JS+Canvas achieves rain and snow effects-JS Tutorial-php.cn

I recently worked on a project, in which there was a need to realize the animation effects of rain and light snow, so I made a drop component here to show the common falling object effect of this canvas. Before I introduce the main text to you, let me show you the renderings:

Display the renderings:

Raining and snowing

JS+Canvas 实现下雨下雪效果

It seems that the effect is good. Compared with using created dom elements to create multi-object positioning animations, using canvas will be easier and faster, and the performance will be better

Calling code

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
#canvas{
width:100%;
height: 100%;
}
</style>
</head>
<body>
<canvas id="canvas"></canvas>
<script src="canvasDrop.js"></script>
<script>
canvasDrop.init({
type: "rain", // drop类型，有rain or snow
speed : [0.4,2.5], //速度范围
size_range: [0.5,1.5],//大小半径范围
hasBounce: true, //是否有反弹效果or false,
wind_direction: -105 //角度
hasGravity: true //是否有重力考虑
});
</script>
</body>
</html>

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Okay , let’s explain the simple implementation principle first. First, define some global variables we will use, such as wind direction angle, probability, object data, etc.

Define global variables

//定义两个对象数据
//分别是drops下落物体对象
//和反弹物体bounces对象
var drops = [], bounces = [];
//这里设定重力加速度为0.2/一帧
var gravity = 0.2;
var speed_x_x, //横向加速度
speed_x_y, //纵向加速度
wind_anger; //风向
//画布的像素宽高
var canvasWidth,
canvasHeight;
//创建drop的几率
var drop_chance;
//配置对象
var OPTS;
//判断是否有requestAnimationFrame方法，如果有则使用，没有则大约一秒30帧
window.requestAnimFrame =
window.requestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.oRequestAnimationFrame ||
window.msRequestAnimationFrame ||
function(callback) {
window.setTimeout(callback, 1000 / 30);
};

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Define core objects

Next we need to define several important objects. The organization needs to define relatively few objects. There are only three in total. Three core objects are defined in the entire drop component, which are as follows:

Vector speed object, with horizontal x, and vertical y speed size unit is: V = displacement pixel/frame

The understanding of Vector object is also very simple and crude, it is to record the falling object drop Speed/V

var Vector = function(x, y) {
//私有属性 横向速度x ,纵向速度y
this.x = x || 0;
this.y = y || 0;
};
//公有方法- add : 速度改变函数,根据参数对速度进行增加
//由于业务需求，考虑的都是下落加速的情况，故没有减速的，后期可拓展
/*
* @param v object || string 
*/
Vector.prototype.add = function(v) {
if (v.x != null && v.y != null) {
this.x += v.x;
this.y += v.y;
} else {
this.x += v;
this.y += v;
}
return this;
};
//公有方法- copy : 复制一个vector，来用作保存之前速度节点的记录
Vector.prototype.copy = function() {
//返回一个同等速度属性的Vector实例
return new Vector(this.x, this.y);
};
Drop 下落物体对象， 即上面效果中的雨滴和雪， 在后面你也可自己拓展为陨石或者炮弹
对于Drop对象其基本定义如下
//构造函数
var Drop = function() {
/* .... */
};
//公有方法-update 
Drop.prototype.update = function() {
/* .... */
};
//公有方法-draw
Drop.prototype.draw = function() {
/* .... */
};

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After reading the above three methods, have you guessed their functions? Next, let us understand what these three methods do

Constructor

The constructor is mainly responsible for defining the initial information of the drop object, such as speed, initial coordinates, size, acceleration, etc.

//构造函数 Drop
var Drop = function() {
//随机设置drop的初始坐标 
//首先随机选择下落对象是从从哪一边
var randomEdge = Math.random()*2;
if(randomEdge > 1){
this.pos = new Vector(50 + Math.random() * canvas.width, -80);
}else{
this.pos = new Vector(canvas.width, Math.random() * canvas.height);
}
//设置下落元素的大小
//通过调用的OPTS函数的半径范围进行随机取值
this.radius = (OPTS.size_range[0] + Math.random() * OPTS.size_range[1]) *DPR;
//获得drop初始速度
//通过调用的OPTS函数的速度范围进行随机取值
this.speed = (OPTS.speed[0] + Math.random() * OPTS.speed[1]) *DPR;
this.prev = this.pos;
//将角度乘以 0.017453293 （2PI/360）即可转换为弧度。
var eachAnger = 0.017453293; 
//获得风向的角度
wind_anger = OPTS.wind_direction * eachAnger;
//获得横向加速度 
speed_x = this.speed * Math.cos(wind_anger);
//获得纵向加速度
speed_y = - this.speed * Math.sin(wind_anger);
//绑定一个速度实例
this.vel = new Vector(wind_x, wind_y);
};

