Dynamically doubling font size

jking · October 23, 2019, 1:58pm

Description

I am trying to reduce the memory usage for storing fonts. Most of my fonts are small pixel fonts, so it should be relatively easy to double the size in all dimensions at runtime, not arbitrary scaling.

Does anyone have ideas on the best way to attempt this?

What MCU/Processor/Board and compiler are you using?

Imxrt1052

What do you want to achieve?

Runtime doubling of font sizes.

What have you tried so far?

Not much, seeing if there are recommendations on where to start.

Code to reproduce

N/A

Screenshots

N/A

elgerg · October 23, 2019, 6:33pm

I too wanted to do this but ended up having to create a massive 2MB font file to include 0-9 and a colon as i wanted size 160 at 4bpp.

Ideally i would have scaled the font up but…

If anyone has any ideas or if this could be implemented i would definitely be happy to know!

Thanks
Alex

jking · October 23, 2019, 6:41pm

My hope is that there would be a way to simply multiply all of the dimensions by a scale factor during render, which for a pixelated font should be fine. I am not looking for vector based calculation to give smooth scaling.

rohmer · October 23, 2019, 7:19pm

You can create a font on the fly.

Take a look at my github. I have code for runtime serialization that may be useful as a starting point.

The font items have font in the name. I have not fully tested this section yet, but like I said it should give you an idea

rohmer · October 23, 2019, 7:20pm

Otherwise you could create a new font render engine with an option for pixel size. 1 being default. Then you could render the fonts based on that value. For bonus points you could add antialiasing. Honestly that sounds like a fun project

rohmer · October 23, 2019, 7:50pm

The more I think about this, the more I like it. If you could balance speed and size, dynamic sizing with antialiasing would be fantastic. You could define a 12 or 14 point font and dynamically size it for substantial savings in memory

embeddedt · October 23, 2019, 11:49pm

(cc @puzrin, author of the font converter)

puzrin · October 24, 2019, 12:46am

IMO bitmaps transform in runtime is not related to convertor.

rohmer · October 24, 2019, 3:05am

Oh no, I wasnt thinking it was something for the font converter

puzrin · October 24, 2019, 4:44am

@elgerg i’d suggest you try latest dev version with compression. It should be very effective on big sizes. Also, 3bpp should be enougth.

jking · October 24, 2019, 1:04pm

I have started to look at adding a multiplier to lv_draw_letter in lv_draw_basic.c.

elgerg · October 24, 2019, 7:44pm

Do you where i should put a request in for:

https://littlevgl.com/ttf-font-to-c-array

To allow for 3bpp?

Thanks
Alex

kisvegabor · October 28, 2019, 9:17am

3bpp is not supported in v6.0. It will be supported in v6.1 and then the online converter will be updated too. Until that you can use the latest version of the converter offline.

kisvegabor · October 28, 2019, 9:19am

Note that, it’s not that simple. The larger letters imply larger labels too. Probably it’d be a cleaner approach to change the callbacks of the font:

github.com

littlevgl/lvgl/blob/master/src/lv_font/lv_font.h#L59-L63


/** Get a glyph's  descriptor from a font*/
bool (*get_glyph_dsc)(const struct _lv_font_struct *, lv_font_glyph_dsc_t *, uint32_t letter, uint32_t letter_next);


/** Get a glyph's bitmap from a font*/
const uint8_t * (*get_glyph_bitmap)(const struct _lv_font_struct *, uint32_t);

tmm1 · March 10, 2020, 6:05pm

Are there any in-progress branches or PRs with this feature? I’d like to help too.

jking · March 11, 2020, 6:23pm

I kinda gave up, as I transitioned to the latest lvgl version and abandoned a lot of my customizations.

I would love if this feature could be revisited!

kisvegabor · March 11, 2020, 9:44pm

Lvgl now has functions to transform (scale and/or rotate) images. I’ve tried to apply them on glyphs but it gave quite bad quality for letters. I think it’d be reasonable to add a dedicated algorithm which scale 8 bit fonts in 0.5 … 2 range. Above 2 things gets trickier because some pixels will be skipped.

Could you contribute with algorithm like this? If so I’d integrate it to lvgl.
It’s prototype could look like:

void scale_bitmap(uint8_t * in, uint8_t out, lv_coord_t w, lv_coord_t h, uint16_t zoom);

(zoom: 256: normal, 128, half, 512 double)

What do you think?
If you are interested, please open an issue for it on GitHub.

jking · March 12, 2020, 12:28pm

My use case may not be typical, but my fonts are pixel fonts, with no antialiasing… so scaling up by whole number factors should always look perfect.

In some cases, scaling down may be possible, but my plan is to have a pixel based font in the smallest possible size to save memory space, and then scale up during runtime to the needed size.

For example this is the type of font:

kisvegabor · March 24, 2020, 7:22pm

Sorry for the late replay.

In LittlevGL I’d like to integrate a more general solution but of course locally you can add this improvement. All you need to do is to modify lv_font_get_bitmap_fmt_txt and lv_font_get_glyph_dsc_fmt_txt to returned the upscaled bitmap and coordinates.

By the way, I’ve just come across the Hqx algorithm which designed for 1 bit images. It might be useful.