true" />

scene/3d/mesh_instance_3d.cpp

@@ -515,6 +515,162 @@ bool MeshInstance3D::_property_get_revert(const StringName &p_name, Variant &r_p
 	return false;
 }
 
+Ref<ArrayMesh> MeshInstance3D::bake_mesh_from_current_blend_shape_mix(Ref<ArrayMesh> p_existing) {
+	Ref<ArrayMesh> source_mesh = get_mesh();
+	ERR_FAIL_NULL_V_MSG(source_mesh, Ref<ArrayMesh>(), "The source mesh must be a valid ArrayMesh.");
+
+	Ref<ArrayMesh> bake_mesh;
+
+	if (p_existing.is_valid()) {
+		ERR_FAIL_NULL_V_MSG(p_existing, Ref<ArrayMesh>(), "The existing mesh must be a valid ArrayMesh.");
+		ERR_FAIL_COND_V_MSG(source_mesh == p_existing, Ref<ArrayMesh>(), "The source mesh can not be the same mesh as the existing mesh.");
+
+		bake_mesh = p_existing;
+	} else {
+		bake_mesh.instantiate();
+	}
+
+	Mesh::BlendShapeMode blend_shape_mode = source_mesh->get_blend_shape_mode();
+	int mesh_surface_count = source_mesh->get_surface_count();
+
+	bake_mesh->clear_surfaces();
+	bake_mesh->set_blend_shape_mode(blend_shape_mode);
+
+	for (int surface_index = 0; surface_index < mesh_surface_count; surface_index++) {
+		uint32_t surface_format = source_mesh->surface_get_format(surface_index);
+
+		ERR_CONTINUE(0 == (surface_format & Mesh::ARRAY_FORMAT_VERTEX));
+
+		const Array &source_mesh_arrays = source_mesh->surface_get_arrays(surface_index);
+
+		ERR_FAIL_COND_V(source_mesh_arrays.size() != RS::ARRAY_MAX, Ref<ArrayMesh>());
+
+		const Vector<Vector3> &source_mesh_vertex_array = source_mesh_arrays[Mesh::ARRAY_VERTEX];
+		const Vector<Vector3> &source_mesh_normal_array = source_mesh_arrays[Mesh::ARRAY_NORMAL];
+		const Vector<float> &source_mesh_tangent_array = source_mesh_arrays[Mesh::ARRAY_TANGENT];
+
+		Array new_mesh_arrays;
+		new_mesh_arrays.resize(Mesh::ARRAY_MAX);
+		for (int i = 0; i < source_mesh_arrays.size(); i++) {
+			if (i == Mesh::ARRAY_VERTEX || i == Mesh::ARRAY_NORMAL || i == Mesh::ARRAY_TANGENT) {
+				continue;
+			}
+			new_mesh_arrays[i] = source_mesh_arrays[i];
+		}
+
+		bool use_normal_array = source_mesh_normal_array.size() == source_mesh_vertex_array.size();
+		bool use_tangent_array = source_mesh_tangent_array.size() / 4 == source_mesh_vertex_array.size();
+
+		Vector<Vector3> lerped_vertex_array = source_mesh_vertex_array;
+		Vector<Vector3> lerped_normal_array = source_mesh_normal_array;
+		Vector<float> lerped_tangent_array = source_mesh_tangent_array;
+
+		const Vector3 *source_vertices_ptr = source_mesh_vertex_array.ptr();
+		const Vector3 *source_normals_ptr = source_mesh_normal_array.ptr();
+		const float *source_tangents_ptr = source_mesh_tangent_array.ptr();
+
+		Vector3 *lerped_vertices_ptrw = lerped_vertex_array.ptrw();
+		Vector3 *lerped_normals_ptrw = lerped_normal_array.ptrw();
+		float *lerped_tangents_ptrw = lerped_tangent_array.ptrw();
+
+		const Array &blendshapes_mesh_arrays = source_mesh->surface_get_blend_shape_arrays(surface_index);
+		int blend_shape_count = source_mesh->get_blend_shape_count();
+		ERR_FAIL_COND_V(blendshapes_mesh_arrays.size() != blend_shape_count, Ref<ArrayMesh>());
+
+		for (int blendshape_index = 0; blendshape_index < blend_shape_count; blendshape_index++) {
+			float blend_weight = get_blend_shape_value(blendshape_index);
+			if (abs(blend_weight) <= 0.0001) {
+				continue;
+			}
+
+			const Array &blendshape_mesh_arrays = blendshapes_mesh_arrays[blendshape_index];
+
+			const Vector<Vector3> &blendshape_vertex_array = blendshape_mesh_arrays[Mesh::ARRAY_VERTEX];
+			const Vector<Vector3> &blendshape_normal_array = blendshape_mesh_arrays[Mesh::ARRAY_NORMAL];
+			const Vector<float> &blendshape_tangent_array = blendshape_mesh_arrays[Mesh::ARRAY_TANGENT];
+
+			ERR_FAIL_COND_V(source_mesh_vertex_array.size() != blendshape_vertex_array.size(), Ref<ArrayMesh>());
+			ERR_FAIL_COND_V(source_mesh_normal_array.size() != blendshape_normal_array.size(), Ref<ArrayMesh>());
+			ERR_FAIL_COND_V(source_mesh_tangent_array.size() != blendshape_tangent_array.size(), Ref<ArrayMesh>());
+
+			const Vector3 *blendshape_vertices_ptr = blendshape_vertex_array.ptr();
+			const Vector3 *blendshape_normals_ptr = blendshape_normal_array.ptr();
+			const float *blendshape_tangents_ptr = blendshape_tangent_array.ptr();
+
+			if (blend_shape_mode == Mesh::BLEND_SHAPE_MODE_NORMALIZED) {
+				for (int i = 0; i < source_mesh_vertex_array.size(); i++) {
