How to run a shader from Shadertoy in your J/s file with WebGL and GLSL?

Question

I'm new to programming shaders and I want to create a shader with WebGL and GLSL. To see how it really works, I want to test a shader from Shadertoy. But how do you take the code from Shadertoy and actually get to run it in a J/S file? Do you just need to copy the code from Shadertoy into the fragment shader, or what?

Answer 1

See the following very basic example. You can put the Shadertoy code in the mainImage function in the fragment shader:

(function loadscene() {    

var canvas, gl, vp_size, prog, bufObj = {}, mousepos = [0, 0];

function initScene() {

    canvas = document.getElementById( "ogl-canvas");
    gl = canvas.getContext( "experimental-webgl" );
    if ( !gl )
      return;

    canvas.addEventListener('mousemove', (e) => {
        mousepos = [e.clientX, e.clientY];
    });

    progDraw = gl.createProgram();
    for (let i = 0; i < 2; ++i) {
        let source = document.getElementById(i==0 ? "draw-shader-vs" : "draw-shader-fs").text;
        let shaderObj = gl.createShader(i==0 ? gl.VERTEX_SHADER : gl.FRAGMENT_SHADER);
        gl.shaderSource(shaderObj, source);
        gl.compileShader(shaderObj);
        let status = gl.getShaderParameter(shaderObj, gl.COMPILE_STATUS);
        if (!status) alert(gl.getShaderInfoLog(shaderObj));
        gl.attachShader(progDraw, shaderObj);
        gl.linkProgram(progDraw);
    }
    status = gl.getProgramParameter(progDraw, gl.LINK_STATUS);
    if ( !status ) alert(gl.getProgramInfoLog(progDraw));
    progDraw.inPos = gl.getAttribLocation(progDraw, "inPos");
    progDraw.iTime = gl.getUniformLocation(progDraw, "iTime");
    progDraw.iMouse = gl.getUniformLocation(progDraw, "iMouse");
    progDraw.iResolution = gl.getUniformLocation(progDraw, "iResolution");
    gl.useProgram(progDraw);

    var pos = [ -1, -1, 1, -1, 1, 1, -1, 1 ];
    var inx = [ 0, 1, 2, 0, 2, 3 ];
    bufObj.pos = gl.createBuffer();
    gl.bindBuffer( gl.ARRAY_BUFFER, bufObj.pos );
    gl.bufferData( gl.ARRAY_BUFFER, new Float32Array( pos ), gl.STATIC_DRAW );
    bufObj.inx = gl.createBuffer();
    bufObj.inx.len = inx.length;
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, bufObj.inx );
    gl.bufferData( gl.ELEMENT_ARRAY_BUFFER, new Uint16Array( inx ), gl.STATIC_DRAW );
    gl.enableVertexAttribArray( progDraw.inPos );
    gl.vertexAttribPointer( progDraw.inPos, 2, gl.FLOAT, false, 0, 0 ); 
    
    gl.enable( gl.DEPTH_TEST );
    gl.clearColor( 0.0, 0.0, 0.0, 1.0 );

    window.onresize = resize;
    resize();
    requestAnimationFrame(render);
}

function resize() {
    //vp_size = [gl.drawingBufferWidth, gl.drawingBufferHeight];
    vp_size = [window.innerWidth, window.innerHeight];
    //vp_size = [256, 256]
    canvas.width = vp_size[0];
    canvas.height = vp_size[1];
}

function render(deltaMS) {

    gl.viewport( 0, 0, canvas.width, canvas.height );
    gl.clear( gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT );
   
    gl.uniform1f(progDraw.iTime, deltaMS/1000.0);
    gl.uniform2f(progDraw.iResolution, canvas.width, canvas.height);
    gl.uniform2f(progDraw.iMouse, mousepos[0], mousepos[1]);
    gl.drawElements( gl.TRIANGLES, bufObj.inx.len, gl.UNSIGNED_SHORT, 0 );
    
    requestAnimationFrame(render);
}  

initScene();

})();

<script id="draw-shader-fs" type="x-shader/x-fragment">
precision mediump float;

uniform vec2 iResolution;
uniform vec2 iMouse;
uniform float iTime;

void mainImage(out vec4 fragColor, in vec2 fragCoord)
{
    vec2 st = fragCoord.xy / iResolution.xy;
    fragColor = vec4(st, 0.0, 1.0);
}

void main() 
{
    mainImage( gl_FragColor, gl_FragCoord.xy );
}
</script>

<script id="draw-shader-vs" type="x-shader/x-vertex">
attribute vec2 inPos;

void main() 
{
    gl_Position = vec4(inPos, 0.0, 1.0);
}
</script>

<canvas id="ogl-canvas" style="border: none"></canvas>