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perf: Reduce overall flash usage by 30.7% by compressing built-in fonts (#831)

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**What is the goal of this PR?**

Compress reader font bitmaps to reduce flash usage by 30.7%.

**What changes are included?**

- New `EpdFontGroup` struct and extended `EpdFontData` with
`groups`/`groupCount` fields
- `--compress` flag in `fontconvert.py`: groups glyphs (ASCII base group
+ groups of 8) and compresses each with raw DEFLATE
- `FontDecompressor` class with 4-slot LRU cache for on-demand
decompression during rendering
- `GfxRenderer` transparently routes bitmap access through
`getGlyphBitmap()` (compressed or direct flash)
- Uses `uzlib` for decompression with minimal heap overhead.
- 48 reader fonts (Bookerly, NotoSans 12-18pt, OpenDyslexic) regenerated
with compression; 5 UI fonts unchanged
- Round-trip verification script (`verify_compression.py`) runs as part
of font generation

| | baseline | font-compression | Difference |
|--|--------|-----------------|------------|
| Flash (ELF) | 6,302,476 B (96.2%) | 4,365,022 B (66.6%) | -1,937,454 B
(-30.7%) |
| firmware.bin | 6,468,192 B | 4,531,008 B | -1,937,184 B (-29.9%) |
| RAM | 101,700 B (31.0%) | 103,076 B (31.5%) | +1,376 B (+0.5%) |

Comparison of uncompressed baseline vs script-based group compression
(4-slot LRU cache, cleared each page). Glyphs are grouped by Unicode
block (ASCII, Latin-1, Latin Extended-A, Combining Marks, Cyrillic,
General Punctuation, etc.) instead of sequential groups of 8.

| | Baseline | Compressed (cold cache) | Difference |
|---|---|---|---|
| **Median** | 414.9 ms | 431.6 ms | +16.7 ms (+4.0%) |
| **Pages** | 37 | 37 | |

| | Baseline | Compressed (cold cache) | Difference |
|---|---|---|---|
| **Heap free (median)** | 187.0 KB | 176.3 KB | -10.7 KB |
| **Heap free (min)** | 186.0 KB | 166.5 KB | -19.5 KB |
| **Largest block (median)** | 148.0 KB | 128.0 KB | -20.0 KB |
| **Largest block (min)** | 148.0 KB | 120.0 KB | -28.0 KB |

| | Misses/page | Hit rate |
|---|---|---|
| **Compressed (cold cache)** | 2.1 | 99.85% |

------

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

  Did you use AI tools to help write this code? _**YES**_
Implementation was done by Claude Code (Opus 4.6) based on a plan
developed collaboratively. All generated font headers were verified with
an automated round-trip decompression test. The firmware was compiled
successfully but has not yet been tested on-device.

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Adrian Wilkins-Caruana
2026-02-19 20:30:15 +11:00
committed by cottongin
parent 6403ce6309
commit c1d1e98909
73 changed files with 126416 additions and 246010 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
lib/EpdFont/scripts/convert-builtin-fonts.sh
View File

@@ -14,7 +14,7 @@ for size in ${BOOKERLY_FONT_SIZES[@]}; do
font_name="bookerly_${size}_$(echo $style | tr '[:upper:]' '[:lower:]')"
font_path="../builtinFonts/source/Bookerly/Bookerly-${style}.ttf"
output_path="../builtinFonts/${font_name}.h"
python fontconvert.py $font_name $size $font_path --2bit > $output_path
python fontconvert.py $font_name $size $font_path --2bit --compress > $output_path
echo "Generated $output_path"
done
done
@@ -24,7 +24,7 @@ for size in ${NOTOSANS_FONT_SIZES[@]}; do
font_name="notosans_${size}_$(echo $style | tr '[:upper:]' '[:lower:]')"
font_path="../builtinFonts/source/NotoSans/NotoSans-${style}.ttf"
output_path="../builtinFonts/${font_name}.h"
python fontconvert.py $font_name $size $font_path --2bit > $output_path
python fontconvert.py $font_name $size $font_path --2bit --compress > $output_path
echo "Generated $output_path"
done
done
@@ -34,7 +34,7 @@ for size in ${OPENDYSLEXIC_FONT_SIZES[@]}; do
font_name="opendyslexic_${size}_$(echo $style | tr '[:upper:]' '[:lower:]')"
font_path="../builtinFonts/source/OpenDyslexic/OpenDyslexic-${style}.otf"
output_path="../builtinFonts/${font_name}.h"
python fontconvert.py $font_name $size $font_path --2bit > $output_path
python fontconvert.py $font_name $size $font_path --2bit --compress > $output_path
echo "Generated $output_path"
done
done
@@ -53,3 +53,7 @@ for size in ${UI_FONT_SIZES[@]}; do
done
python fontconvert.py notosans_8_regular 8 ../builtinFonts/source/NotoSans/NotoSans-Regular.ttf > ../builtinFonts/notosans_8_regular.h
echo ""
echo "Running compression verification..."
python verify_compression.py ../builtinFonts/