hydra-rust

A Rust port of Hydra — the live-codable video synthesizer created by Olivia Jack. Takes Rhai scripts, compiles them to GLSL shaders, and renders them via OpenGL. The core is a library with zero GUI dependencies, suitable for embedding. A standalone binary is included for testing and standalone use. Originally extracted from Sova, the polyglot live coding sequencer.

Features

48 built-in functions

Category	Functions
Sources	osc, noise, voronoi, shape, gradient, solid, rings, checker
Geometry	rotate, scale, scroll, kaleid, pixelate, repeat, scrollX, scrollY, repeatX, repeatY, polar, cart, fold
Color	color, invert, contrast, brightness, saturate, hue, posterize, luma, colorama, shift, thresh, r, g, b
Blend	add, mult, blend, diff, layer, mask, sub
Modulate	modulate, modulateScale, modulateRotate, modulateRepeat, modulateRepeatX, modulateRepeatY, modulateKaleid, modulateScrollX, modulateScrollY, modulatePixelate, modulateHue
Other	text, src, initCam, fast, smooth, out, render, hush

Rendering

• 4-buffer ping-pong architecture (o0–o3)
• 4 external source slots (s0–s3) for webcam feeds
• Text rendering via bundled Hack font
• GLSL 330 (OpenGL 3.3 core profile)

Standalone binary

• Transparent editor overlay over GL visuals
• Syntax highlighting (OneDark theme)
• File save/load (.hydra files)
• Session persistence
• Options sidebar (tempo, font size, text opacity)
• Toggle editor visibility with Tab or Ctrl+Shift+H

Library

• Zero GUI dependencies — only rhai, glow, and ab_glyph
• Public API: eval(code) → Result<EvalResult, String>
• ShaderRenderer for OpenGL multipass rendering
• SourceManager for webcam capture (4 slots)

Build

cargo build          # library only
cargo run            # standalone binary
cargo test           # tests
cargo clippy         # lint

Example

osc(60.0, 0.1, time * 0.5)
  .kaleid(4.0)
  .color(1.0, 0.5, 0.3)
  .modulate(noise(3.0, 0.1), 0.02)
  .rotate(0.0, 0.1)
  .out()

Built-in globals available as GLSL expressions: time, beat, tempo, phase, mouseX, mouseY.

Used in Sova

hydra-rust is the visual engine of Sova, a polyglot live coding sequencer for music and visuals. In Sova, hydra shaders sync to the musical clock via beat, tempo, and phase, and can be shared across peers in multiplayer sessions.

Differences from browser Hydra

• Rhai, not JavaScript. No closures or arrow functions. Write osc(60.0, sin(time)) directly.
• Expression variables. time, beat, tempo, phase are GLSL uniform references, not callback functions.
• Mouse input. mouseX and mouseY are normalized to [0, 1].
• No speed global. Animation speed is per-source, controlled through function arguments.
• GLSL 330. Targets OpenGL 3.3 core profile.

Current limitations

• No video or image source loading
• No audio reactivity (FFT)
• Max nesting depth of 16

License

AGPL-3.0-or-later