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Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

            
              <!--

Flag in the wind, inspired by this "animate the air" tweet by artist Felix Colgrave (who made the amazing Double King short animation): https://mobile.twitter.com/FelixColgrave/status/858658886445711360

This code simulates a chain of air bubbles in 2D, and then wraps a virtual flag ribbon around them. That produces a reasonable approximation of "fluid dynamics" of air, which works well for a specific stylized look.

Libraries:

- PlanckJS (improved Box2D for physics simulation): http://piqnt.com/planck.js/
- onecolor (RGB conversion): https://github.com/One-com/one-color
- theme from https://color.adobe.com/Color-Theme-5-color-theme-11764289/
- visual style and technique by Felix Colgrave (https://mobile.twitter.com/FelixColgrave)

-->
            
          
!
            
              const onecolor = one.color;

class BannerWorld {
    constructor() {
        this._ballFD = {
            density : 1.0,
            friction : 0.6
        };

        this._world = new planck.World({
            gravity: planck.Vec2(0.1, 0)
        });

        this._ground = this._world.createBody();
        this._ground.createFixture(planck.Edge(planck.Vec2(-0.1, -50), planck.Vec2(-0.1, 50)), {
            density: 0,
            friction: 0.6
        });

        this._bodyList = [];
        this._startingDirection = 1;

        this._spawnCountdown = 0;
    }

    step(dt) {
        const world = this._world;
        const bodyList = this._bodyList;

        // spawn new bodies
        this._spawnCountdown -= dt;

        if (this._spawnCountdown < 0) {
            // check if spawn area is too crowded
            const readyForSpawn = bodyList.length === 0 || bodyList[bodyList.length - 1].getPosition().x - bodyList[bodyList.length - 1].data.radius > 0.6;

            if (readyForSpawn) {
                this._spawnCountdown += 0.4;

                const radius = 0.3;
                const body = world.createDynamicBody(planck.Vec2(radius, this._startingDirection * (-radius + Math.random() * 0.1)))
                const fixture = body.createFixture(planck.Circle(radius), this._ballFD);
                body.setLinearVelocity(planck.Vec2(1.2, this._startingDirection * (0.5 + Math.random() * 1.5)));

                body.data = {
                    prevJoint: null,
                    nextJoint: null,
                    sizeCountdown: 0,
                    radius: radius,
                    fixture: fixture
                };

                if (bodyList.length > 0) {
                    const prevBody = bodyList[bodyList.length - 1];

                    // @todo consider also a rotation joint to keep folds in the right order
                    prevBody.data.nextJoint = body.data.prevJoint = world.createJoint(planck.DistanceJoint({
                        collideConnected: true, // rigid minimum distance
                        frequencyHz: 0.2,
                        dampingRatio: 0.5,
                        bodyA: prevBody,
                        localAnchorA: planck.Vec2(0, 0),
                        bodyB: body,
                        localAnchorB: planck.Vec2(0, 0),
                        length: (prevBody.data.radius + radius) * 1.3
                    }));
                }

                bodyList.push(body);
                this._startingDirection = -this._startingDirection;
            } else {
                this._spawnCountdown += 0.1; // do another check soon
            }
        }

        // process each moving body
        bodyList.forEach((body, index) => {
            body.data.sizeCountdown -= dt;

            if (body.data.sizeCountdown < 0) {
                body.data.sizeCountdown += 0.1 + Math.random() * 0.3;

                const nextRadius = body.data.radius + (1.5 - body.data.radius) * Math.random() * 0.05;
                const nextFixture = body.createFixture(planck.Circle(nextRadius), this._ballFD);

                body.destroyFixture(body.data.fixture);

                body.data.fixture = nextFixture;
                body.data.radius = nextRadius;

                if (index > 0) {
                    const prevBody = bodyList[index - 1];
                    body.data.prevJoint.setLength((prevBody.data.radius + nextRadius) * 1.3);
                }

                if (index < bodyList.length - 1) {
                    const nextBody = bodyList[index + 1];
                    body.data.nextJoint.setLength((nextBody.data.radius + nextRadius) * 1.3);
                }
            }
        });

