hyper-render

A Chromium-free HTML rendering engine for generating PNG and PDF outputs in pure Rust.

Features

No browser required — Pure Rust implementation, no Chromium/WebKit dependency
PNG output — High-quality raster images via CPU-based rendering
PDF output — Vector PDF documents with embedded fonts
Modern CSS — Flexbox, Grid, and common CSS properties via Stylo (Firefox's CSS engine)
Simple API — Single function call to render HTML to bytes

Installation

Add to your Cargo.toml:

[dependencies]
hyper-render = "0.1"

Or with specific features:

[dependencies]
hyper-render = { version = "0.1", default-features = false, features = ["png"] }

Quick Start

use hyper_render::{render, Config, OutputFormat};

fn main() -> Result<(), hyper_render::Error> {
    let html = r#"
        <html>
        <body style="font-family: sans-serif; padding: 20px;">
            <h1 style="color: navy;">Hello, World!</h1>
            <p>Rendered without Chromium.</p>
        </body>
        </html>
    "#;

    // Render to PNG
    let png_bytes = render(html, Config::default())?;
    std::fs::write("output.png", png_bytes)?;

    // Render to PDF
    let pdf_bytes = render(html, Config::new().format(OutputFormat::Pdf))?;
    std::fs::write("output.pdf", pdf_bytes)?;

    Ok(())
}

API

Main Functions

// Render to any format based on config
render(html: &str, config: Config) -> Result<Vec<u8>>

// Convenience functions
render_to_png(html: &str, config: Config) -> Result<Vec<u8>>
render_to_pdf(html: &str, config: Config) -> Result<Vec<u8>>

Configuration

use hyper_render::{Config, OutputFormat, ColorScheme};

let config = Config::new()
    .width(1200)              // Viewport width in pixels
    .height(800)              // Viewport height in pixels
    .size(1200, 800)          // Set both at once
    .scale(2.0)               // Scale factor (2.0 for retina)
    .format(OutputFormat::Png) // Output format: Png or Pdf
    .color_scheme(ColorScheme::Light) // Light or Dark mode
    .auto_height(true)        // Auto-detect content height
    .background([255, 255, 255, 255]) // RGBA background color
    .transparent();           // Transparent background

Output Formats

Format	Status	Description
`OutputFormat::Png`	✅ Full	Raster image via Vello CPU renderer
`OutputFormat::Pdf`	✅ Full	Vector PDF with embedded fonts and backgrounds

Try It Yourself

Clone and Build

git clone https://github.com/thomasmost/hyper-render
cd hyper-render
cargo build

Run the Example

cargo run --example simple

This generates output.png and output.pdf in the current directory.

Render Your Own HTML

# Create a test HTML file
echo '<html><body style="background: #667eea; color: white; padding: 40px; font-family: system-ui;"><h1>My Page</h1><p>Hello from hyper-render!</p></body></html>' > test.html

# Render to PNG
cargo run --example from_file -- test.html output.png

# Render to PDF
cargo run --example from_file -- test.html output.pdf

Run Tests

cargo test

Generate Documentation

cargo doc --open

Architecture

hyper-render composes several best-in-class Rust crates:

HTML String
    ↓
html5ever (HTML parsing)
    ↓
Stylo (CSS parsing & cascade - from Firefox)
    ↓
Taffy (Flexbox/Grid layout)
    ↓
Blitz (DOM + rendering coordination)
    ↓
┌─────────────────┬─────────────────┐
│   Vello CPU     │     Krilla      │
│  (rasterizer)   │  (PDF writer)   │
└────────┬────────┴────────┬────────┘
         ↓                 ↓
       PNG               PDF

Performance

Benchmarks

Run benchmarks locally:

# Full benchmark suite
cargo bench --all-features

# Specific benchmark group
cargo bench full_pipeline

# Generate HTML reports
cargo bench --all-features  # Reports saved to target/criterion/

Sample Results (M1 MacBook Pro)

Benchmark	Time
PNG render (small HTML)	~10 ms
PNG render (medium HTML)	~13 ms
PNG render (large HTML, 50 items)	~13 ms
PDF render (small HTML)	~9 ms
PDF render (medium HTML)	~9 ms
PDF render (large HTML, 50 items)	~12 ms

Scaling impact (800x600 base):

Scale	Time	Pixels
1x	~13 ms	480K
2x	~21 ms	1.9M
3x	~32 ms	4.3M

Dimension impact:

Size	Time	Throughput
400x300	~11 ms	10M px/s
800x600	~13 ms	35M px/s
1920x1080	~18 ms	115M px/s

Build Size

Features	Library Size
none	250 KB
png	544 KB
pdf	513 KB
png,pdf (default)	767 KB

Check detailed size breakdown:

cargo install cargo-bloat
cargo bloat --release --all-features -n 20

Performance Characteristics

PNG rendering scales with pixel count: O(width × height × scale²)
PDF rendering scales with DOM complexity: O(nodes × text_length)
HTML parsing is generally fast; layout (Stylo/Taffy) dominates small documents
Font caching in PDF reduces repeated text rendering overhead

Known Issues

HTML Parser Warnings

You may see ERROR: Unexpected token messages when rendering HTML with non-standard CSS properties (e.g., mso-font-alt for Microsoft Office). These warnings come from the HTML parser and do not affect rendering — the output is still generated correctly.

To suppress these warnings, redirect stderr:

cargo run --example from_file -- input.html output.png 2>/dev/null

Limitations

JavaScript — Not supported (by design)
Web fonts — System fonts only; @font-face not yet supported
Images — External image loading not yet implemented
Some CSS — Advanced features like position: sticky, complex transforms may not work

Dependencies

Core rendering stack:

Blitz — HTML/CSS rendering engine
Stylo — Firefox's CSS engine
Taffy — Flexbox/Grid layout
Vello — 2D graphics (CPU renderer)
Krilla — PDF generation

License

MIT OR Apache-2.0

hyper-render 0.2.2