Add configurable letterbox fill for sleep screen cover images that don't
match the display aspect ratio. Four fill modes are available: Solid
(single dominant edge shade), Blended (per-pixel edge colors), Gradient
(edge colors interpolated toward white/black), and None.
Enable upscaling of cover images smaller than the display in Fit mode by
modifying drawBitmap/drawBitmap1Bit to support both up and downscaling
via a unified block-fill approach.
Edge sampling data is cached to .crosspoint alongside the cover BMP to
avoid redundant bitmap scanning on subsequent sleeps. Cache is validated
against screen dimensions and auto-regenerated when stale.
New settings: Letterbox Fill (None/Solid/Blended/Gradient) and Gradient
Direction (To White/To Black).
Co-authored-by: Cursor <cursoragent@cursor.com>
## Summary
* **What is the goal of this PR?** (e.g., Fixes a bug in the user
authentication module,
Display the book cover image in the **"Continue Reading"** card on the
home screen, with fast navigation using framebuffer caching.
* **What changes are included?**
- Display book cover image in the "Continue Reading" card on home screen
- Load cover from cached BMP (same as sleep screen cover)
- Add framebuffer store/restore functions (`copyStoredBwBuffer`,
`freeStoredBwBuffer`) for fast navigation after initial render
- Fix `drawBitmap` scaling bug: apply scale to offset only, not to base
coordinates
- Add white text boxes behind title/author/continue reading label for
readability on cover
- Support both EPUB and XTC file cover images
- Increase HomeActivity task stack size from 2048 to 4096 for cover
image rendering
## Additional Context
* Add any other information that might be helpful for the reviewer
(e.g., performance implications, potential risks, specific areas to
focus on).
- Performance: First render loads cover from SD card (~800ms),
subsequent navigation uses cached framebuffer (~instant)
- Memory: Framebuffer cache uses ~48KB (6 chunks × 8KB) while on home
screen, freed on exit
- Fallback: If cover image is not available, falls back to standard
text-only display
- The `drawBitmap` fix corrects a bug where screenY = (y + offset) scale
was incorrectly scaling the base coordinates. Now correctly uses screenY
= y + (offset scale)
1. Refactor Bitmap.cpp/h to expose the options for FloydSteinberg and
brightness/gamma correction at runtime
2. Fine-tune the thresholds for Floyd Steiberg and simple quantization
to better match the display's colors
Turns out that 2 is enough to make the images render properly, so the
brightness boost and gamma adjustment doesn't seem necessary currently
(at least for my test image).
