[轉載] Create a Dynamic Point Mesh Animation with HTML5 Canvas Back

• Author: Dudley Storey
• Origin: http://thenewcode.com/1159/Create-a-Dynamic-Point-Mesh-Animation-with-HTML5-Canvas?utm_source=codropscollective
• Time: Nov, 22nd, 2016

See the Pen Dynamic Point Mesh Animation with HTML5 Canvas by aleen42 (@aleen42) on CodePen.

Perhaps one of the most recognizable visual motifs of the last several years is the animation style you should see above; I'm not sure it has a name, but I call it a dynamic point mesh animation. This is my variation on the style, derived from previous work by Daniel Mayovskiy.

Frequently such animations are layered behind other content, so it makes sense to size this example to the same size as the viewport:

<canvas id="canvas"></canvas>

The CSS:

body {
    background: #222;
    margin: 0rem;
    min-height: 100vh;
}

#canvas {
    position: absolute;
    display: block;
    top: 0;
    left: 0;
    z-index: -1;
}

The Codepen version of this code has a little more detail, including the CSS and markup for placing the text on top of the animation.

To ensure that the <canvas> is always the full height and width of the viewport, the first part of the JavaScript at the end of the page is a resize function:

let resizeReset = function () {
    w = canvasBody.width = window.innerWidth;
    h = canvasBody.height = window.innerHeight;
};

Creating the Dots

opts is an object that contains a series of properties that act as default values for the script:

const opts = { 
    particleColor: "rgb(200,200,200)",
    lineColor: "rgb(200,200,200)",
    particleAmount: 40,
    defaultSpeed: 1,
    variantSpeed: 1,
    defaultRadius: 2,
    variantRadius: 2,
    linkRadius: 200,
};

The variants for speed and radius are used to add randomness to the size and movement of the mesh points; linkRadius is how close the points must come before they are joined with lines.

The <canvas> element must be resized so that the particles always meet the edge of the browser window. The resizeReset() function is called once on script load, but needs to be throttled or "debounced" so that it doesn't slow down the script during operation of the rest of the page:

let delay = 200, tid;

window.addEventListener("resize", function () {
    deBouncer();
});

let deBouncer = function () {
    clearTimeout(tid);

    tid = setTimeout(function () {
        resizeReset();
    }, delay);
};

The Particle object is a fairly large function that generates each of the "dots":

Particle = function (xPos, yPos) { 
    this.x = Math.random() * w; 
    this.y = Math.random() * h;
    this.speed = opts.defaultSpeed + Math.random() * opts.variantSpeed; 
    this.directionAngle = Math.floor(Math.random() * 360); 
    this.color = opts.particleColor;
    this.radius = opts.defaultRadius + Math.random() * opts. variantRadius; 

    this.vector = {
        x: Math.cos(this.directionAngle) * this.speed,
        y: Math.sin(this.directionAngle) * this.speed
    };

    this.update = function () { 
        this.border(); 
        this.x += this.vector.x; 
        this.y += this.vector.y; 
    };

    this.border = function () { 
        if (this.x >= w || this.x <= 0) { 
            this.vector.x *= -1;
        }

        if (this.y >= h || this.y <= 0) {
            this.vector.y *= -1;
        }

        if (this.x > w) this.x = w;
        if (this.y > h) this.y = h;
        if (this.x < 0) this.x = 0;
        if (this.y < 0) this.y = 0; 
    };

    this.draw = function () { 
        drawArea.beginPath();
        drawArea.arc(this.x, this.y, this.radius, 0, Math.PI*2);
        drawArea.closePath();
        drawArea.fillStyle = this.color;
        drawArea.fill();
    };
};

In the context of the script, this refers to each particle, as it is created:

• the initial position, speed and angle of each particle are decided randomly; the particle's color is determined from the associated option setting.
• this.vector stores the direction of the particle: if this.vector.x is 1, it's moving to the right; if -1, it's moving to the left. Similarly, if this.vector.y is negative, it's moving up, if positive, it's moving down.
• this.update calculates the next coordinates for each particle. First, it checks if the particle is touching the border; if the particle goes past the dimensions of the canvas, it's vector is changed, multiplied by -1 to produce the opposite direction
• a window resize may leave a particle further across the perimeter than the border function will capture, so a series of if statements checks if that's the case, resetting the position of the particle to the current limits of the canvas.
• finally, the dots are drawn in place.

To start it all moving, we need the following:

function setup() { 
    particles = [];

    for (let i = 0; i < opts.particleAmount; i++){
        particles.push( new Particle() );
    }

    window.requestAnimationFrame(loop);
}

The setup function creates a particles array, and fills it with a series of particle elements before calling the loop function, using requestionAnimationFrame.

That loop function looks like this:

function loop() { 
    window.requestAnimationFrame(loop);
    drawArea.clearRect(0,0,w,h);

    for (let i = 0; i < particles.length; i++){
        particles[i].update();
        particles[i].draw();
    }
}

The loop function clears the canvas area, updates each particle position, and draws it; the constant refreshing with requestAnimationFrame() creates the impression of animation.

Everything is started by calling the setup() function, after setting a few other constants and variables and initializing the resizeReset function:

const canvasBody = document.getElementById("canvas"),
drawArea = canvasBody.getContext("2d");
let delay = 200, tid;
resizeReset();
setup();

At this point, the animation will look like a series of dots moving around the canvas:

See the Pen Dynamic Point Animation with HTML5 Canvas by aleen42 (@aleen42) on CodePen.

To create the mesh, we must add a little more code.

Creating the Lines

To draw the lines, the loop() function is added to, becoming:

function loop() { 
    window.requestAnimationFrame(loop);
    drawArea.clearRect(0, 0, w, h);

    for (let i = 0; i < particles.length; i++){
        particles[i].update();
        particles[i].draw();
    }

    for (let i = 0; i < particles.length; i++){
        linkPoints(particles[i], particles);
    }
}

The linkPoints function is called for every particle. That function also uses a piece of code called checkDistance:

let checkDistance = function (x1, y1, x2, y2) { 
    return Math.sqrt(Math.pow(x2 - x1, 2) + Math.pow(y2 - y1, 2));
};

The checkDistance function determines the distance between each point; if that distance is less than linkDistance, the calculated opacity of the line will be greater than 0, and it will be drawn between the matching points.

Before we get there, the rgb color is broken into its components:

let rgb = opts.lineColor.match(/\d+/g);

The linkPoints function checks each point against the other particles (referred to as "hubs" in the context of the function) and draws the line at the determined level of opacity, using template literals:

let linkPoints = function (point1, hubs) { 
    for (let i = 0; i < hubs.length; i++) {
        let distance = checkDistance(point1.x, point1.y, hubs[i].x, hubs[i].y);
        let opacity = 1 - distance / opts.linkRadius;

        if (opacity > 0) { 
            drawArea.lineWidth = 0.5;
            drawArea.strokeStyle = `rgba(${rgb[0]}, ${rgb[1]}, ${rgb[2]}, ${opacity})`;
            drawArea.beginPath();
            drawArea.moveTo(point1.x, point1.y);
            drawArea.lineTo(hubs[i].x, hubs[i].y);
            drawArea.closePath();
            drawArea.stroke();
        }
    }
}

Conclusion

The result (using aspects of ES6) is very efficient, and I encourage you to experiment with the various options in the script.

Note that the animation can be brought to its knees by adding too many points and/or too great a link distance (which creates too many lines). It would also be nice to have the speed of the particles slow down as the viewport narrows: at small sizes, the particles appear to move faster in a more confined space.

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