## Summary
- Add embedded image support to EPUB rendering with JPEG and PNG
decoders
- Implement pixel caching system to cache decoded/dithered images to SD
card for faster re-rendering
- Add 4-level grayscale support for display
## Changes
### New Image Rendering System
- Add `ImageBlock` class to represent an image with its cached path and
display dimensions
- Add `PageImage` class as a new `PageElement` type for images on pages
- Add `ImageToFramebufferDecoder` interface for format-specific image
decoders
- Add `JpegToFramebufferConverter` - JPEG decoder with Bayer dithering
and scaling
- Add `PngToFramebufferConverter` - PNG decoder with Bayer dithering and
scaling
- Add `ImageDecoderFactory` to select appropriate decoder based on file
extension
- Add `getRenderMode()` to GfxRenderer for grayscale render mode queries
### Dithering and Grayscale
- Implement 4x4 Bayer ordered dithering for 4-level grayscale output
- Stateless algorithm works correctly with MCU block decoding
- Handles scaling without artifacts
- Add grayscale render mode support (BW, GRAYSCALE_LSB, GRAYSCALE_MSB)
- Image decoders and cache renderer respect current render mode
- Enables proper 4-level e-ink grayscale when anti-aliasing is enabled
### Pixel Caching
- Cache decoded/dithered images to `.pxc` files on SD card
- Cache format: 2-bit packed pixels (4 pixels per byte) with
width/height header
- On subsequent renders, load directly from cache instead of re-decoding
- Cache renderer supports grayscale render modes for multi-pass
rendering
- Significantly improves page navigation speed for image-heavy EPUBs
### HTML Parser Integration
- Update `ChapterHtmlSlimParser` to process `<img>` tags and extract
images from EPUB
- Resolve relative image paths within EPUB ZIP structure
- Extract images to cache directory before decoding
- Create `PageImage` elements with proper scaling to fit viewport
- Fall back to alt text display if image processing fails
### Build Configuration
- Add `PNG_MAX_BUFFERED_PIXELS=6402` to support up to 800px wide images
### Test Script
- Generate test EPUBs with annotated JPEG and PNG images
- Test cases cover: grayscale (4 levels), centering, scaling, cache
performance
## Test plan
- [x] Open EPUB with JPEG images - verify images display with proper
grayscale
- [x] Open EPUB with PNG images - verify images display correctly and no
crash
- [x] Navigate away from image page and back - verify faster load from
cache
- [x] Verify grayscale tones render correctly (not just black/white
dithering)
- [x] Verify large images are scaled down to fit screen
- [x] Verify images are centered horizontally
- [x] Verify page serialization/deserialization works with images
- [x] Verify images rendered in landscape mode
## Test Results
[png](https://photos.app.goo.gl/5zFUb8xA8db3dPd19)
[jpeg](https://photos.app.goo.gl/SwtwaL2DSQwKybhw7)








---
### AI Usage
Did you use AI tools to help write this code? _**< YES >**_
---------
Co-authored-by: Matthías Páll Gissurarson <mpg@mpg.is>
Co-authored-by: Dave Allie <dave@daveallie.com>
132 lines
6.4 KiB
C++
132 lines
6.4 KiB
C++
#pragma once
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#include <EpdFontFamily.h>
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#include <HalDisplay.h>
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#include <map>
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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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void renderChar(const EpdFontFamily& fontFamily, uint32_t cp, int* x, const int* y, bool pixelState,
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EpdFontFamily::Style style) const;
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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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// 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) const;
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int getTextAdvanceX(int fontId, const char* text) 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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// 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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// 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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