Creating a scene

The goal of this section is to give a brief introduction to glre.js. We will start by setting up a scene, with a spinning cube.

Before we started

Before you can use glre.js, you need somewhere to display it. Save the following HTML to a file on your computer.

<canvas id="myCanvas"></canvas>
<script type="module">
        import createGL from 'https://esm.sh/glre'

        // Our GLSL and Javascript will go here.
        const frag = `
                // ...
        `

        function App() {
                // ...
        }

        document.addEventListener('DOMContentLoaded', App)
</script>

Creating Fragment Shader

#version 300 es
precision highp float;
uniform vec2 iResolution; // canvas size
uniform vec3 up;          // camera up direction
uniform vec3 eye;         // camera position
uniform vec3 focus;       // camera focus point
uniform float focal;      // camera focal length
uniform float size;       // object size

Creating Box

float boxSDF(vec3 p, float side) {
        vec3 d = abs(p) - side;
        return min(max(d.x, max(d.y, d.z)), 0.) + length(max(d, 0.));
}

Raymarch Setup

• Calculate this particular pixel's normalized coordinates
• Calculate the direction that the ray through this pixel goes
• Calculate eye directions

void main() {
        /**
         * Ray marching setup
         */
        vec3 look = normalize(focus - eye);
        vec3 right = normalize(cross(look, up));
        vec2 scr = gl_FragCoord.xy - iResolution * .5;
        vec3 dir = normalize(focal * look + scr.x * right + scr.y * up);
        /**
        * Ray marching
        */
        vec3 p = eye + dir;
        vec3 e = vec3(.0005, .0, .0);
        float d = boxSDF(p, size);
        for (int i = 0; i < 50; i++) {
                if (d <= e.x) {
                        float dx = boxSDF(p + e.xyy, size) - d;
                        float dy = boxSDF(p + e.yxx, size) - d;
                        float dz = boxSDF(p + e.yyx, size) - d;
                        vec3 norm = normalize(vec3(dx, dy, dz));
                        fragColor = vec4(norm * .5 + .5, 1.);
                        return;
                }
                p = p + d * dir;
                d = boxSDF(p, size);
        }
}

Setup glre

function App() {
        const { mount, size, uniform } = createGL({
                el: document.getElementById('canvas'),
                frag,
                isWebGL: true,
                render() {
                        const t = performance.now() / 1000
                        const x = 200 * Math.cos(t)
                        const z = 200 * Math.sin(t)
                        uniform({ eye: [x, 0, z] })
                },
        })
        mount()
        uniform({
                up: [0, 1, 0],
                focus: [0, 0, 0],
                focal: 500,
                size: 50,
        })
}

document.addEventListener('DOMContentLoaded', App)

The result

<canvas id="id" style="top: 0; left: 0; position: fixed" />
<script type="module">
        import createGL from 'https://esm.sh/glre'

        const frag = `
                #version 300 es
                precision highp float;
                uniform vec2 iResolution; // canvas size
                uniform vec3 up;          // camera up direction
                uniform vec3 eye;         // camera position
                uniform vec3 focus;       // camera focus point
                uniform float focal;      // camera focal length
                uniform float size;       // object size
                out vec4 fragColor;
                /**
                 * boxSDF
                 */
                float boxSDF(vec3 p, float side) {
                        vec3 d = abs(p) - side;
                        return min(max(d.x, max(d.y, d.z)), 0.) + length(max(d, 0.));
                }
                /**
                 * main
                 */
                void main() {
                        /**
                         * Ray marching setup
                         */
                        vec3 look = normalize(focus - eye);
                        vec3 right = normalize(cross(look, up));
                        vec2 scr = gl_FragCoord.xy - iResolution * .5;
                        vec3 dir = normalize(focal * look + scr.x * right + scr.y * up);
                        /**
                         * Ray marching
                         */
                        vec3 p = eye + dir;
                        vec3 e = vec3(.0005, 0., 0.);
                        float d = boxSDF(p, size);
                        for (int i = 0; i < 50; i++) {
                                if (d <= e.x) {
                                        float dx = boxSDF(p + e.xyy, size) - d;
                                        float dy = boxSDF(p + e.yxx, size) - d;
                                        float dz = boxSDF(p + e.yyx, size) - d;
                                        vec3 norm = normalize(vec3(dx, dy, dz));
                                        fragColor = vec4(norm * .5 + .5, 1.);
                                        return;
                                }
                                p = p + d * dir;
                                d = boxSDF(p, size);
                        }
                }
        `

        export function App() {
                const { mount, size, uniform } = createGL({
                        el: document.getElementById('canvas'),
                        frag,
                        isWebGL: true,
                        render() {
                                const t = performance.now() / 1000
                                const x = 200 * Math.cos(t)
                                const z = 200 * Math.sin(t)
                                uniform({ eye: [x, 0, z] })
                        },
                })
                mount()
                uniform({
                        up: [0, 1, 0],
                        focus: [0, 0, 0],
                        focal: 500,
                        size: 50,
                })
        }

        document.addEventListener('DOMContentLoaded', App)
</script>