+					const Vector3 &source_vertex = source_vertices_ptr[i];
+					const Vector3 &blendshape_vertex = blendshape_vertices_ptr[i];
+					Vector3 lerped_vertex = source_vertex.lerp(blendshape_vertex, blend_weight) - source_vertex;
+					lerped_vertices_ptrw[i] += lerped_vertex;
+
+					if (use_normal_array) {
+						const Vector3 &source_normal = source_normals_ptr[i];
+						const Vector3 &blendshape_normal = blendshape_normals_ptr[i];
+						Vector3 lerped_normal = source_normal.lerp(blendshape_normal, blend_weight) - source_normal;
+						lerped_normals_ptrw[i] += lerped_normal;
+					}
+
+					if (use_tangent_array) {
+						int tangent_index = i * 4;
+						const Vector4 source_tangent = Vector4(
+								source_tangents_ptr[tangent_index],
+								source_tangents_ptr[tangent_index + 1],
+								source_tangents_ptr[tangent_index + 2],
+								source_tangents_ptr[tangent_index + 3]);
+						const Vector4 blendshape_tangent = Vector4(
+								blendshape_tangents_ptr[tangent_index],
+								blendshape_tangents_ptr[tangent_index + 1],
+								blendshape_tangents_ptr[tangent_index + 2],
+								blendshape_tangents_ptr[tangent_index + 3]);
+						Vector4 lerped_tangent = source_tangent.lerp(blendshape_tangent, blend_weight);
+						lerped_tangents_ptrw[tangent_index] += lerped_tangent.x;
+						lerped_tangents_ptrw[tangent_index + 1] += lerped_tangent.y;
+						lerped_tangents_ptrw[tangent_index + 2] += lerped_tangent.z;
+						lerped_tangents_ptrw[tangent_index + 3] += lerped_tangent.w;
+					}
+				}
+			} else if (blend_shape_mode == Mesh::BLEND_SHAPE_MODE_RELATIVE) {
+				for (int i = 0; i < source_mesh_vertex_array.size(); i++) {
+					const Vector3 &blendshape_vertex = blendshape_vertices_ptr[i];
+					lerped_vertices_ptrw[i] += blendshape_vertex * blend_weight;
+
+					if (use_normal_array) {
+						const Vector3 &blendshape_normal = blendshape_normals_ptr[i];
+						lerped_normals_ptrw[i] += blendshape_normal * blend_weight;
+					}
+
+					if (use_tangent_array) {
+						int tangent_index = i * 4;
+						const Vector4 blendshape_tangent = Vector4(
+								blendshape_tangents_ptr[tangent_index],
+								blendshape_tangents_ptr[tangent_index + 1],
+								blendshape_tangents_ptr[tangent_index + 2],
+								blendshape_tangents_ptr[tangent_index + 3]);
+						Vector4 lerped_tangent = blendshape_tangent * blend_weight;
+						lerped_tangents_ptrw[tangent_index] += lerped_tangent.x;
+						lerped_tangents_ptrw[tangent_index + 1] += lerped_tangent.y;
+						lerped_tangents_ptrw[tangent_index + 2] += lerped_tangent.z;
+						lerped_tangents_ptrw[tangent_index + 3] += lerped_tangent.w;
+					}
+				}
+			}
+		}
+
+		new_mesh_arrays[Mesh::ARRAY_VERTEX] = lerped_vertex_array;
+		if (use_normal_array) {
+			new_mesh_arrays[Mesh::ARRAY_NORMAL] = lerped_normal_array;
+		}
+		if (use_tangent_array) {
+			new_mesh_arrays[Mesh::ARRAY_TANGENT] = lerped_tangent_array;
+		}
+
+		bake_mesh->add_surface_from_arrays(Mesh::PRIMITIVE_TRIANGLES, new_mesh_arrays, Array(), Dictionary(), surface_format);
+	}
+
+	return bake_mesh;
+}
+
 void MeshInstance3D::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("set_mesh", "mesh"), &MeshInstance3D::set_mesh);
 	ClassDB::bind_method(D_METHOD("get_mesh"), &MeshInstance3D::get_mesh);
@@ -542,6 +698,9 @@ void MeshInstance3D::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("set_blend_shape_value", "blend_shape_idx", "value"), &MeshInstance3D::set_blend_shape_value);
 
 	ClassDB::bind_method(D_METHOD("create_debug_tangents"), &MeshInstance3D::create_debug_tangents);
+
+	ClassDB::bind_method(D_METHOD("bake_mesh_from_current_blend_shape_mix", "existing"), &MeshInstance3D::bake_mesh_from_current_blend_shape_mix, DEFVAL(Ref<ArrayMesh>()));
+
 	ADD_PROPERTY(PropertyInfo(Variant::OBJECT, "mesh", PROPERTY_HINT_RESOURCE_TYPE, "Mesh"), "set_mesh", "get_mesh");
 	ADD_GROUP("Skeleton", "");
 	ADD_PROPERTY(PropertyInfo(Variant::OBJECT, "skin", PROPERTY_HINT_RESOURCE_TYPE, "Skin"), "set_skin", "get_skin");

scene/3d/mesh_instance_3d.h

@@ -101,6 +101,8 @@ class MeshInstance3D : public GeometryInstance3D {
 
 	virtual AABB get_aabb() const override;
 
+	Ref<ArrayMesh> bake_mesh_from_current_blend_shape_mix(Ref<ArrayMesh> p_existing = Ref<ArrayMesh>());
+
 	MeshInstance3D();
 	~MeshInstance3D();
 };