default 2d lifting to y-up

viewer/glow-extras/viewer/canvas.hh

@@ -1338,7 +1338,7 @@ protected:
 
         tg::pos3 frame2d_pos;
         tg::vec3 frame2d_dir_x = tg::vec3(1, 0, 0);
-        tg::vec3 frame2d_dir_y = tg::vec3(0, 0, 1);
+        tg::vec3 frame2d_dir_y = tg::vec3(0, 0, -1);
 
         state(canvas_data& c) : points_curr{&c._points_px}, lines_curr{&c._lines_px} {}
     } _state;