        // eliminate furthest offscreen bubble in the chain
        if (bodyList.length > 0) {
            const lastBody = bodyList[0];
            const position = lastBody.getPosition();

            if (position.x > 30) {
                world.destroyBody(lastBody);
                bodyList.splice(0, 1);
            }
        }
    }
}

const canvas = document.createElement('canvas');
canvas.style.position = 'absolute';
canvas.style.top = '0vh';
canvas.style.left = '0vw';
canvas.style.width = '100vw';
canvas.style.height = '100vh';
document.body.appendChild(canvas);

const bufferWidth = canvas.offsetWidth;
const bufferHeight = canvas.offsetHeight;
const aspectRatio = bufferWidth / bufferHeight;
canvas.width = bufferWidth;
canvas.height = bufferHeight;

const ctx = canvas.getContext('2d');

const main = new BannerWorld();

// pre-simulate to get some length going
// @todo spread out over a few frames
Array.apply(null, new Array(800)).forEach(() => {
    const dt = 1 / 60.0;
    main._world.step(dt);
    main.step(dt);
});

const pointXTmp = [];
const pointYTmp = [];
const pointITmp = [];

function renderer() {
    const dt = 1 / 60.0;
    main._world.step(dt);
    main.step(dt);

    pointXTmp.length = 0;
    pointYTmp.length = 0;
    pointITmp.length = 0;

    const segmentTravel = 0.4;
    const segmentCount = 150;
    let segmentIndex = 0;

    let direction = -main._startingDirection; // first body gets the proper winding direction
    let bx = 0, by = 0, br = 0;
    let azimuth = 0;
    let travelLeft = 0;
    let nextBodyIndex = main._bodyList.length - 1;

    while (nextBodyIndex >= 0) {
        // determine arc and line segment towards next body
        const nextBody = main._bodyList[nextBodyIndex];
        const nextPos = nextBody.getPosition();
        const nextRadius = nextBody.data.radius - 0.15;

        const dx = nextPos.x - bx;
        const dy = nextPos.y - by;
        const nextBodyDirection = Math.atan2(dy, dx);

        const distance = Math.sqrt(dx * dx + dy * dy);
        const projectedDistance = Math.min(distance, br + nextRadius);
        const alongDistance = Math.sqrt(distance * distance - projectedDistance * projectedDistance);

        const alphaSine = projectedDistance / distance;
        const arcEndAzimuth = nextBodyDirection - direction * (Math.PI / 2 - Math.asin(alphaSine));

        // ensure end of arc is always "ahead" of the starting azimuth
        const arcAzimuthDelta = arcEndAzimuth - azimuth;
        const extraRotations = -Math.floor(direction * arcAzimuthDelta / (Math.PI * 2));
        const arcLength = direction * (arcAzimuthDelta + direction * extraRotations * Math.PI * 2) * br;

        const travelUntilStraightPortion = travelLeft + arcLength;
        const arcSegmentCount = Math.floor(travelUntilStraightPortion / segmentTravel);
        const displayedArcSegmentCount = Math.min(arcSegmentCount, segmentCount - segmentIndex);

        // step through arc segments, drawing line to end of each one (hence 1-based loop)
        for (let i = 1; i <= displayedArcSegmentCount; i += 1) {
            const segmentAzimuth = azimuth + direction * (i * segmentTravel - travelLeft) / br;
            pointXTmp.push(bx + Math.cos(segmentAzimuth) * br);
            pointYTmp.push(by + Math.sin(segmentAzimuth) * br);
            pointITmp.push(pointITmp.length);
        }

        segmentIndex += displayedArcSegmentCount;

        // step through the linear portion
        const travelLeftInArc = travelUntilStraightPortion - arcSegmentCount * segmentTravel;
        const travelUntilNextArc = travelLeftInArc + alongDistance;
        const straightSegmentCount = Math.floor(travelUntilNextArc / segmentTravel);
        const displayedStraightSegmentCount = Math.min(straightSegmentCount, segmentCount - segmentIndex);
        const endCos = Math.cos(arcEndAzimuth);
        const endSin = Math.sin(arcEndAzimuth);

