キャンバスに黒い背景で赤い花火を作る方法

今回はキャンバスを使って黒背景の赤い花火を作る方法を紹介します。 キャンバスを使って黒背景の赤い花火を作るときの注意点は何ですか。実際の事例を見てみましょう。

html

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

css

body {    background: #000;    margin: 0;
}canvas {    cursor: crosshair;    display: block;}

js

// when animating on canvas, it is best to use requestAnimationFrame instead of setTimeout or setInterval// not supported in all browsers though and sometimes needs a prefix, so we need a shimwindow.requestAnimFrame = (function () {    return window.requestAnimationFrame ||        window.webkitRequestAnimationFrame ||        window.mozRequestAnimationFrame ||        function (callback) {            window.setTimeout(callback, 1000 / 60);
        };
})();// now we will setup our basic variables for the demovar canvas = document.getElementById('canvas'),
    ctx = canvas.getContext('2d'),    // full screen dimensions
    cw = window.innerWidth,
    ch = window.innerHeight,    // firework collection
    fireworks = [],    // particle collection
    particles = [],    // starting hue
    hue = 120,    // when launching fireworks with a click, too many get launched at once without a limiter, one launch per 5 loop ticks
    limiterTotal = 5,
    limiterTick = 0,    // this will time the auto launches of fireworks, one launch per 80 loop ticks
    timerTotal = 80,
    timerTick = 0,
    mousedown = false,    // mouse x coordinate,
    mx,    // mouse y coordinate
    my;// set canvas dimensionscanvas.width = cw;
canvas.height = ch;// now we are going to setup our function placeholders for the entire demo// get a random number within a rangefunction random(min, max) {    return Math.random() * (max - min) + min;
}// calculate the distance between two pointsfunction calculateDistance(p1x, p1y, p2x, p2y) {    var xDistance = p1x - p2x,
        yDistance = p1y - p2y;    return Math.sqrt(Math.pow(xDistance, 2) + Math.pow(yDistance, 2));
}// create fireworkfunction Firework(sx, sy, tx, ty) {    // actual coordinates
    this.x = sx;    this.y = sy;    // starting coordinates
    this.sx = sx;    this.sy = sy;    // target coordinates
    this.tx = tx;    this.ty = ty;    // distance from starting point to target
    this.distanceToTarget = calculateDistance(sx, sy, tx, ty);    this.distanceTraveled = 0;    // track the past coordinates of each firework to create a trail effect, increase the coordinate count to create more prominent trails
    this.coordinates = [];    this.coordinateCount = 3;    // populate initial coordinate collection with the current coordinates
    while (this.coordinateCount--) {        this.coordinates.push([this.x, this.y]);
    }    this.angle = Math.atan2(ty - sy, tx - sx);    this.speed = 2;    this.acceleration = 1.05;    this.brightness = random(50, 70);    // circle target indicator radius
    this.targetRadius = 1;
}// update fireworkFirework.prototype.update = function (index) {    // remove last item in coordinates array
    this.coordinates.pop();    // add current coordinates to the start of the array
    this.coordinates.unshift([this.x, this.y]);    // cycle the circle target indicator radius
    if (this.targetRadius < 8) {        this.targetRadius += 0.3;
    } else {        this.targetRadius = 1;
    }    // speed up the firework
    this.speed *= this.acceleration;    // get the current velocities based on angle and speed
    var vx = Math.cos(this.angle) * this.speed,
        vy = Math.sin(this.angle) * this.speed;    // how far will the firework have traveled with velocities applied?
    this.distanceTraveled = calculateDistance(this.sx, this.sy, this.x + vx, this.y + vy);    // if the distance traveled, including velocities, is greater than the initial distance to the target, then the target has been reached
    if (this.distanceTraveled >= this.distanceToTarget) {
        createParticles(this.tx, this.ty);        // remove the firework, use the index passed into the update function to determine which to remove
        fireworks.splice(index, 1);
    } else {        // target not reached, keep traveling
        this.x += vx;        this.y += vy;
    }
}// draw fireworkFirework.prototype.draw = function () {
    ctx.beginPath();    // move to the last tracked coordinate in the set, then draw a line to the current x and y
    ctx.moveTo(this.coordinates[this.coordinates.length - 1][0], this.coordinates[this.coordinates.length - 1][        1
    ]);
    ctx.lineTo(this.x, this.y);
    ctx.strokeStyle = &#39;hsl(&#39; + hue + &#39;, 100%, &#39; + this.brightness + &#39;%)&#39;;
    ctx.stroke();
    ctx.beginPath();    // draw the target for this firework with a pulsing circle
    ctx.arc(this.tx, this.ty, this.targetRadius, 0, Math.PI * 2);
    ctx.stroke();
}// create particlefunction Particle(x, y) {    this.x = x;    this.y = y;    // track the past coordinates of each particle to create a trail effect, increase the coordinate count to create more prominent trails
    this.coordinates = [];    this.coordinateCount = 5;    while (this.coordinateCount--) {        this.coordinates.push([this.x, this.y]);
    }    // set a random angle in all possible directions, in radians
