Tresjs/docs/api/composables.md

Composables

Vue 3 Composition API allows you to create reusable logic that can be shared across components. It also allows you to create custom hooks that can be used in your components.

TresJS takes huge advantage of this API to create a set of composable functions that can be used to create animations, interact with the scene, and more. It also allows you to create more complex scenes that might not be possible using just the Vue Components (Textures, Loaders, etc.).

The core of TresJS uses these composables internally, so you would be using the same API that the core uses. For instance, components that need to updated on the internal render loop use the useRenderLoop composable to register a callback that will be called every time the renderer updates the scene.

useRenderLoop

The useRenderLoop composable is the core of TresJS animations. It allows you to register a callback that will be called on native refresh rate. This is the most important composable in TresJS.

const { onLoop, resume } = useRenderLoop()

onLoop(({ delta, elapsed }) => {
  // I will run at every frame ~ 60FPS (depending of your monitor)
})

::: warning Be mindfull of the performance implications of using this composable. It will run at every frame, so if you have a lot of logic in your callback, it might impact the performance of your app. Specially if you are updating reactive states or references. :::

The onLoop callback receives an object with the following properties based on the THREE clock:

• delta: The delta time between the current and the last frame. This is the time in seconds since the last frame.
• elapsed: The elapsed time since the start of the render loop.

This composable is based on useRafFn from vueuse. Thanks to @wheatjs for the amazing contribution.

Before and after render

You can also register a callback that will be called before and after the renderer updates the scene. This is useful if you add a profiler to measure the FPS for example.

const { onBeforeLoop, onAfterLoop } = useRenderLoop()

onBeforeLoop(({ delta, elapsed }) => {
  // I will run before the renderer updates the scene
  fps.begin()
})

onAfterLoop(({ delta, elapsed }) => {
  // I will run after the renderer updates the scene
  fps.end()
})

Pause and resume

You can pause and resume the render loop using the exposed pause and resume methods.

const { pause, resume } = useRenderLoop()

// Pause the render loop
pause()

// Resume the render loop
resume()

Also you can get the active state of the render loop using the isActive property.

const { resume, isActive } = useRenderLoop()

console.log(isActive) // false

resume()

console.log(isActive) // true

useLoader

The useLoader composable allows you to load assets using the THREE.js loaders. It returns a promise with loaded asset.

import { GLTFLoader } from 'three/examples/jsm/loaders/GLTFLoader'

const { scene } = await useLoader(THREE.GLTFLoader, 'path/to/asset.gltf')

Since the useLoader composable returns a promise, you can use it with async/await or then/catch. If you are using it on a component make sure you wrap it with a Suspense component. See Suspense for more information.

<template>
  <Suspense>
    <TheComponentUsingLoader />
  </Suspense>
</template>