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 supports two rendering backends, selected at build time:

• TinySkia (default): A lightweight software rasterizer for fast builds with no system dependencies.
• Skia: Full-featured rendering via Google Skia, used as a reference renderer.

See the Building Donner instructions for backend selection.

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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