SummationByParts/main.js

import { Universe, set_panic_hook, default as init } from "./maxwell.js";

async function run() {
    let wasm = await init("./maxwell_bg.wasm");
    set_panic_hook();

    const canvas = document.getElementById("glCanvas");

    const gl = canvas.getContext("webgl");
    if (gl === null) {
        console.error("Unable to initialise WebGL");
        return;
    }

    const vsSource = String.raw`
        #version 100
        attribute mediump float aX;
        attribute mediump float aY;
        attribute mediump float aField;

        uniform vec4 uBbox;

        varying mediump float vField;

        void main() {
            vField = aField;
            mediump float x = (aX - uBbox.x)*uBbox.y;
            mediump float y = (aY - uBbox.z)*uBbox.w;
            gl_Position = vec4(2.0*x - 1.0, 2.0*y - 1.0, 1.0, 1.0);
        }
    `;

    const fsSource = String.raw`
        #version 100
        varying mediump float vField;

        uniform int uChosenField;

        void main() {
            mediump float r = 0.0;
            mediump float g = 0.0;
            mediump float b = 0.0;

            if (uChosenField == 0) {
                r = vField + 0.5;
            } else if (uChosenField == 1) {
                g = (vField + 1.0)/2.0;
            } else {
                b = vField + 0.5;
            }
            gl_FragColor = vec4(r, g, b, 1.0);
        }
    `;

    const vsShader = gl.createShader(gl.VERTEX_SHADER);
    gl.shaderSource(vsShader, vsSource);
    gl.compileShader(vsShader);
    if (!gl.getShaderParameter(vsShader, gl.COMPILE_STATUS)) {
        console.error('Could not compile shader: ' + gl.getShaderInfoLog(vsShader));
        return;
    }

    const fsShader = gl.createShader(gl.FRAGMENT_SHADER);
    gl.shaderSource(fsShader, fsSource);
    gl.compileShader(fsShader);
    if (!gl.getShaderParameter(fsShader, gl.COMPILE_STATUS)) {
        console.error('Could not compile shader: ' + gl.getShaderInfoLog(fsShader));
        return;
    }

    const shaderProgram = gl.createProgram();
    gl.attachShader(shaderProgram, vsShader);
    gl.attachShader(shaderProgram, fsShader);
    gl.linkProgram(shaderProgram);
    gl.validateProgram(shaderProgram);
    if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
        console.error('Unable to link shader program: ' + gl.getProgramInfoLog(shaderProgram))
        return;
    }
    gl.useProgram(shaderProgram);

    gl.clearColor(1.0, 0.753, 0.796, 1.0); // A nice pink to show missing values
    gl.clearDepth(1.0);
    gl.enable(gl.DEPTH_TEST);
    gl.depthFunc(gl.LEQUAL);
    gl.disable(gl.CULL_FACE);

    console.info("Successfully set OpenGL state");


    const width = 40;
    const height = 50;


    let x = new Float32Array(width*height);
    let y = new Float32Array(width*height);
    for (let j = 0; j < height; j++) {
        for (let i = 0; i < width; i++) {
            const n = width*j + i;
            x[n] = i / (width - 1.0);
            y[n] = j / (height - 1.0);
        }
    }

    const universe = new Universe(width, height);


    // Transfer x, y to cpu, prepare fBuffer
    const xBuffer = gl.createBuffer();
    const yBuffer = gl.createBuffer();
    const fBuffer = gl.createBuffer();
    {
        const numcomp = 1;
        const type = gl.FLOAT;
        const normalise = false;
        const stride = 0;
        const offset = 0;

        let loc = gl.getAttribLocation(shaderProgram, 'aX');
        gl.bindBuffer(gl.ARRAY_BUFFER, xBuffer);
        gl.vertexAttribPointer(loc, numcomp, type, normalise, stride, offset);
        gl.enableVertexAttribArray(loc);
        gl.bufferData(gl.ARRAY_BUFFER, x, gl.STATIC_DRAW);

        loc = gl.getAttribLocation(shaderProgram, 'aY');
        gl.bindBuffer(gl.ARRAY_BUFFER, yBuffer);
        gl.vertexAttribPointer(loc, numcomp, type, normalise, stride, offset);
        gl.enableVertexAttribArray(loc);
        gl.bufferData(gl.ARRAY_BUFFER, y, gl.STATIC_DRAW);

        loc = gl.getAttribLocation(shaderProgram, 'aField');
        gl.bindBuffer(gl.ARRAY_BUFFER, fBuffer);
        gl.enableVertexAttribArray(loc);
        gl.vertexAttribPointer(loc, numcomp, type, normalise, stride, offset);
    }

