;; don't using nanovg_helper lib
(bind-func draw_a_line
(lambda ()
(nvgBeginFrame vg (convert width) (convert height) pixel_ratio)
(nvgBeginPath vg)
(nvgMoveTo vg 0. 0.)
(nvgLineTo vg 400. 400.)
(nvgStrokeWidth vg 5.)
(nvgStrokeColor vg (NVGcolor 1. 0. 0. 1.))
(nvgStroke vg)
(nvgEndFrame vg)))