;; don't using nanovg_helper lib
(bind-func draw_a_circle
(lambda ()
(nvgBeginFrame vg (convert width) (convert height) pixel_ratio)
(nvgBeginPath vg)
(nvgCircle vg 400. 400. 100.)
(nvgStrokeWidth vg 20.)
(nvgStrokeColor vg (NVGcolor 0. 1. 0. 1.))
(nvgStroke vg)
(nvgFillColor vg (NVGcolor 0. 0. 1. 1.))
(nvgFill vg)
(nvgEndFrame vg)))