Gradient is not working with lv.draw_rect_dsc_t

Micropython
1

Setting the gradient in lv_canvas in lv.draw_rect_dsc_t always results in black and which (the LVGL default) colors. See this canvas example:
image

The same in MP:
image

2

Strange.
It’s related specifically to bg_grad.
If I set, for example, rect_dsc.bg_color = lv.palette_main(lv.PALETTE.RED) instead of grad, then it works as expected.
I’m not sure why it behaves differently on MP, need to debug this more deeply. Maybe something related to the display driver.

3

It’s really interesting that lv.palette_main(lv.PALETTE.RED) works. Thank you for looking into it.

4

I think I know what the problem is.

A C array is converted to a Python list. Updating the list does not update back the array.
As a workaround, the whole array can be set, instead of setting individual array elements:

rect_dsc.bg_grad.stops = [
    lv.gradient_stop_t({'color': lv.palette_main(lv.PALETTE.RED)}),
    lv.gradient_stop_t({'color': lv.palette_main(lv.PALETTE.BLUE), 'frac':0xff})
]

Online example

I’ll think of ways to fix this, here is an issue to track this:

5

Great, thank you!