# Defining a new solid

A {class}`Solid` is defined as a {class}`Shape` and a {class}`Material` (and eventually a {class}`PTMaterial` for the path tracer). 
Its role is simply to wrap these data and pass them to the shader (with a proper ID).

To simplify the creation of scenes, it can be useful to build various extension of the {class}`Solid` class, that will
serve as shortcut to define a solid with a specific shape.

## Class extension

Every solid should extend the class {class}`Solid`. 
Note that {class}`Solid` inherits from {class}`Generic`, which defines methods various method to assign a UUID, a name, a scene ID, to the solid.


The constructor of {class}`Solid` takes the following arguments

- **shape** ({class}`Shape`) : a shape
- **material** ({class}`Material`) : a material (for basic rendering)
- **ptMaterial** ({class}`PTMaterial`) *optional* : a material for path tracing

## Properties and methods

The definition of a solid class does not require any particular property/method. All is already taken care of by the
class {class}`Generic` from which it inherits.

## Example

Below is the code used for euclidean balls.

```javascript
import {Solid} from "../../../core/solids/Solid.js";
import {BallShape} from "../shapes/ball/BallShape.js";

/**
 * @class
 *
 * @classdesc
 * Euclidean ball
 */
export class Ball extends Solid {

    /**
     * @param {Isometry|Point} location - the location of the ball
     * @param {number} radius - the radius of the ball
     * @param {Material} material - the material of the ball
     * @param {PTMaterial} ptMaterial - material for path tracing (optional)
     */
    constructor(location, radius, material, ptMaterial = undefined) {
        const shape = new BallShape(location, radius);
        super(shape, material, ptMaterial);
    }
}

```