70 lines
1.9 KiB
JavaScript
70 lines
1.9 KiB
JavaScript
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/**
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* Created by troyxu on 16/12/6.
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*/
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var Dots = function () {
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// 画布相关
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this.canvas;
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this.ctx;
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// 绘制点相关
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this.x;
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this.y;
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this.r;
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// 移动相关
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this.sx;
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this.sy;
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};
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Dots.prototype = {
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// 初始化点的方法 x/y为可选参数 为生成点的位置 不传则随机生成
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init: function (canvas, x, y) {
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this.canvas = canvas;
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this.ctx = this.canvas.getContext('2d');
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this.x = x*2 || Math.random() * this.canvas.width;
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this.y = y*2 || Math.random() * this.canvas.height;
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this.r = Math.random() * 4; // 随机生成 <4 的半径值
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// 随机确定点的移动速度与方向 速度值在 [-2, 2) 之间 提高数值可加快速度
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this.sx = Math.random() * 4 - 2;
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this.sy = Math.random() * 4 - 2;
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this.ctx.beginPath();
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this.ctx.arc(this.x, this.y, this.r, 0, 2*Math.PI);
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this.ctx.fillStyle = "rgba(255,255,255,.8)";
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this.ctx.fill();
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this.ctx.closePath();
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},
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// 更新点位置
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update: function () {
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this.x = this.x + this.sx;
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this.y = this.y + this.sy;
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// 点超出canvas范围时另其"重生"
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if (this.x < 0 || this.x > this.canvas.width) {
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this.init(this.canvas);
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}
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if (this.y < 0 || this.y > this.canvas.height) {
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this.init(this.canvas);
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}
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this.ctx.beginPath();
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this.ctx.arc(this.x, this.y, this.r + 0.5, 0, 2*Math.PI);
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this.ctx.fillStyle = "rgba(255,255,255,.8)";
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this.ctx.fill();
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this.ctx.closePath();
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},
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// 跟踪鼠标的点的位置更新 x/y为鼠标位置
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mouseDot: function (x, y) {
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this.x = x*2;
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this.y = y*2;
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this.ctx.beginPath();
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this.ctx.arc(this.x, this.y, this.r + 0.5, 0, 2*Math.PI);
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this.ctx.fillStyle = "rgba(255,0,0,.8)";
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this.ctx.fill();
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this.ctx.closePath();
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}
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};
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