        // draw to first segment point on the line
        if (displayedStraightSegmentCount > 0) {
            const firstSegmentLinearTravel = direction * (segmentTravel - travelLeftInArc);
            pointXTmp.push(bx + endCos * br - endSin * firstSegmentLinearTravel);
            pointYTmp.push(by + endSin * br + endCos * firstSegmentLinearTravel);
            pointITmp.push(pointITmp.length);
        }

        // draw to last segment point on the line
        if (displayedStraightSegmentCount > 1) {
            const lastSegmentLinearTravel = direction * (segmentTravel * displayedStraightSegmentCount - travelLeftInArc);
            pointXTmp.push(bx + endCos * br - endSin * lastSegmentLinearTravel);
            pointYTmp.push(by + endSin * br + endCos * lastSegmentLinearTravel);
            pointITmp.push(pointITmp.length);
        }

        segmentIndex += displayedStraightSegmentCount;

        bx = nextPos.x;
        by = nextPos.y;
        br = nextRadius;
        azimuth = arcEndAzimuth + Math.PI; // next arc starts at opposite side of circle
        travelLeft = travelUntilNextArc - straightSegmentCount * segmentTravel;
        direction = -direction;
        nextBodyIndex -= 1;
    }

    pointITmp.sort((a, b) => pointYTmp[b] - pointYTmp[a]);

    ctx.fillStyle = '#6FA8BF';
    ctx.fillRect(0, 0, bufferWidth, bufferHeight);

    const pigmentColor = onecolor('#D94A4A');

    ctx.save();

    ctx.translate(bufferWidth / 2, bufferHeight / 2);
    ctx.scale(bufferHeight / 15, -bufferHeight / 15);
    ctx.translate(-8, 1);

    ctx.lineWidth = 0.2;
    ctx.miterLimit = 2;
    ctx.strokeStyle = '#F2EAE4';

    // bottom outline behind the main fill
    ctx.beginPath();

    ctx.moveTo(0, -2);

    for (let i = 0; i < pointXTmp.length; i += 1) {
        const x = pointXTmp[i];
        const y = pointYTmp[i] * 0.5;
        ctx.lineTo(x, y - 2);
    }

    ctx.stroke();

    // main fill, sorted by depth
    for (let i = 0; i < pointITmp.length; i += 1) {
        const index = pointITmp[i];
        const lx = index === 0 ? 0 : pointXTmp[index - 1];
        const ly = (index === 0 ? 0 : pointYTmp[index - 1]) * 0.5;
        const x = pointXTmp[index];
        const y = pointYTmp[index] * 0.5;

        const dx = x - lx;
        const dy = y - ly;

        const bias = 0.01 * Math.sign(dx); // pixel bias to avoid visual gaps due to anti-alias

        ctx.fillStyle = dx < 0 ? '#3E3F59' : pigmentColor.lightness(-(1 - dx * dx / (dx * dx + dy * dy)) * 0.4, true).css();
        ctx.beginPath();

        ctx.moveTo(lx - bias, ly);
        ctx.lineTo(x + bias, y);
        ctx.lineTo(x + bias, y - 2);
        ctx.lineTo(lx - bias, ly - 2);

        ctx.fill();
    }

    // top outline above fill
    ctx.lineWidth = 0.1;
    ctx.beginPath();

    ctx.moveTo(0, -2);
    ctx.lineTo(0, 0);

    for (let i = 0; i < pointXTmp.length; i += 1) {
        const x = pointXTmp[i];
        const y = pointYTmp[i] * 0.5;
        ctx.lineTo(x, y);
    }

    ctx.stroke();

    // main._bodyList.forEach(body => {
    //     const pos = body.getPosition();
    //     ctx.fillStyle = '#0f0';
    //     ctx.fillRect(pos.x - 0.05, pos.y - 0.05, 0.1, 0.1);
    // });

    ctx.restore();

    window.requestAnimationFrame(renderer);
}

renderer();

// planck.testbed('Banner', function (testbed) {
//     testbed.step = function (dtms) {
//         const dt = dtms / 1000;

//         main.step(dt);
//     };

//     testbed.x = 0;
//     testbed.y = 0;
//     testbed.info('Banner animation');

//     return main._world;
// });

            
          
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