implement selection mask with lasso tool

engine/canvas.h

@@ -64,6 +64,8 @@ public:
     std::vector<int> m_order;
     glm::vec4 m_dirty_box[6];
     bool m_dirty_face[6];
+    Layer m_smask; // selection mask
+    bool m_smask_active = false;
     RTT m_tmp[6];
     Texture2D m_tex[6];
     Texture2D m_tex2[6];
@@ -131,6 +133,7 @@ public:
     ui::Image thumbnail_read(std::string data_path);
     void preview_generate();
     void draw_objects(std::function<void(const glm::mat4& camera, const glm::mat4& proj)>);
+    void draw_objects(std::function<void(const glm::mat4& camera, const glm::mat4& proj)>, Layer& layer);
     bool ray_intersect(glm::vec3 ray_origin, glm::vec3 ray_dir, glm::vec3 plane_origin,
                           glm::vec3 plane_normal, glm::vec3 plane_tangent, glm::vec3 &out_hit);
     void point_unproject(glm::vec2 loc, glm::vec4 vp, glm::mat4 camera, glm::mat4 proj,