cancas html5

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实现原理

1. canvas里面实现描边文字

2. 利用getImageData获得描边文字的像素矩阵

3. 将粒子效果绑定在描边文字上

整个效果如下。

html文件非常简单。

[html] view plaincopy

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

css文件如下。

[css] view plaincopy

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。

[javascript] view plaincopy

BLUR = false;
PULSATION = true;
PULSATION_PERIOD = 1000;
PARTICLE_RADIUS = 6;
/* 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 = ["海庆", "深爱", "春玲", "直到","永远"];
QUALITY_TO_FONT_SIZE = [10, 12, 40, 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,20, 60);
//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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