    // Create triangles covering the domain
    let positions = new Int16Array((width-1)*(height-1)*2*3);
    for (let j = 0; j < height - 1; j++) {
        for (let i = 0; i < width - 1; i++) {
            const n = 2*3*((width-1)*j + i);
            positions[n+0] = width*j + i;
            positions[n+1] = width*j + i+1;
            positions[n+2] = width*(j+1) + i;
            positions[n+3] = width*j + i+1;
            positions[n+4] = width*(j+1) + i;
            positions[n+5] = width*(j+1) + i+1;
        }
    }

    const indexBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indexBuffer);
    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, positions, gl.STATIC_DRAW);

    let bbox = [+Infinity, -Infinity, +Infinity, -Infinity];
    for (let i = 0; i < width*height; i++) {
        bbox[0] = Math.min(bbox[0], x[i]);
        bbox[1] = Math.max(bbox[1], x[i]);
        bbox[2] = Math.min(bbox[2], y[i]);
        bbox[3] = Math.max(bbox[3], y[i]);
    }

    {
        const loc = gl.getUniformLocation(shaderProgram, 'uBbox');
        gl.uniform4f(loc, bbox[0], 1.0/(bbox[1] - bbox[0]), bbox[2], 1.0/(bbox[3] - bbox[2]));
    }

    const TIMEFACTOR = 10000.0;
    const MAX_DT = 2.0/Math.max(width, height);

    let t = 0;
    let first_draw = true;
    let warn_time = -1;
    const chosenField = {
        uLocation: gl.getUniformLocation(shaderProgram, 'uChosenField'),
        value: 0,
        cycle: function() {
            if (this.value == 0) {
                this.value = 1;
            } else if (this.value == 1) {
                this.value = 2;
            } else {
                this.value = 0;
            }
            gl.uniform1i(this.uLocation, this.value);
        },
    };
    chosenField.cycle();

    universe.init(0.5, 0.5);

    function drawMe(t_draw) {
        gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

        let dt = (t_draw - t) / TIMEFACTOR;
        t = t_draw;
        if (first_draw || dt <= 0.0) {
            first_draw = false;
            dt = MAX_DT;
        } else {
            if (dt >= MAX_DT) {
                warn_time += 1;
                if (warn_time != -2) {
                    console.warn("Can not keep up with framerate");
                }
                dt = MAX_DT;
            }
        }
        universe.advance(dt/2);
        universe.advance(dt/2);

        let field_ptr;
        if (chosenField.value == 0) {
            field_ptr = universe.get_ex_ptr();
        } else if (chosenField.value == 1) {
            field_ptr = universe.get_hz_ptr();
        } else {
            field_ptr = universe.get_ey_ptr();
        }
        const field = new Float32Array(wasm.memory.buffer, field_ptr, width*height);
        gl.bufferData(gl.ARRAY_BUFFER, field, gl.DYNAMIC_DRAW);

        {
            const offset = 0;
            const type = gl.UNSIGNED_SHORT;
            const vertexCount = positions.length;
            gl.drawElements(gl.TRIANGLES, vertexCount, type, offset);
        }

        window.requestAnimationFrame(drawMe);
    }

    // https://stackoverflow.com/questions/4288253/html5-canvas-100-width-height-of-viewport#8486324
    function resizeCanvas() {
        canvas.width = window.innerWidth;
        canvas.height = window.innerHeight;

        gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight);
    }

    window.addEventListener('keyup', event => {
        if (event.key == 'c') {
            chosenField.cycle();
        }
    }, {passive: true});
    window.addEventListener('resize', resizeCanvas, false);
    window.addEventListener('click', event => {
        // Must adjust for bbox and transformations for x/y
        const mousex = event.clientX / window.innerWidth;
        const mousey = event.clientY / window.innerHeight;
        universe.init(mousex, 1.0 - mousey);
    }, {passive: true});

    resizeCanvas();
    window.requestAnimationFrame(drawMe);
}

run();