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64 lines
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<title>on enter / on exit — Ludic</title>
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<meta name="description" content="Scene lifecycle hooks that fire as a scene becomes active or is left.">
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<header class="nav"><div class="wrap nav-in"><a class="brand" href="index.html"><span class="logo">L</span> Ludic</a><button class="nav-toggle" aria-label="Toggle menu" aria-expanded="false">☰</button><nav class="nav-links"><a href="index.html">Home</a><a href="api.html">API Reference</a><a class="nav-cta" href="https://git.workshopsoft.io/workshopsoft/ludic">Source ↗</a></nav></div></header>
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<main class="wrap item">
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<div class="crumbs"><a href="api.html">API Reference</a> <span>›</span> <a href="api.html#scenes">Scenes & layers</a> <span>›</span> <span class="here">on enter / on exit</span></div>
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<div class="item-head">
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<span class="kind-badge kind-keyword">keyword</span>
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<h1 id="top">on enter / on exit</h1>
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</div>
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<code class="sig">on enter { … } on exit { … }</code>
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<div class="desc"><p><code>on</code> introduces a scene's lifecycle hooks: <code>on enter { … }</code> runs once when the scene becomes active, and <code>on exit { … }</code> runs once as it is left. They are hooks, <b>not phases</b> — the place for per-scene setup and teardown that has no equivalent in a mode register. The start scene's <code>on enter</code> fires at boot right after the <code>Start</code> phase; on a <code>become Other</code> the current scene's <code>on exit</code> runs, the active scene switches, then the new scene's <code>on enter</code> runs. Use <code>on enter</code> to spawn the models a scene needs and reset its counters, and <code>on exit</code> to tidy up before leaving.</p></div>
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<div class="examples"><h2>Example</h2><pre data-lang="ludic">program SceneHookExample {
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property Position { column: int = 0, row: int = 0 }
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model Enemy { Position }
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var elapsed_frames: int = 0
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scene Overworld start {
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layer World {
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handler EnterBattle phase Update {
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if Input.key() == 'b' { become Battle }
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}
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handler DrawWorld phase Render {
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Screen.clear(Color.MidnightBlue)
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Screen.show()
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}
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}
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}
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scene Battle {
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on enter {
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elapsed_frames = 0
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spawn Enemy { Position { column: 8, row: 4 } }
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}
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on exit {
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for (any_position) in query [Position, {Enemy}] { despawn self() }
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}
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layer Fight {
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handler DrawBattle phase Render {
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Screen.clear(Color.Crimson)
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for (current_position) in query [Position, {Enemy}] {
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Screen.fill_rectangle(x: current_position.column * 16, y: current_position.row * 16, width: 16, height: 16, color: Color.White)
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}
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Screen.show()
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}
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}
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}
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}</pre></div>
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<a class="back" href="api.html">← All symbols</a>
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</main>
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<script src="ludic-highlight.js"></script>
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<script>Ludic.highlightAll(); Ludic.installCards(); Ludic.flashTarget();</script>
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