## Summary **What is the goal of this PR?** Hopefully fixes #1182. _Note: I think letterforms got a "heavier" appearance after #1098, which makes this more noticeable. The current version of this PR reverts the change to add `--force-autohint` for Bookerly, which to me seems to bring the font back to a more aesthetic and consistent weight._ #### Problem Character spacing was uneven in certain words. The word "drew" in Bookerly was the clearest example: a visible gap between `d` and `r`, while `e` and `w` appeared tightly condensed. The root cause was twofold: 1. **Integer-only glyph advances.** `advanceX` was stored as a `uint8_t` of whole pixels, sourced from FreeType's hinted `advance.x` (which grid-fits to integers). A glyph whose true advance is 15.56px was stored as 16px -- an error of +0.44px per character that compounds across a line. 2. **Floor-rounded kerning.** Kern adjustments were converted with `math.floor()`, which systematically over-tightened negative kerns. A kern of -0.3px became -1px -- a 0.7px over-correction that visibly closed gaps. Combined, these produced the classic symptom: some pairs too wide, others too tight, with the imbalance varying per word. #### Solution: fixed-point accumulation with 1/16-pixel resolution, for sub-pixel precision during text layout All font metrics now use a "fixed-point 4" format -- 4 fractional bits giving 1/16-pixel (0.0625px) resolution. This is implemented with plain integer arithmetic (shifts and adds), requiring no floating-point on the ESP32. **How it works:** A value like 15.56px is stored as the integer `249`: ``` 249 = 15 * 16 + 9 (where 9/16 = 0.5625, closest to 0.56) ``` Two storage widths share the same 4 fractional bits: | Field | Type | Format | Range | Use | |-------|------|--------|-------|-----| | `advanceX` | `uint16_t` | 12.4 | 0 -- 4095.9375 px | Glyph advance width | | `kernMatrix` | `int8_t` | 4.4 | -8.0 -- +7.9375 px | Kerning adjustment | Because both have 4 fractional bits, they add directly into a single `int32_t` accumulator during layout. The accumulator is only snapped to the nearest whole pixel at the moment each glyph is rendered: ```cpp int32_t xFP = fp4::fromPixel(startX); // pixel to 12.4: startX << 4 for each character: xFP += kernFP; // add 4.4 kern (sign-extends into int32_t) int xPx = fp4::toPixel(xFP); // snap to nearest pixel: (xFP + 8) >> 4 render glyph at xPx; xFP += glyph->advanceX; // add 12.4 advance ``` Fractional remainders carry forward indefinitely. Rounding errors stay below +/- 0.5px and never compound. #### Concrete example: "drew" in Bookerly **Before** (integer advances, floor-rounded kerning): | Char | Advance | Kern | Cursor | Snap | Gap from prev | |------|---------|------|--------|------|---------------| | d | 16 px | -- | 33 | 33 | -- | | r | 12 px | 0 | 49 | 49 | ~2px | | e | 13 px | -1 | 60 | 60 | ~0px | | w | 22 px | -1 | 72 | 72 | ~0px | The d-to-r gap was visibly wider than the tightly packed `rew`. **After** (12.4 advances, 4.4 kerning, fractional accumulation): | Char | Advance (FP) | Kern (FP) | Accumulator | Snap | Ink start | Gap from prev | |------|-------------|-----------|-------------|------|-----------|---------------| | d | 249 (15.56px) | -- | 528 | 33 | 34 | -- | | r | 184 (11.50px) | 0 | 777 | 49 | 49 | 0px | | e | 208 (13.00px) | -8 (-0.50px) | 953 | 60 | 61 | 1px | | w | 356 (22.25px) | -4 (-0.25px) | 1157 | 72 | 72 | 0px | Spacing is now `0, 1, 0` pixels -- nearly uniform. Verified on-device: all 5 copies of "drew" in the test EPUB produce identical spacing, confirming zero accumulator drift. #### Changes **Font conversion (`fontconvert.py`)** - Use `linearHoriAdvance` (FreeType 16.16, unhinted) instead of `advance.x` (26.6, grid-fitted to integers) for glyph advances - Encode kern values as 4.4 fixed-point with `round()` instead of `floor()` - Add `fp4_from_ft16_16()` and `fp4_from_design_units()` helper functions - Add module-level documentation of fixed-point conventions **Font data structures (`EpdFontData.h`)** - `EpdGlyph::advanceX`: `uint8_t` to `uint16_t` (no memory cost due to existing struct padding) - Add `fp4` namespace with `constexpr` helpers: `fromPixel()`, `toPixel()`, `toFloat()` - Document fixed-point conventions **Font API (`EpdFont.h/cpp`, `EpdFontFamily.h/cpp`)** - `getKerning()` return type: `int8_t` to `int` (to avoid truncation of the 4.4 value) **Rendering (`GfxRenderer.cpp`)** - `drawText()`: replace integer cursor with `int32_t` fixed-point accumulator - `drawTextRotated90CW()`: same accumulator treatment for vertical layout - `getTextAdvanceX()`, `getSpaceWidth()`, `getSpaceKernAdjust()`, `getKerning()`: convert from fixed-point to pixel at API boundary **Regenerated all built-in font headers** with new 12.4 advances and 4.4 kern values. #### Memory impact Zero additional RAM. The `advanceX` field grew from `uint8_t` to `uint16_t`, but the `EpdGlyph` struct already had 1 byte of padding at that position, so the struct size is unchanged. The fixed-point accumulator is a single `int32_t` on the stack. #### Test plan - [ ] Verify "drew" spacing in Bookerly at small, medium, and large sizes - [ ] Verify uppercase kerning pairs: AVERY, WAVE, VALUE - [ ] Verify ligature words: coffee, waffle, office - [ ] Verify all built-in fonts render correctly at each size - [ ] Verify rotated text (progress bar percentage) renders correctly - [ ] Verify combining marks (accented characters) still position correctly - [ ] Spot-check a full-length book for any layout regressions --- ### AI Usage 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, Claude Opus 4.6 helped figure out a non-floating point approach for sub-pixel error accumulation**_
151 lines
7.5 KiB
C++
151 lines
7.5 KiB
C++
#pragma once
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#include <EpdFontFamily.h>
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#include <FontDecompressor.h>
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#include <HalDisplay.h>
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#include <map>
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#include <string>
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#include <vector>
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#include "Bitmap.h"
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// Color representation: uint8_t mapped to 4x4 Bayer matrix dithering levels
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// 0 = transparent, 1-16 = gray levels (white to black)
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enum Color : uint8_t { Clear = 0x00, White = 0x01, LightGray = 0x05, DarkGray = 0x0A, Black = 0x10 };
