feat: add png jpeg support (#556)
## 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>
This commit is contained in:
martin brook
committed by
GitHub
GitHub
co-authored by
Matthías Páll Gissurarson
Dave Allie
Matthías Páll Gissurarson
Dave Allie
parent
5ec4210f23
commit
ddc31546db
@@ -7,16 +7,19 @@
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#include <memory>
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#include "../ParsedText.h"
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#include "../blocks/ImageBlock.h"
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#include "../blocks/TextBlock.h"
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#include "../css/CssParser.h"
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#include "../css/CssStyle.h"
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class Page;
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class GfxRenderer;
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class Epub;
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#define MAX_WORD_SIZE 200
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class ChapterHtmlSlimParser {
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std::shared_ptr<Epub> epub;
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const std::string& filepath;
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GfxRenderer& renderer;
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std::function<void(std::unique_ptr<Page>)> completePageFn;
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@@ -43,6 +46,9 @@ class ChapterHtmlSlimParser {
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bool hyphenationEnabled;
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const CssParser* cssParser;
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bool embeddedStyle;
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std::string contentBase;
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std::string imageBasePath;
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int imageCounter = 0;
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// Style tracking (replaces depth-based approach)
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struct StyleStackEntry {
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@@ -68,15 +74,17 @@ class ChapterHtmlSlimParser {
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static void XMLCALL endElement(void* userData, const XML_Char* name);
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public:
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explicit ChapterHtmlSlimParser(const std::string& filepath, GfxRenderer& renderer, const int fontId,
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const float lineCompression, const bool extraParagraphSpacing,
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explicit ChapterHtmlSlimParser(std::shared_ptr<Epub> epub, const std::string& filepath, GfxRenderer& renderer,
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const int fontId, const float lineCompression, const bool extraParagraphSpacing,
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const uint8_t paragraphAlignment, const uint16_t viewportWidth,
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const uint16_t viewportHeight, const bool hyphenationEnabled,
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const std::function<void(std::unique_ptr<Page>)>& completePageFn,
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const bool embeddedStyle, const std::function<void()>& popupFn = nullptr,
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const bool embeddedStyle, const std::string& contentBase,
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const std::string& imageBasePath, const std::function<void()>& popupFn = nullptr,
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const CssParser* cssParser = nullptr)
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: filepath(filepath),
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: epub(epub),
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filepath(filepath),
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renderer(renderer),
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fontId(fontId),
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lineCompression(lineCompression),
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@@ -88,7 +96,9 @@ class ChapterHtmlSlimParser {
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completePageFn(completePageFn),
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popupFn(popupFn),
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cssParser(cssParser),
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embeddedStyle(embeddedStyle) {}
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embeddedStyle(embeddedStyle),
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contentBase(contentBase),
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imageBasePath(imageBasePath) {}
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~ChapterHtmlSlimParser() = default;
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bool parseAndBuildPages();
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