POJ2236 wireless network 【并查集水题】

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今天是个好日子，2014年5月20日，表白的最佳时机，虽说孩子已经四岁、结婚已经五年，但是也不可以偷懒，于是有了这个效果。

在线研究点这里，下载收藏点这里。程序猿and程序媛，大胆秀出你的爱吧。

利用html5 canvas实现动态的文字粒子效果，效果如下。

OK，简单看看原理，首先我们需要在canvas里面实现描边文字，然后利用getImageData获得描边文字的像素矩阵，将粒子效果绑定在描边文章上。

整个效果如下。

html文件非常简单。

<canvas id="canvas" width="1000" height="600"></canvas>

css文件如下。

body {
	background: #000;
	text-align: center;
	font-family: "simhei"
}
canvas {
	margin: auto;
	position: absolute;
	left: 0;
	right:0;
	top: 0;
	bottom: 0;
}

js文件至关重要了。

BLUR = false;

PULSATION = true;
PULSATION_PERIOD = 1000;
PARTICLE_RADIUS = 1;

/* disable blur before using blink */

BLINK = false;

GLOBAL_PULSATION = false;

QUALITY = 2; /* 0 - 5 */

/* set false if you prefer rectangles */
ARC = true;

/* trembling + blur = fun */
TREMBLING = 0; /* 0 - infinity */

FANCY_FONT = "Arial";

BACKGROUND = "#000";

BLENDING = true;

/* if empty the text will be a random number */
var TEXT;
num = 0;
TEXTArray = ["Whq", "Love", "Xcl", "Ever"];

QUALITY_TO_FONT_SIZE = [10, 12, 30, 50, 200, 350];
QUALITY_TO_SCALE = [20, 6, 4, 1, 0.9, 0.5];
QUALITY_TO_TEXT_POS = [10, 20, 40, 60, 170, 280];

window.onload = function () {
    document.body.style.backgroundColor = BACKGROUND;

    var canvas = document.getElementById("canvas");
    var ctx = canvas.getContext("2d");

    var W = canvas.width;
    var H = canvas.height;

    var tcanvas = document.createElement("canvas");
    var tctx = tcanvas.getContext("2d");
    tcanvas.width = W;
    tcanvas.height = H;

    total_area = W * H;
    total_particles = 1000;
    single_particle_area = total_area / total_particles;
    area_length = Math.sqrt(single_particle_area);

    var particles = [];
    for (var i = 1; i <= total_particles; i++) {
        particles.push(new particle(i));
    }

    function particle(i) {
        this.r = Math.round(Math.random() * 255 | 0);
        this.g = Math.round(Math.random() * 255 | 0);
        this.b = Math.round(Math.random() * 255 | 0);
        this.alpha = 1;

        this.x = (i * area_length) % W;
        this.y = (i * area_length) / W * area_length;

        /* randomize delta to make particles sparkling */
        this.deltaOffset = Math.random() * PULSATION_PERIOD | 0;

        this.radius = 0.1 + Math.random() * 2;
    }

 	var positions = [];

	function new_positions() {

        TEXT = TEXTArray[num];

        if (num < TEXTArray.length - 1) {
            num++;
        } else {
            num = 0;
        }
        //alert(TEXT);

        tctx.fillStyle = "white";
        tctx.fillRect(0, 0, W, H)
        tctx.fill();

        tctx.font = "bold " + QUALITY_TO_FONT_SIZE[QUALITY] + "px " + FANCY_FONT;

        tctx.strokeStyle = "black";
        tctx.fillStyle="#f00";
        tctx.strokeText(TEXT,30, 50);
        //tctx.fillText(TEXT,30, 50);

        image_data = tctx.getImageData(0, 0, W, H);
        pixels = image_data.data;
        positions = [];
        for (var i = 0; i < pixels.length; i = i + 2) {
            if (pixels[i] != 255) {
                position = {
                    x: (i / 2 % W | 0) * QUALITY_TO_SCALE[QUALITY] | 0,
                    y: (i / 2 / W | 0) * QUALITY_TO_SCALE[QUALITY] | 0
                }
                positions.push(position);
            }
        }

        get_destinations();
    }

    function draw() {

        var now = Date.now();

        ctx.globalCompositeOperation = "source-over";

        if (BLUR) ctx.globalAlpha = 0.1;
        else if (!BLUR && !BLINK) ctx.globalAlpha = 1.0;

        ctx.fillStyle = BACKGROUND;
        ctx.fillRect(0, 0, W, H)

        if (BLENDING) ctx.globalCompositeOperation = "lighter";

        for (var i = 0; i < particles.length; i++) {

            p = particles[i];

            if (isNaN(p.x)) continue

            ctx.beginPath();
            ctx.fillStyle = "rgb(" + p.r + ", " + p.g + ", " + p.b + ")";
            ctx.fillStyle = "rgba(" + p.r + ", " + p.g + ", " + p.b + ", " + p.alpha + ")";

            if (BLINK) ctx.globalAlpha = Math.sin(Math.PI * mod * 1.0);

            if (PULSATION) { /* this would be 0 -> 1 */
                var mod = ((GLOBAL_PULSATION ? 0 : p.deltaOffset) + now) % PULSATION_PERIOD / PULSATION_PERIOD;
                mod = Math.sin(mod * Math.PI);
            } else var mod = 1;

            var offset = TREMBLING ? TREMBLING * (-1 + Math.random() * 2) : 0;

            var radius = PARTICLE_RADIUS * p.radius;

            if (!ARC) {
                ctx.fillRect(offset + p.x - mod * radius / 2 | 0, offset + p.y - mod * radius / 2 | 0, radius * mod,
                    radius * mod);
            } else {
                ctx.arc(offset + p.x | 0, offset + p.y | 0, radius * mod, Math.PI * 2, false);
                ctx.fill();
            }

            p.x += (p.dx - p.x) / 10;
            p.y += (p.dy - p.y) / 10;
        }
    }

    function get_destinations() {
        for (var i = 0; i < particles.length; i++) {
            pa = particles[i];
            particles[i].alpha = 1;
            var distance = [];
            nearest_position = 0;
            if (positions.length) {
                for (var n = 0; n < positions.length; n++) {
                    po = positions[n];
                    distance[n] = Math.sqrt((pa.x - po.x) * (pa.x - po.x) + (pa.y - po.y) * (pa.y - po.y));
                    if (n > 0) {
                        if (distance[n] <= distance[nearest_position]) {
                            nearest_position = n;
                        }
                    }
                }
                particles[i].dx = positions[nearest_position].x;
                particles[i].dy = positions[nearest_position].y;
                particles[i].distance = distance[nearest_position];

                var po1 = positions[nearest_position];
                for (var n = 0; n < positions.length; n++) {
                    var po2 = positions[n];
                    distance = Math.sqrt((po1.x - po2.x) * (po1.x - po2.x) + (po1.y - po2.y) * (po1.y - po2.y));
                    if (distance <= 5) {
                        positions.splice(n, 1);
                    }
                }
            } else {
                //particles[i].alpha = 0;
            }
        }
    }

    function init() {
        new_positions();
        setInterval(draw, 30);
        setInterval(new_positions, 2000);
    }

    init();
};

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POJ2236 wireless network 【并查集水题】