6c3a615fac
## 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>
37 lines
1.2 KiB
C++
37 lines
1.2 KiB
C++
#pragma once
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#include <EpdFontFamily.h>
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#include <HalStorage.h>
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#include <list>
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#include <memory>
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#include <string>
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#include "Block.h"
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#include "BlockStyle.h"
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// Represents a line of text on a page
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class TextBlock final : public Block {
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private:
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std::list<std::string> words;
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std::list<uint16_t> wordXpos;
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std::list<EpdFontFamily::Style> wordStyles;
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BlockStyle blockStyle;
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public:
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explicit TextBlock(std::list<std::string> words, std::list<uint16_t> word_xpos,
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std::list<EpdFontFamily::Style> word_styles, const BlockStyle& blockStyle = BlockStyle())
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: words(std::move(words)),
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wordXpos(std::move(word_xpos)),
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wordStyles(std::move(word_styles)),
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blockStyle(blockStyle) {}
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~TextBlock() override = default;
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void setBlockStyle(const BlockStyle& blockStyle) { this->blockStyle = blockStyle; }
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const BlockStyle& getBlockStyle() const { return blockStyle; }
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bool isEmpty() override { return words.empty(); }
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// given a renderer works out where to break the words into lines
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void render(const GfxRenderer& renderer, int fontId, int x, int y) const;
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BlockType getType() override { return TEXT_BLOCK; }
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bool serialize(FsFile& file) const;
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static std::unique_ptr<TextBlock> deserialize(FsFile& file);
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};
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