Quick Start

A complete program: open a window, run an event loop, and draw an animated frame.

A window and a frame loop

import io.github.edadma.sdl3.*

@main def main(): Unit =
  setMainReady()
  if !init(INIT_VIDEO) then
    System.err.println(s"SDL_Init failed: $error")
    return

  val window = createWindow("sdl3 quick start", 640, 480)
  if window.isNull then
    System.err.println(s"createWindow failed: $error")
    return

  val renderer = window.createRenderer()
  renderer.setVSync(true) // throttle the loop to the display refresh

  var running = true
  while running do
    // Drain the event queue each frame.
    var e = pollEvent()
    while e.isDefined do
      val ev = e.get
      if ev.kind == QUIT then running = false
      e = pollEvent()

    // Clear, draw, present.
    renderer.clear(Color(24, 24, 28))
    renderer.setDrawColor(Color(247, 103, 7))
    renderer.fillRect(270, 190, 100, 100)
    renderer.fillCircle(320, 240, 40, Color(255, 255, 255))
    renderer.present()

  renderer.destroy()
  window.destroy()
  quit()

Build and run it with sbt run (it blocks on the window). sbt nativeLink just produces the binary.

Reading input

Poll discrete events from the queue, or read the live device state at any time:

// Event-driven: react to a key press as it happens.
val ev = pollEvent().get
if ev.kind == KEY_DOWN && ev.keyScancode == Scancode.Escape then running = false

// State-driven: query held keys / the mouse each frame.
val keys = Keyboard.state
if keys(Scancode.Space) then jump()

val mouse = Mouse.state
if mouse.left then paint(mouse.x, mouse.y)

Adding text

Bring in sdl3_ttf to draw a label. Initialise it alongside SDL, open a font once, and blit rendered text as a texture:

import io.github.edadma.sdl3.*
import io.github.edadma.sdl3_ttf.*

ttfInit()
val font = openFont("/System/Library/Fonts/Helvetica.ttc", 24)

// each frame, after clear:
val tex = font.texture(renderer, "Hello, SDL3", Color(241, 243, 245))
renderer.copy(tex, 20, 20)
tex.destroy()

// at shutdown:
font.close()
ttfQuit()

For real apps, cache the text texture instead of rebuilding it every frame. See the modules section for each library’s full surface.