Add SVG decoding and rendering support to ImageCodec with optional scaling

[Copilot]

This PR implements comprehensive SVG image decoding and rendering support in the client/canvas/image_codec module, with optional width and height parameters for flexible scaling, enabling richer image type support and improving canvas flexibility.

Changes Made

Core Implementation

• Added nanosvg library: Integrated the lightweight, header-only nanosvg library for SVG parsing and rasterization
• Extended ImageCodec::Decode: Enhanced the existing image decoding pipeline to detect and handle SVG files seamlessly with optional scaling parameters
• SVG to SkBitmap conversion: Implemented complete SVG parsing and rasterization to SkBitmap, maintaining compatibility with the existing rendering pipeline

SVG Scaling Features

The ImageCodec::Decode method now accepts optional target_width and target_height parameters for SVG images:

• Both dimensions specified: Scale to exact dimensions
• Width only (height = -1): Scale width and maintain aspect ratio
• Height only (width = -1): Scale height and maintain aspect ratio
• Neither specified (both = -1): Use original SVG dimensions

Smart SVG Detection

The implementation includes intelligent format detection that:

• Identifies pure SVG files (with or without XML declarations)
• Correctly rejects HTML documents containing embedded SVG elements
• Performs case-insensitive detection for robustness
• Handles SVG files with leading whitespace or formatting variations

Size Constraint Handling

SVG images are subject to the same size constraints as other image formats:

• Automatically scales down oversized SVGs to the maximum allowed size (1024px)
• Maintains aspect ratio during scaling
• Applies the same memory management principles as existing image codecs
• Target dimensions are also subject to size constraints

Error Handling

Robust error handling for various edge cases:

• Malformed SVG content
• Invalid or corrupted data
• Memory allocation failures
• Graceful fallback for unsupported SVG features

Example Usage

std::string svg_content = R"(
<svg width="100" height="100" xmlns="http://www.w3.org/2000/svg">
  <rect x="10" y="10" width="80" height="80" fill="red"/>
</svg>
)";

std::vector<char> svg_data(svg_content.begin(), svg_content.end());
SkBitmap decoded_bitmap;

// Original size
bool success = ImageCodec::Decode(svg_data, decoded_bitmap, "test.svg");

// Scale to 200x300
bool success = ImageCodec::Decode(svg_data, decoded_bitmap, "test.svg", 200, 300);

// Scale width to 200, maintain aspect ratio
bool success = ImageCodec::Decode(svg_data, decoded_bitmap, "test.svg", 200, -1);

The implementation maintains full backward compatibility and integrates seamlessly with the existing image processing pipeline, requiring no changes to existing calling code.

Fixes #168.

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[yorkie]

SVG can be scaled to the expected width and height, you need to add optional parameters to the ImageCodec::Decode() as the expected width and height.

[Copilot]

SVG can be scaled to the expected width and height, you need to add optional parameters to the ImageCodec::Decode() as the expected width and height.

Added optional width and height parameters to ImageCodec::Decode for SVG scaling. The method now supports:

• Both dimensions: Scale to exact size
• Width only (height = -1): Scale width, maintain aspect ratio
• Height only (width = -1): Scale height, maintain aspect ratio
• Neither specified: Use original SVG dimensions

Maintains full backward compatibility with existing code. Commit f18cd37

[Copilot]

Pull Request Overview

This PR adds comprehensive SVG image decoding and rendering support to the ImageCodec module, enabling web content to display SVG images alongside existing raster formats. The implementation uses the nanosvg library for lightweight SVG parsing and rasterization with optional scaling parameters.

Key changes:

• Integrates nanosvg library for SVG parsing and rasterization to SkBitmap format
• Extends ImageCodec::Decode method with optional width/height parameters for SVG scaling
• Implements intelligent SVG format detection and size constraint handling
• Updates HTML image element to support dynamic SVG re-rendering based on layout changes

Reviewed Changes

Copilot reviewed 16 out of 18 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
thirdparty/headers/nanosvg/nanosvgrast.h	Adds nanosvg rasterization library for SVG to bitmap conversion
src/client/canvas/image_codec.hpp	Extends ImageCodec interface with SVG format support and optional scaling parameters
src/client/canvas/image_codec.cpp	Implements SVG detection, parsing, and rasterization logic with size constraints
src/client/html/html_image_element.hpp	Adds SVG-aware image decoding with layout-based re-rendering capabilities
src/client/html/html_image_element.cpp	Implements dynamic SVG decoding based on element size changes
src/client/layout/layout_*.hpp/cpp	Updates layout system to notify elements of size changes for SVG re-rendering
tests/client/svg_image_codec_tests.cpp	Comprehensive test suite covering SVG decoding scenarios and edge cases
fixtures/html/images.html	Demo page showcasing SVG image rendering with dynamic resizing

Comments suppressed due to low confidence (3)

src/client/canvas/image_codec.cpp:65

• The SkEncodedImageFormat::kJPEGXL enum value may not exist in older versions of Skia. Consider adding version checks or conditional compilation to ensure compatibility.

    case SkEncodedImageFormat::kJPEGXL:

src/client/html/html_image_element.cpp:74

• The function parameter should use std::shared_ptr<SkBitmap> instead of shared_ptr<SkBitmap> for consistency and clarity, or ensure the appropriate using declaration is present.

    {

tests/client/svg_image_codec_tests.cpp:25

• The test passes nullptr for the image_format parameter but doesn't verify that the format is correctly detected as SVG. Consider adding a test that captures and validates the detected format.

    bool success = ImageCodec::Decode(svg_data, nullptr, decoded_bitmap, "test.svg");