How to use lv_canvas_draw_line() in Micropython?

Micropython
1

Hi,

The definition of lv_canvas_draw_line is:

void lv_canvas_draw_line(lv_obj_t *canvas, const lv_point_t points[], uint32_t point_cnt, lv_draw_line_dsc_t *line_draw_dsc)

The second arg is an array of lv_point_t, how should I pass the array in micropython?

I have tried tuple and list but both failed:

canv = lv.canvas()
p1 = lv.point_t()
p2 = lv.point_t()
p1.x = 100
p1.y = 100
p2.x = 300
p2.y = 300
canv.draw_line((p1,p2), 2, style) # failed
canv.draw_line([p1, p2], 2, style) #failed

Thanks.

2

Good catch. It’s a bug.

The draw_line C prototype is

void lv_canvas_draw_line(lv_obj_t * canvas, const lv_point_t * points, uint32_t point_cnt, const lv_style_t * style);

It should change to:

void lv_canvas_draw_line(lv_obj_t * canvas, const lv_point_t points[], uint32_t point_cnt, const lv_style_t * style);

For C, passing const lv_point_t * points or const lv_point_t points[] is the same.
But the micropython bindings use that as a hint that this is an array and not a pointer.

Until this is fixed on GitHub you can try changing it locally and see if it solves your problem.
After that, canv.draw_line([p1, p2], 2, style) should work.

3

Fixed (including some other similar cases) on https://github.com/lvgl/lvgl/pull/1633

4

Thanks for fixing it.