Strange rendering of fonts on lv_label

[igorko]

Dear LVGL Developers and Contributors,

First of all I would like to express my gratitude for this wonderful tool that you are making!
I fell in love with this library and I will be using it with all my projects. I hope very much that you will continue all your work and polish it to perfection. But it is already fully impressive!
I will gladly share my projects when any of them will be more or less mature.

I am trying to make a simple port to STM32F429 with connected E-paper display from Waveshare.
It is all success so far and LVGL draws perfectly on the display.

Till this moment I experienced only one strange behaviour when updating text on lv_label object
When started the label looks just fine:

When updated, it can randomly distort the text:

I managed to “fix” this behaviour only by setting the lv_label size to bigger than actual text:

When leaving the label’s size to default, this strange rendering happens after most of the lv_label_set_text calls.
I used only very standard features, but if you will need any details that could help to find the cause of this, I will gladly supply everything what I can.

The same goes for both build-in and custom fonts.

With very best regards, Igor

[embeddedt]

It might be an issue with your display driver. When you update the label LVGL will try to only render the changed area, which usually has a different width and height from your whole screen. Perhaps check if you have an off-by-one error in the driver as that usually causes the staggered effect.

[igorko]

Thank you very much for the hint!

I have finally solved it by adding such rounder:

void rounder(lv_disp_drv_t * disp_drv, lv_area_t *area) {
area->x1 = area->x1 & ~(0x7);
area->x2 = area->x2 | (0x7);
}