## Summary
* **What is the goal of this PR?**
Improve reliability and user experience during chapter indexing by
adding retry logic for SD card operations and a visual progress bar.
* **What changes are included?**
- **Retry logic**: Add 3 retry attempts with 50ms delay for ZIP to SD
card streaming to handle timing issues after display refresh
- **Progress bar**: Display a visual progress bar (0-100%) during
chapter indexing based on file read progress, updating every 10% to
balance responsiveness with e-ink display limitations
## Additional Context
* **Problem observed**: When navigating quickly through books with many
chapters (before chapter titles finish rendering), the "Indexing..."
screen would appear frozen. Checking the serial log revealed the
operation had silently failed, but the UI showed no indication of this.
Users would likely assume the device had crashed. Pressing the next
button again would resume operation, but this behavior was confusing and
unexpected.
* **Solution**:
- Retry logic handles transient SD card timing failures automatically,
so users don't need to manually retry
- Progress bar provides visual feedback so users know indexing is
actively working (not frozen)
* **Why timing issues occur**: After display refresh operations, there
can be timing conflicts when immediately starting SD card write
operations. This is more likely to happen when rapidly navigating
through chapters.
* **Progress bar design**: Updates every 10% to avoid excessive e-ink
refreshes while still providing meaningful feedback during long indexing
operations (especially for large chapters with CJK characters).
* **Performance**: Minimal overhead - progress calculation is simple
byte counting, and display updates use `FAST_REFRESH` mode.
## Summary
* **What is the goal of this PR?**
Replace simple threshold-based grayscale quantization with ordered
dithering using a 4x4 Bayer matrix. This eliminates color banding
artifacts and produces smoother gradients on e-ink display.
* **What changes are included?**
- Add 4x4 Bayer dithering matrix for 16-level threshold patterns
- Modify `grayscaleTo2Bit()` function to accept pixel coordinates and
apply position-based dithering
- Replace simple `grayscale >> 6` threshold with ordered dithering
algorithm that produces smoother gradients
## Additional Context
* Bayer matrix approach: The 4x4 Bayer matrix creates a repeating
pattern that distributes quantization error spatially, effectively
simulating 16 levels of gray using only 4 actual color levels (black,
dark gray, light gray, white).
* Cache invalidation: Existing cached `cover.bmp` files will need to be
deleted to see the improved rendering, as the converter only runs when
the cache is missing.
## Summary
* **What is the goal of this PR?** Fixes a bug where text disappears
after approximately 25 pages in long chapters during EPUB indexing.
* **What changes are included?**
- Removed the `MAX_LINES = 1000` hard limit in
`ParsedText::computeLineBreaks()`
- Added safer infinite loop prevention by checking if `nextBreakIndex <=
currentWordIndex` and forcing advancement by one word when stuck
## Additional Context
* **Root cause:** The `MAX_LINES = 1000` limit was introduced to prevent
infinite loops, but it truncates content in long chapters. For example,
a 93KB chapter that generates ~242 pages (~9,680 lines) gets cut off at
~1000 lines, causing blank pages after page 25-27.
* **Solution approach:** Instead of a hard line limit, I now detect when
the line break algorithm gets stuck (when `nextBreakIndex` doesn't
advance) and force progress by moving one word at a time. This preserves
the infinite loop protection while allowing all content to be rendered.
* **Testing:** Verified with a Korean EPUB containing a 93KB chapter -
all 242 pages now render correctly without text disappearing.
## Summary
* **What is the goal of this PR?**
Add a "Continue Reading" feature to improve user experience when
returning to a previously opened book.
* **What changes are included?**
- Add dynamic "Continue: <book name>" menu item in Home screen when a
book was previously opened
- File browser now starts from the folder of the last opened book
instead of always starting from root directory
- Menu dynamically shows 3 or 4 items based on reading history:
- Without history: `Browse`, `File transfer`, `Settings`
- With history: `Continue: <book>`, `Browse`, `File transfer`,
`Settings`
## Additional Context
* This feature leverages the existing `APP_STATE.openEpubPath` which
already persists the last opened book path
* The Continue Reading menu only appears if the book file still exists
on the SD card
* Book name in the menu is truncated to 25 characters with "..." suffix
if too long
* If the last book's folder was deleted, the file browser gracefully
falls back to root directory
* No new dependencies or significant memory overhead - reuses existing
state management
Replace linear O(n) search with binary search O(log n) for unicode
interval lookup. Korean fonts have many intervals (~30,000+ glyphs), so
this improves text rendering performance during page navigation.
## Summary
* **What is the goal of this PR?** (e.g., Fixes a bug in the user
authentication module, Implements the new feature for
file uploading.)
Replace linear `O(n)` glyph lookup with binary search `O(log n)` to
improve text rendering performance during page navigation.
* **What changes are included?**
- Modified `EpdFont::getGlyph()` to use binary search instead of linear
search for unicode interval lookup
- Added early return for empty interval count
## 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 implications: Fonts with many unicode intervals benefit
the most. Korean fonts have ~30,000+ glyphs across multiple intervals,
but any font with significant glyph coverage (CJK, extended Latin,
emoji, etc.) will see improvement.
- Complexity: from `O(n)` to `O(log n)` where n = number of unicode
intervals. For fonts with 10+ intervals, this reduces lookup iterations
significantly.
- Risk: Low - the binary search logic is straightforward and the
intervals are already sorted by unicode codepoint (required for the
original early-exit optimization).
Eunchurn Park