Struct Engine

pub struct Engine {
    pub timeline: Vec<Scene>,
    pub timenow: usize,
}

Engine

The Engine struct represents the core state manager of the RPGX system.
It maintains a timeline of Scenes (like a stack of game states or world instances), enabling dynamic transitions and rewinds across gameplay moments.

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Fields

• timeline: Vec<Scene>
  A timeline of game scenes, ordered by when they were pushed into the engine.

• timenow: usize
  The current index in the timeline, representing the active scene.

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Methods

new(scene: Scene) -> Self

Creates a new engine with the given initial scene.
The engine starts with one scene on its timeline and the pointer set to it.

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get_active_scene(&self) -> Option<&Scene>

Returns an immutable reference to the currently active scene, or None if the timeline is empty.

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get_active_scene_mut(&mut self) -> Option<&mut Scene>

Returns a mutable reference to the currently active scene, allowing modifications like pawn movement.

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push_scene(&mut self, scene: Scene)

Adds a new scene to the end of the timeline and updates the active pointer to it.
Useful when switching maps, progressing story, or entering sub-areas.

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pop_scene(&mut self)

Removes the last scene from the timeline if there is more than one.
Also updates timenow to point to the new last scene.

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rollback_to(&mut self, index: usize)

Rolls back the timeline to a specified earlier index.
All scenes after the index are removed, and the pointer is updated.

No-op if the index is out of bounds.

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rewind_to(&mut self, index: usize) -> Result<(), &str>

Moves the current scene pointer to a past scene in the timeline without removing any entries.
Returns an error string if the index is invalid.

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get_scene_at(&self, index: usize) -> Option<&Scene>

Gets an immutable reference to a scene at a specific point in the timeline, useful for review or replay features.

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Notes

• The engine timeline is inspired by save-states or undo-redo systems.
• Scenes can be pushed/popped for forward progression or state rollback.
• Engine provides centralized control over which scene is currently active.

Fields

timeline: Vec<Scene>

Timeline of scene states over time.

timenow: usize

Current index in the timeline (pointer to active scene).

Implementations

impl Engine

pub fn new(scene: Scene) -> Self

Create a new engine starting with an initial scene.

pub fn get_active_scene(&self) -> Option<&Scene>

Get a reference to the currently active scene.

pub fn get_active_scene_mut(&mut self) -> Option<&mut Scene>

Get a mutable reference to the currently active scene.

pub fn push_scene(&mut self, scene: Scene)

Push a new scene to the timeline and move the pointer to it.

pub fn pop_scene(&mut self)

Pop the last scene from the timeline if there’s more than one. Updates timenow to point to the new last scene.

pub fn rollback_to(&mut self, index: usize)

Roll back the timeline to the specified index, truncating all scenes after it. Updates timenow accordingly.

pub fn rewind_to(&mut self, index: usize) -> Result<(), &'static str>

Rewind to a specific point in the timeline without truncating. Returns error if the index is out of range.

pub fn get_scene_at(&self, index: usize) -> Option<&Scene>

Get a reference to the scene at the specified index.

Trait Implementations

impl Clone for Engine

fn clone(&self) -> Engine

Returns a duplicate of the value.

const fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.