Source: \core\renderers\webgl\utils\Quad.js

    import glCore from 'pixi-gl-core';
import createIndicesForQuads from '../../../utils/createIndicesForQuads';

/**
 * Helper class to create a quad
 *
 * @class
 * @memberof PIXI
 */
export default class Quad
{
    /**
     * @param {WebGLRenderingContext} gl - The gl context for this quad to use.
     * @param {object} state - TODO: Description
     */
    constructor(gl, state)
    {
        /*
         * the current WebGL drawing context
         *
         * @member {WebGLRenderingContext}
         */
        this.gl = gl;

        /**
         * An array of vertices
         *
         * @member {Float32Array}
         */
        this.vertices = new Float32Array([
            -1, -1,
            1, -1,
            1, 1,
            -1, 1,
        ]);

        /**
         * The Uvs of the quad
         *
         * @member {Float32Array}
         */
        this.uvs = new Float32Array([
            0, 0,
            1, 0,
            1, 1,
            0, 1,
        ]);

        this.interleaved = new Float32Array(8 * 2);

        for (let i = 0; i < 4; i++)
        {
            this.interleaved[i * 4] = this.vertices[(i * 2)];
            this.interleaved[(i * 4) + 1] = this.vertices[(i * 2) + 1];
            this.interleaved[(i * 4) + 2] = this.uvs[i * 2];
            this.interleaved[(i * 4) + 3] = this.uvs[(i * 2) + 1];
        }

        /*
         * @member {Uint16Array} An array containing the indices of the vertices
         */
        this.indices = createIndicesForQuads(1);

        /*
         * @member {glCore.GLBuffer} The vertex buffer
         */
        this.vertexBuffer = glCore.GLBuffer.createVertexBuffer(gl, this.interleaved, gl.STATIC_DRAW);

        /*
         * @member {glCore.GLBuffer} The index buffer
         */
        this.indexBuffer = glCore.GLBuffer.createIndexBuffer(gl, this.indices, gl.STATIC_DRAW);

        /*
         * @member {glCore.VertexArrayObject} The index buffer
         */
        this.vao = new glCore.VertexArrayObject(gl, state);
    }

    /**
     * Initialises the vaos and uses the shader.
     *
     * @param {PIXI.Shader} shader - the shader to use
     */
    initVao(shader)
    {
        this.vao.clear()
        .addIndex(this.indexBuffer)
        .addAttribute(this.vertexBuffer, shader.attributes.aVertexPosition, this.gl.FLOAT, false, 4 * 4, 0)
        .addAttribute(this.vertexBuffer, shader.attributes.aTextureCoord, this.gl.FLOAT, false, 4 * 4, 2 * 4);
    }

    /**
     * Maps two Rectangle to the quad.
     *
     * @param {PIXI.Rectangle} targetTextureFrame - the first rectangle
     * @param {PIXI.Rectangle} destinationFrame - the second rectangle
     * @return {PIXI.Quad} Returns itself.
     */
    map(targetTextureFrame, destinationFrame)
    {
        let x = 0; // destinationFrame.x / targetTextureFrame.width;
        let y = 0; // destinationFrame.y / targetTextureFrame.height;

        this.uvs[0] = x;
        this.uvs[1] = y;

        this.uvs[2] = x + (destinationFrame.width / targetTextureFrame.width);
        this.uvs[3] = y;

        this.uvs[4] = x + (destinationFrame.width / targetTextureFrame.width);
        this.uvs[5] = y + (destinationFrame.height / targetTextureFrame.height);

        this.uvs[6] = x;
        this.uvs[7] = y + (destinationFrame.height / targetTextureFrame.height);

        x = destinationFrame.x;
        y = destinationFrame.y;

        this.vertices[0] = x;
        this.vertices[1] = y;

        this.vertices[2] = x + destinationFrame.width;
        this.vertices[3] = y;

        this.vertices[4] = x + destinationFrame.width;
        this.vertices[5] = y + destinationFrame.height;

        this.vertices[6] = x;
        this.vertices[7] = y + destinationFrame.height;

        return this;
    }

    /**
     * Binds the buffer and uploads the data
     *
     * @return {PIXI.Quad} Returns itself.
     */
    upload()
    {
        for (let i = 0; i < 4; i++)
        {
            this.interleaved[i * 4] = this.vertices[(i * 2)];
            this.interleaved[(i * 4) + 1] = this.vertices[(i * 2) + 1];
            this.interleaved[(i * 4) + 2] = this.uvs[i * 2];
            this.interleaved[(i * 4) + 3] = this.uvs[(i * 2) + 1];
        }

        this.vertexBuffer.upload(this.interleaved);

        return this;
    }

    /**
     * Removes this quad from WebGL
     */
    destroy()
    {
        const gl = this.gl;

        gl.deleteBuffer(this.vertexBuffer);
        gl.deleteBuffer(this.indexBuffer);
    }
}