# Instances

The core idea of **Tres** is an _autogenerated catalogue_ of all the ThreeJS elements. This catalogue is generated from the ThreeJS source code, so it's always up to date.

When using ThreeJS, you need to import the elements you want to use. For example, if you want to use a `PerspectiveCamera`, you need to import it from the `three` package:

```js
import { PerspectiveCamera } from 'three'

const camera = new PerspectiveCamera(45, width / height, 1, 1000)
```

With **Tres** you don't need to import anything, that's because **Tres** automatically generate a **Vue Component based of the Three Object you want to use in CamelCase with a Tres prefix**. For example, if you want to use a `PerspectiveCamera` you would use `<TresPerspectiveCamera />` component.

```vue
<template>
  <TresCanvas>
    <TresPerspectiveCamera />
    <!-- Your scene goes here -->
  </TresCanvas>
</template>
```

## Declaring objects

If we follow this argument, you should be able to lay out an instance like this: ❌

```vue
<template>
  <TresCanvas>
    <TresPerspectiveCamera visible :position="new THREE.Vector3(1, 2, 3)" />
    <!-- Your scene goes here -->
  </TresCanvas>
</template>
```

But with **Tres** this is not needed, you can define properties declaratively like this: ✅

```vue
<template>
  <TresCanvas>
    <TresPerspectiveCamera visible :position="[1, 2, 3]" />
    <!-- Your scene goes here -->
  </TresCanvas>
</template>
```

## Arguments

Some ThreeJS objects have arguments, for example, the `PerspectiveCamera` constructor has the following arguments:

- `fov` - Camera frustum vertical field of view.
- `aspect` - Camera frustum aspect ratio.
- `near` - Camera frustum near plane.
- `far` - Camera frustum far plane.

To pass these arguments to the `TresPerspectiveCamera` component, you can use the `args` prop:

```vue
<template>
  <TresCanvas>
    <TresPerspectiveCamera :args="[45, 1, 0.1, 1000]" />
    <!-- Your scene goes here -->
  </TresCanvas>
</template>
```

This is the same as doing this:

```ts
const camera = new PerspectiveCamera(45, 1, 0.1, 1000)
```