Introduction

Donner is an under-development modern C++20 SVG rendering library which provides full access to the SVG DOM, enabling browser-level functionality without the browser.

Currently, Donner includes:

• SVG2 core functionality, such as shapes, fills, strokes, and gradients.
• CSS3 parsing and cascading support, with a hand-rolled library.
• A game-engine-inspired EnTT ECS-backed document tree.
• A SVG DOM-style API to traverse, inspect, and modify documents in memory.
• A two-phase renderer, which builds and caches a rendering tree for efficient frame-based rendering.

Donner currently renders with Skia as core functionality is being implemented. While Skia is powerful, it adds a lot of code size so alternative approaches may be considered in the future.

Donner focuses on security and performance, which is validated with code coverage and fuzz testing.

Try it out: Render an SVG to PNG

bazel run --run_under="cd $PWD &&" //examples:svg_to_png -- donner_splash.svg

How it works: svg_to_png.cc

API Demo

  //! [svg_string]
  // This is the base SVG we are loading, a simple path containing a line
  const std::string_view svgContents(R"(
    <svg xmlns="http://www.w3.org/2000/svg" width="200" height="200" viewBox="0 0 10 10">
      <path d="M 1 1 L 4 5" stroke="blue" />
    </svg>
  )");
  //! [svg_string]
 
  //! [svg_parse]
  // Call ParseSVG to load the SVG file
  ParseResult<donner::svg::SVGDocument> maybeResult =
      donner::svg::parser::SVGParser::ParseSVG(svgContents);
  //! [svg_parse]
  //! [error_handling]
  if (maybeResult.hasError()) {
    std::cerr << "Parse Error " << maybeResult.error() << "\n";  // Includes line:column and reason
    std::abort();
    // - or - handle the error per your project's conventions
  }
  //! [error_handling]
 
  //! [get_path]
  donner::svg::SVGDocument document = std::move(maybeResult.result());
 
  // querySelector supports standard CSS selectors, anything that's valid when defining a CSS rule
  // works here too, for example querySelector("svg > path[fill='blue']") is also valid and will
  // match the same element.
  std::optional<donner::svg::SVGElement> maybePath = document.querySelector("path");
  UTILS_RELEASE_ASSERT_MSG(maybePath, "Failed to find path element");
 
  // The result of querySelector is a generic SVGElement, but we know it's a path, so we can cast
  // it. If the cast fails, an assertion will be triggered.
  donner::svg::SVGPathElement path = maybePath->cast<donner::svg::SVGPathElement>();
  //! [get_path]
  if (std::optional<donner::svg::PathSpline> spline = path.computedSpline()) {
    std::cout << "Path: " << *spline << "\n";
    std::cout << "Length: " << spline->pathLength() << " userspace units\n";
  } else {
    std::cout << "Path is empty\n";
  }

Detailed docs: svg_tree_interaction.cc

Documentation

• Getting Started
• System Architecture
• Devtools
• Donner API
• Examples

Project Goals

• Have minimal dependencies, so it can be integrated into existing applications, assuming a modern compiler.
• Expose the SVG DOM, so that applications can manipulate SVGs dynamically.
• Implement the SVG 2 Specification.

Status

• Project status (github)
• Build report

Building

Donner is built using Bazel, and builds are tested on Linux and macOS.

See more details in the Building Donner instructions.

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