Ugly font display with monochrome device

How-to
1

Hello,

I’m using lvgl from master branch (but same with 9.2.2) with a 128x64 monochrome display.

As the arrangement of the pixels in memory is “different”, I had to develop my own conversion routine.
So far, so good, it seems with some tests that it works as it should.

20250126_103637_resize
20250126_103637_resize1024×768 192 KB

Now, I tried 2 others tests:

  • Line from top-left corner to bottom-right: As the display is exactly twice wider than height, I expected a regular line which is not the case. It is thicker in the middle:

Sorry, some pictures will be posted in some answers. As a new user, I’m not allowed to post more than 2 attachments

  • A text: Font is montserrat_20. I expected a more regular shape.

20250126_103914_resize
20250126_103914_resize1024×768 195 KB

As a comparison, here’s what I was able to get with LVGL8 and a 200x200 display -better definition though- but with a smaller font montserrat 16 for the smaller text. To me it looks far better.

I must have missed something in my code. I looked at how to disable antialiasing for example, but it looks that this is already taken care of by the library.
So what’s wrong?

I join the conf.h file.

Here’s the initialisation code:

void display__init() {
    lv_init();

    lv_display_t *display = lv_display_create(WIDTH, HEIGHT);
    lv_display_set_color_format(display, LV_COLOR_FORMAT_I1);

    lv_display_set_rotation(display, LV_DISPLAY_ROTATION_0);

    lv_display_set_buffers(display, buffer_lvgl, NULL, sizeof(buffer_lvgl), LV_DISPLAY_RENDER_MODE_FULL);
    lv_display_set_flush_cb(display, my_flush_cb);
    lv_display_add_event_cb(display, my_rounder_cb, LV_EVENT_INVALIDATE_AREA, display);
    m_default_scr = lv_disp_get_scr_act(NULL);

    //--- label
    lblAltitude = lv_label_create(m_default_scr);
    lv_label_set_text(lblAltitude, "rotation 2");
    lv_obj_set_width(lblAltitude, 100);
    lv_obj_set_x(lblAltitude, 10);
    lv_obj_set_y(lblAltitude, 10);

    lv_scr_load(m_default_scr);

    lv_task_handler();

Thanks for your help
Julien
lv_conf.h (25.2 KB)

2

Missing pictures from previous post:

Diagonal line:

20250126_103828_resize
20250126_103828_resize1024×768 172 KB

Other display lvgl8:

20230710_204109
20230710_204109961×947 168 KB

3

Hello,

small follow-up in case anybody needs it.
I built a custom 1bit font from montserrat ttf and the result is better in my opinion. I also choosed the medium variant of the font.

20250127_134611_resize
20250127_134611_resize1000×750 140 KB

4

Hi Julien,

Have you tried UNSCII_8 and UNSCII_16 for the monochrome display?

This is very useful if you want to create your own font:
https://www.pentacom.jp/pentacom/bitfontmaker2

5

disable anti-alias

6

Hi Marton,

I found UNSCII_8 too fat for my use.

Very interesting website!

Thanks for your help.
Julien

7

Hello

Do you have any advice on how to do it?

Thanks
Julien

8

I would have to look at the code as well. It could be disabled based on the color depth. However it doesn’t look like it is from your example image.

You should be able to change it by changing the field value for it in lv_display_t (lv_disp_t prior to V9).