2 files changed, 69 insertions, 0 deletions

diff --git a/scene/resources/mesh.cpp b/scene/resources/mesh.cpp
index 3e7b0a2808..ec9db89794 100644
--- a/scene/resources/mesh.cpp
+++ b/scene/resources/mesh.cpp
@@ -260,6 +260,64 @@ Ref<TriangleMesh> Mesh::generate_triangle_mesh() const {
 	return triangle_mesh;
 }
 
+Ref<TriangleMesh> Mesh::generate_surface_triangle_mesh(int p_surface) const {
+	ERR_FAIL_INDEX_V(p_surface, get_surface_count(), Ref<TriangleMesh>());
+
+	if (surface_triangle_meshes.size() != get_surface_count()) {
+		surface_triangle_meshes.resize(get_surface_count());
+	}
+
+	if (surface_triangle_meshes[p_surface].is_valid()) {
+		return surface_triangle_meshes[p_surface];
+	}
+
+	int facecount = 0;
+
+	if (surface_get_primitive_type(p_surface) != PRIMITIVE_TRIANGLES) {
+		return Ref<TriangleMesh>();
+	}
+
+	if (surface_get_format(p_surface) & ARRAY_FORMAT_INDEX) {
+		facecount += surface_get_array_index_len(p_surface);
+	} else {
+		facecount += surface_get_array_len(p_surface);
+	}
+
+	Vector<Vector3> faces;
+	faces.resize(facecount);
+	Vector3 *facesw = faces.ptrw();
+
+	Array a = surface_get_arrays(p_surface);
+	ERR_FAIL_COND_V(a.is_empty(), Ref<TriangleMesh>());
+
+	int vc = surface_get_array_len(p_surface);
+	Vector<Vector3> vertices = a[ARRAY_VERTEX];
+	const Vector3 *vr = vertices.ptr();
+	int widx = 0;
+
+	if (surface_get_format(p_surface) & ARRAY_FORMAT_INDEX) {
+		int ic = surface_get_array_index_len(p_surface);
+		Vector<int> indices = a[ARRAY_INDEX];
+		const int *ir = indices.ptr();
+
+		for (int j = 0; j < ic; j++) {
+			int index = ir[j];
+			facesw[widx++] = vr[index];
+		}
+
+	} else {
+		for (int j = 0; j < vc; j++) {
+			facesw[widx++] = vr[j];
+		}
+	}
+
+	Ref<TriangleMesh> triangle_mesh = Ref<TriangleMesh>(memnew(TriangleMesh));
+	triangle_mesh->create(faces);
+	surface_triangle_meshes.set(p_surface, triangle_mesh);
+
+	return triangle_mesh;
+}
+
 void Mesh::generate_debug_mesh_lines(Vector<Vector3> &r_lines) {
 	if (debug_lines.size() > 0) {
 		r_lines = debug_lines;
@@ -320,6 +378,14 @@ Vector<Face3> Mesh::get_faces() const {
 	return Vector<Face3>();
 }
 
+Vector<Face3> Mesh::get_surface_faces(int p_surface) const {
+	Ref<TriangleMesh> tm = generate_surface_triangle_mesh(p_surface);
+	if (tm.is_valid()) {
+		return tm->get_faces();
+	}
+	return Vector<Face3>();
+}
+
 Ref<Shape3D> Mesh::create_convex_shape(bool p_clean, bool p_simplify) const {
 	if (p_simplify) {
 		ConvexDecompositionSettings settings;
diff --git a/scene/resources/mesh.h b/scene/resources/mesh.h
index b166d12ead..b46a2a8a88 100644
--- a/scene/resources/mesh.h
+++ b/scene/resources/mesh.h
@@ -42,6 +42,7 @@ class Mesh : public Resource {
 	GDCLASS(Mesh, Resource);
 
 	mutable Ref<TriangleMesh> triangle_mesh; //cached
+	mutable Vector<Ref<TriangleMesh>> surface_triangle_meshes; //cached
 	mutable Vector<Vector3> debug_lines;
 	Size2i lightmap_size_hint;
 
@@ -161,7 +162,9 @@ public:
 	virtual AABB get_aabb() const;
 
 	Vector<Face3> get_faces() const;
+	Vector<Face3> get_surface_faces(int p_surface) const;
 	Ref<TriangleMesh> generate_triangle_mesh() const;
+	Ref<TriangleMesh> generate_surface_triangle_mesh(int p_surface) const;
 	void generate_debug_mesh_lines(Vector<Vector3> &r_lines);
 	void generate_debug_mesh_indices(Vector<Vector3> &r_points);