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class GfxRenderer {
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public:
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enum RenderMode { BW, GRAYSCALE_LSB, GRAYSCALE_MSB };
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// Logical screen orientation from the perspective of callers
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enum Orientation {
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Portrait, // 480x800 logical coordinates (current default)
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LandscapeClockwise, // 800x480 logical coordinates, rotated 180° (swap top/bottom)
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PortraitInverted, // 480x800 logical coordinates, inverted
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LandscapeCounterClockwise // 800x480 logical coordinates, native panel orientation
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};
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private:
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static constexpr size_t BW_BUFFER_CHUNK_SIZE = 8000; // 8KB chunks to allow for non-contiguous memory
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static constexpr size_t BW_BUFFER_NUM_CHUNKS = HalDisplay::BUFFER_SIZE / BW_BUFFER_CHUNK_SIZE;
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static_assert(BW_BUFFER_CHUNK_SIZE * BW_BUFFER_NUM_CHUNKS == HalDisplay::BUFFER_SIZE,
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"BW buffer chunking does not line up with display buffer size");
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HalDisplay& display;
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RenderMode renderMode;
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Orientation orientation;
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bool fadingFix;
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uint8_t* frameBuffer = nullptr;
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uint8_t* bwBufferChunks[BW_BUFFER_NUM_CHUNKS] = {nullptr};
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std::map<int, EpdFontFamily> fontMap;
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FontDecompressor* fontDecompressor = nullptr;
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void freeBwBufferChunks();
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template <Color color>
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void drawPixelDither(int x, int y) const;
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template <Color color>
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void fillArc(int maxRadius, int cx, int cy, int xDir, int yDir) const;
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public:
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explicit GfxRenderer(HalDisplay& halDisplay)
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: display(halDisplay), renderMode(BW), orientation(Portrait), fadingFix(false) {}
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~GfxRenderer() { freeBwBufferChunks(); }
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static constexpr int VIEWABLE_MARGIN_TOP = 9;
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static constexpr int VIEWABLE_MARGIN_RIGHT = 3;
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static constexpr int VIEWABLE_MARGIN_BOTTOM = 3;
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static constexpr int VIEWABLE_MARGIN_LEFT = 3;
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// Setup
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void begin(); // must be called right after display.begin()
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void insertFont(int fontId, EpdFontFamily font);
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void setFontDecompressor(FontDecompressor* d) { fontDecompressor = d; }
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void clearFontCache() {
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if (fontDecompressor) fontDecompressor->clearCache();
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}
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// Orientation control (affects logical width/height and coordinate transforms)
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void setOrientation(const Orientation o) { orientation = o; }
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Orientation getOrientation() const { return orientation; }
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// Fading fix control
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void setFadingFix(const bool enabled) { fadingFix = enabled; }
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// Screen ops
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int getScreenWidth() const;
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int getScreenHeight() const;
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void displayBuffer(HalDisplay::RefreshMode refreshMode = HalDisplay::FAST_REFRESH) const;
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// EXPERIMENTAL: Windowed update - display only a rectangular region
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// void displayWindow(int x, int y, int width, int height) const;
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void invertScreen() const;
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void clearScreen(uint8_t color = 0xFF) const;
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void getOrientedViewableTRBL(int* outTop, int* outRight, int* outBottom, int* outLeft) const;
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// Drawing
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void drawPixel(int x, int y, bool state = true) const;
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void drawLine(int x1, int y1, int x2, int y2, bool state = true) const;
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void drawLine(int x1, int y1, int x2, int y2, int lineWidth, bool state) const;
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void drawArc(int maxRadius, int cx, int cy, int xDir, int yDir, int lineWidth, bool state) const;
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void drawRect(int x, int y, int width, int height, bool state = true) const;
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void drawRect(int x, int y, int width, int height, int lineWidth, bool state) const;
