tryst-sdl

SDL3 rendering, audio and gamepad input for tryst, Crystal's Tcl/Tk binding.

Rendering

Tryst::SDL::Viewport puts an SDL3 rendering surface inside a Tk window — a frame in the widget tree that SDL paints into instead of Tk:

require "tryst-sdl"

app = Tryst::App.new(title: "triangles")
app.show

viewport = Tryst::SDL::Viewport.new(app, width: 400, height: 400)

viewport.render do |target|
  target.clear(Tryst::SDL::Color::BLACK)
  target.draw_geometry([
    Tryst::SDL::Vertex.new(Tryst::SDL::Point.new(200, 40), Tryst::SDL::Color.new(255, 0, 0)),
    Tryst::SDL::Vertex.new(Tryst::SDL::Point.new(360, 360), Tryst::SDL::Color.new(0, 255, 0)),
    Tryst::SDL::Vertex.new(Tryst::SDL::Point.new(40, 360), Tryst::SDL::Color.new(0, 0, 255)),
  ])
end

app.mainloop

The renderer draws rects, lines, textures and arbitrary vertex geometry, with optional vsync. Textures load from image files (SDL3_image) and render from text (SDL3_ttf fonts). Keyboard input for a viewport comes through Tk bindings on the frame, not SDL's event loop — see Viewport#key_down?.

macOS caveat: on Aqua, Tk gives a native window to a toplevel but not to the frames inside it, so SDL is handed the whole toplevel and the surface covers every other widget in it (#covers_toplevel? reports this at runtime). A viewport that should share a screen with Tk widgets needs its own toplevel on macOS; on X11 it embeds in place. Viewport also sequences initialisation for you — SDL video must come up after Tk, never before, or the process aborts on macOS before main appears to run.

Audio

Sound effects, streaming music, tags for grouping, gain, fades, capture of the mixed output to a WAV, and push-based PCM output for generated audio:

require "tryst-sdl"

click = Tryst::SDL::Sound.new("click.wav")
click.play             # overlaps freely
click.play(gain: 0.25) # quieter

music = Tryst::SDL::Music.new("theme.ogg")
music.gain = 0.4
music.play             # loops forever by default
music.fade_out(1500)

Gamepad

Tryst::SDL::Gamepad reads controller buttons, sticks and triggers, polled from the Tk event loop alongside everything else.

Requirements

Crystal >= 1.21.0, Tcl/Tk 8.6 (whatever tryst itself needs), and the four SDL3 development packages. The build asks pkg-config for them, so whichever way they are installed, pkg-config --exists sdl3 sdl3-mixer sdl3-image sdl3-ttf has to succeed.

brew install sdl3 sdl3_mixer sdl3_image sdl3_ttf

On Linux, note that libsdl3-mixer-dev is the one that lags: as of writing it is in Debian forky and sid, but not in trixie, Ubuntu 26.04 or Alpine edge, which carry core/image/ttf only.

If installing manually rather than through a package manager, pkg-config needs the lowercase, hyphenated names (sdl3-mixer), not the CMake-style SDL3_mixer.

Examples

Run these from this directory, not the repo root — Crystal resolves require "tryst" against the lib/ of wherever it runs, and only tryst-sdl/lib has tryst in it. From elsewhere they fail with can't find file 'tryst'.

cd tryst-sdl
crystal run examples/geometry.cr        # gradient triangles in a Tk window
crystal run examples/sound_effects.cr   # overlapping clips, per-play gain, tags
crystal run examples/music.cr           # loop, pause, seek, graceful end, fade out
crystal run examples/panning.cr         # hard pans, a sweep, and a 3D orbit
crystal run examples/capture.cr         # record the mix to a WAV
crystal run examples/theremin.cr        # Tk sliders driving generated audio
crystal run examples/yam/yam.cr         # minesweeper, with sound effects

The audio examples make sound — turn your volume up. geometry.cr, theremin.cr and yam.cr open a window and need a display; the rest are console only.

Tests

shards install
crystal spec                  # host
scripts/docker-test.sh        # Debian forky + Xvfb, same suite

Both run the same examples with nothing skipped or gated by platform. scripts/docker-test.sh builds from this repo's own root; shards install inside the image fetches tryst directly via its github: dependency. It takes the same arguments crystal spec does, so a focused run works there too.