Scene changes

Scene changes: transitions, pause menus, loading screens

A game moves between scenes: from the title to the first level, from level to level, to a game over screen. This page covers how those changes look (transitions), opening a scene over another (a pause menu, an inventory, a dialog), and showing a loading screen while the next scene gets ready.

• Going to another scene
• Transitions: fades and wipes
• Scenes over scenes: pause menus
• Loading screens
• Scene changes in scripts
• How it’s stored
• Questions

Going to another scene

Three ways:

• A Button’s Action: Go to (scene).
• A Menu item’s action scene:Level1 (Menus made in scene files).
• A script: e.Game_ChangeScene(self.game, "Level1").

Every scene starts fresh each time it’s entered: its nodes are made again from its file, as they were when the game started.

Transitions: fades and wipes

Project Settings (File > Project Settings) > General > Scene change:

Kind	The screen
None	Changes at once
Fade	Fades to a color, then fades the new scene in
Wipe_Left, Wipe_Right, Wipe_Up, Wipe_Down	A color sweeps across from that side, then away
Circle	A circle closes on the middle, then opens on the new scene

Change time is the whole change in seconds (covering takes half, uncovering the other half); Change color the cover’s color. Every scene change by an action uses it; scripts can use another (below).

Scenes over scenes: pause menus

A pause menu is its own scene (with a Panel and Buttons: see the UI system) opened over the level: the level stays where it is, frozen, drawn under the menu.

1. Make a scene PauseMenu with a half-transparent Panel and buttons Resume and Quit to Title.
2. On Resume, set Action to Close this (back to the scene under it).
3. On Quit to Title, Go to Title.
4. Open it from the level: a Button whose action is Open PauseMenu over this, or a script when Escape is pressed:

Level_update :: proc(self: ^Level, events: []sdl.Event, dt: f64) {
  if e.Input_IsActionJustPressed("pause", self.game) do e.Game_PushScene(self.game, "PauseMenu")
}

While a scene is open over another, the one under it doesn’t update (its scripts, physics and animations wait) but is still drawn. For a HUD that runs alongside the level, open it with e.Game_PushScene(game, "Hud", pauseBelow = false): both update.

Going to another scene closes everything open over the old one.

Loading screens

Normally a game builds all its scenes when it starts. A big game can start faster, and show something while each level gets ready:

1. Make a scene Loading: a background, a “Loading…” text, and a ProgressBar with Shows loading ticked (it fills as the loading goes).
2. Project Settings > General > Loading scene: Loading.

Now the game builds only its start scene and the loading scene when it starts. Going to any other scene shows the loading scene (with the transition) while that scene’s images and sounds load, a few each frame, for at least half a second; then the scene is built and shown.

Scene changes in scripts

Code	What it does
e.Game_ChangeScene(game, "Level2")	Goes there with the project’s transition
e.Game_ChangeScene(game, "Level2", e.Transition{kind = .Fade, duration = 1, color = {255, 255, 255, 255}})	With another transition ({kind = .None}: at once)
e.Game_PushScene(game, "PauseMenu")	Opens a scene over the playing one (pauseBelow = false: both update)
e.Game_PopScene(game)	Closes the scene on top
e.Game_TopScene(game)	The scene on top
e.Game_IsChangingScene(game)	A transition is under way (ignore input meanwhile, say)
e.Game_LoadingProgress(game)	How far the loading screen has got, 0 to 1
e.Game_RunAction(game, "push:Shop")	Runs an action like a Button’s (scene:, push:, pop, quit)

A scene’s onEnter and onExit events (and globals’ sceneChanged) still come as the scene changes, under the cover.

How it’s stored

On project.xml’s root:

<project name="My Game" startScene="Title" transition="Fade" transitionTime="0.6" transitionColor="#000000ff" loadingScene="Loading">

Button actions: action="scene:Level1", action="push:PauseMenu", action="pop", action="quit"; a ProgressBar’s showLoading="true".

Questions

My pause menu’s buttons don’t react. Its scene needs the buttons, and the level must not take the same keys: the level waits while the menu is open (unless it was opened with pauseBelow = false).

The loading screen flashes by. It shows at least half a second; with a transition, plus the transition. Most scenes load quickly: that’s fine.

A script looks for a node in another scene and finds nothing. With a loading scene, scenes that haven’t been entered aren’t built yet. Look nodes up in the scene that’s playing.