    this.angle = random(0, Math.PI * 2);    this.speed = random(1, 10);    // friction will slow the particle down
    this.friction = 0.95;    // gravity will be applied and pull the particle down
    this.gravity = 1;    // set the hue to a random number +-20 of the overall hue variable
    this.hue = random(hue - 20, hue + 20);    this.brightness = random(50, 80);    this.alpha = 1;    // set how fast the particle fades out
    this.decay = random(0.015, 0.03);
}// update particleParticle.prototype.update = function (index) {    // remove last item in coordinates array
    this.coordinates.pop();    // add current coordinates to the start of the array
    this.coordinates.unshift([this.x, this.y]);    // slow down the particle
    this.speed *= this.friction;    // apply velocity
    this.x += Math.cos(this.angle) * this.speed;    this.y += Math.sin(this.angle) * this.speed + this.gravity;    // fade out the particle
    this.alpha -= this.decay;    // remove the particle once the alpha is low enough, based on the passed in index
    if (this.alpha <= this.decay) {
        particles.splice(index, 1);
    }
}// draw particleParticle.prototype.draw = function () {
    ctx.beginPath();    // move to the last tracked coordinates in the set, then draw a line to the current x and y
    ctx.moveTo(this.coordinates[this.coordinates.length - 1][0], this.coordinates[this.coordinates.length - 1][        1
    ]);
    ctx.lineTo(this.x, this.y);
    ctx.strokeStyle = &#39;hsla(&#39; + this.hue + &#39;, 100%, &#39; + this.brightness + &#39;%, &#39; + this.alpha + &#39;)&#39;;
    ctx.stroke();
}// create particle group/explosionfunction createParticles(x, y) {    // increase the particle count for a bigger explosion, beware of the canvas performance hit with the increased particles though
    var particleCount = 30;    while (particleCount--) {
        particles.push(new Particle(x, y));
    }
}// main demo loopfunction loop() {    // this function will run endlessly with requestAnimationFrame
    requestAnimFrame(loop);    // increase the hue to get different colored fireworks over time
    hue += 0.5;    // normally, clearRect() would be used to clear the canvas
    // we want to create a trailing effect though
    // setting the composite operation to destination-out will allow us to clear the canvas at a specific opacity, rather than wiping it entirely
    ctx.globalCompositeOperation = &#39;destination-out&#39;;    // decrease the alpha property to create more prominent trails
    ctx.fillStyle = &#39;rgba(0, 0, 0, 0.5)&#39;;
    ctx.fillRect(0, 0, cw, ch);    // change the composite operation back to our main mode
    // lighter creates bright highlight points as the fireworks and particles overlap each other
    ctx.globalCompositeOperation = &#39;lighter&#39;;    var text = "HAPPY NEW YEAR !";
    ctx.font = "50px sans-serif";    var textData = ctx.measureText(text);
    ctx.fillStyle = "rgba(" + parseInt(random(0, 255)) + "," + parseInt(random(0, 255)) + "," + parseInt(random(0,        255)) + ",0.3)";
    ctx.fillText(text, cw / 2 - textData.width / 2, ch / 2);    // loop over each firework, draw it, update it
    var i = fireworks.length;    while (i--) {
        fireworks[i].draw();
        fireworks[i].update(i);
    }    // loop over each particle, draw it, update it
    var i = particles.length;    while (i--) {
        particles[i].draw();
        particles[i].update(i);
    }    // launch fireworks automatically to random coordinates, when the mouse isn&#39;t down
    if (timerTick >= timerTotal) {        if (!mousedown) {            // start the firework at the bottom middle of the screen, then set the random target coordinates, the random y coordinates will be set within the range of the top half of the screen
            for (var h = 0; h < 50; h++) {
                fireworks.push(new Firework(cw / 2, ch / 2, random(0, cw), random(0, ch)));
            }
            timerTick = 0;
        }
    } else {
        timerTick++;
    }    // limit the rate at which fireworks get launched when mouse is down
    if (limiterTick >= limiterTotal) {        if (mousedown) {            // start the firework at the bottom middle of the screen, then set the current mouse coordinates as the target
            fireworks.push(new Firework(cw / 2, ch / 2, mx, my));
            limiterTick = 0;
        }
    } else {
        limiterTick++;
    }
}// mouse event bindings// update the mouse coordinates on mousemovecanvas.addEventListener(&#39;mousemove&#39;, function (e) {
    mx = e.pageX - canvas.offsetLeft;
    my = e.pageY - canvas.offsetTop;
});// toggle mousedown state and prevent canvas from being selectedcanvas.addEventListener(&#39;mousedown&#39;, function (e) {
    e.preventDefault();
    mousedown = true;
});
canvas.addEventListener(&#39;mouseup&#39;, function (e) {
    e.preventDefault();
    mousedown = false;
});// once the window loads, we are ready for some fireworks!window.onload = loop;

この記事の事例を読んだ後は、この方法を習得したと思います。さらに興味深い内容については、PHP 中国語 Web サイトの他の関連記事に注目してください。

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JS の async/await

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以上がキャンバスに黒い背景で赤い花火を作る方法の詳細内容です。詳細については、PHP 中国語 Web サイトの他の関連記事を参照してください。