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void drawRoundedRect(int x, int y, int width, int height, int lineWidth, int cornerRadius, bool state) const;
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void drawRoundedRect(int x, int y, int width, int height, int lineWidth, int cornerRadius, bool roundTopLeft,
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bool roundTopRight, bool roundBottomLeft, bool roundBottomRight, bool state) const;
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void fillRect(int x, int y, int width, int height, bool state = true) const;
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void fillRectDither(int x, int y, int width, int height, Color color) const;
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void fillRoundedRect(int x, int y, int width, int height, int cornerRadius, Color color) const;
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void fillRoundedRect(int x, int y, int width, int height, int cornerRadius, bool roundTopLeft, bool roundTopRight,
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bool roundBottomLeft, bool roundBottomRight, Color color) const;
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void drawImage(const uint8_t bitmap[], int x, int y, int width, int height) const;
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void drawIcon(const uint8_t bitmap[], int x, int y, int width, int height) const;
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void drawBitmap(const Bitmap& bitmap, int x, int y, int maxWidth, int maxHeight, float cropX = 0,
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float cropY = 0) const;
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void drawBitmap1Bit(const Bitmap& bitmap, int x, int y, int maxWidth, int maxHeight) const;
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void fillPolygon(const int* xPoints, const int* yPoints, int numPoints, bool state = true) const;
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// Text
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int getTextWidth(int fontId, const char* text, EpdFontFamily::Style style = EpdFontFamily::REGULAR) const;
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void drawCenteredText(int fontId, int y, const char* text, bool black = true,
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EpdFontFamily::Style style = EpdFontFamily::REGULAR) const;
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void drawText(int fontId, int x, int y, const char* text, bool black = true,
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EpdFontFamily::Style style = EpdFontFamily::REGULAR) const;
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int getSpaceWidth(int fontId, EpdFontFamily::Style style = EpdFontFamily::REGULAR) const;
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/// Returns the kerning adjustment for a space between two codepoints:
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/// kern(leftCp, ' ') + kern(' ', rightCp). Returns 0 if kerning is unavailable.
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int getSpaceKernAdjust(int fontId, uint32_t leftCp, uint32_t rightCp, EpdFontFamily::Style style) const;
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/// Returns the kerning adjustment between two adjacent codepoints.
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int getKerning(int fontId, uint32_t leftCp, uint32_t rightCp, EpdFontFamily::Style style) const;
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int getTextAdvanceX(int fontId, const char* text, EpdFontFamily::Style style) const;
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int getFontAscenderSize(int fontId) const;
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int getLineHeight(int fontId) const;
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std::string truncatedText(int fontId, const char* text, int maxWidth,
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EpdFontFamily::Style style = EpdFontFamily::REGULAR) const;
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/// Word-wrap \p text into at most \p maxLines lines, each no wider than
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/// \p maxWidth pixels. Overflowing words and excess lines are UTF-8-safely
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/// truncated with an ellipsis (U+2026).
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std::vector<std::string> wrappedText(int fontId, const char* text, int maxWidth, int maxLines,
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EpdFontFamily::Style style = EpdFontFamily::REGULAR) const;
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// Helper for drawing rotated text (90 degrees clockwise, for side buttons)
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void drawTextRotated90CW(int fontId, int x, int y, const char* text, bool black = true,
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EpdFontFamily::Style style = EpdFontFamily::REGULAR) const;
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int getTextHeight(int fontId) const;
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// Grayscale functions
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void setRenderMode(const RenderMode mode) { this->renderMode = mode; }
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RenderMode getRenderMode() const { return renderMode; }
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void copyGrayscaleLsbBuffers() const;
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void copyGrayscaleMsbBuffers() const;
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void displayGrayBuffer() const;
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bool storeBwBuffer(); // Returns true if buffer was stored successfully
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void restoreBwBuffer(); // Restore and free the stored buffer
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void cleanupGrayscaleWithFrameBuffer() const;
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// Font helpers
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const uint8_t* getGlyphBitmap(const EpdFontData* fontData, const EpdGlyph* glyph) const;
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// Low level functions
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uint8_t* getFrameBuffer() const;
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static size_t getBufferSize();
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};
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