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The update method of the Drop object

The update method is responsible for each frame Changes in attributes of the drop instance such as changes in displacement

Drop.prototype.update = function() {
this.prev = this.pos.copy();
//如果是有重力的情况，则纵向速度进行增加
if (OPTS.hasGravity) {
this.vel.y += gravity;
}
//
this.pos.add(this.vel);
};

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The draw method of the Drop object

The draw method is responsible for the painting of the drop instance in each frame

Drop.prototype.draw = function() {
ctx.beginPath();
ctx.moveTo(this.pos.x, this.pos.y);
//目前只分为两种情况，一种是rain 即贝塞尔曲线
if(OPTS.type =="rain"){
ctx.moveTo(this.prev.x, this.prev.y);
var ax = Math.abs(this.radius * Math.cos(wind_anger));
var ay = Math.abs(this.radius * Math.sin(wind_anger));
ctx.bezierCurveTo(this.pos.x + ax, this.pos.y + ay, this.prev.x + ax , this.prev.y + ay, this.pos.x, this.pos.y);
ctx.stroke();
//另一种是snow--即圆形
}else{
ctx.moveTo(this.pos.x, this.pos.y);
ctx.arc(this.pos.x, this.pos.y, this.radius, 0, Math.PI*2);
ctx.fill();
}
};

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bounce The falling bounce object is the water droplet bounced by the rain above. You can also later expand it to rebound gravel or smoke

The definition is very simple , I will not give a detailed explanation here

var Bounce = function(x, y) {
var dist = Math.random() * 7;
var angle = Math.PI + Math.random() * Math.PI;
this.pos = new Vector(x, y);
this.radius = 0.2+ Math.random()*0.8;
this.vel = new Vector(
Math.cos(angle) * dist,
Math.sin(angle) * dist
);
};
Bounce.prototype.update = function() {
this.vel.y += gravity;
this.vel.x *= 0.95;
this.vel.y *= 0.95;
this.pos.add(this.vel);
};
Bounce.prototype.draw = function() {
ctx.beginPath();
ctx.arc(this.pos.x, this.pos.y, this.radius*DPR, 0, Math.PI * 2);
ctx.fill();
};

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External interface

update

is equivalent to the start function of the entire canvas animation

function update() {
var d = new Date;
//清理画图
ctx.clearRect(0, 0, canvas.width, canvas.height);
var i = drops.length;
while (i--) {
var drop = drops[i];
drop.update();
//如果drop实例下降到底部，则需要在drops数组中清楚该实例对象
if (drop.pos.y >= canvas.height) {
//如果需要回弹，则在bouncess数组中加入bounce实例
if(OPTS.hasBounce){
var n = Math.round(4 + Math.random() * 4);
while (n--)
bounces.push(new Bounce(drop.pos.x, canvas.height));
}
//如果drop实例下降到底部，则需要在drops数组中清楚该实例对象
drops.splice(i, 1);
}
drop.draw();
}
//如果需要回弹
if(OPTS.hasBounce){
var i = bounces.length;
while (i--) {
var bounce = bounces[i];
bounce.update();
bounce.draw();
if (bounce.pos.y > canvas.height) bounces.splice(i, 1);
}
}
//每次产生的数量
if(drops.length < OPTS.maxNum){
if (Math.random() < drop_chance) {
var i = 0,
len = OPTS.numLevel;
for(; i<len; i++){
drops.push(new Drop());
}
}
}
//不断循环update
requestAnimFrame(update);
}

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init

The init interface initializes all basic properties of the entire canvas, such as obtaining the pixel ratio of the screen and setting the pixel size of the canvas. , and style settings

function init(opts) {
OPTS = opts;
canvas = document.getElementById(opts.id);
ctx = canvas.getContext("2d");
////兼容高清屏幕，canvas画布像素也要相应改变
DPR = window.devicePixelRatio;
//canvas画板像素大小， 需兼容高清屏幕，故画板canvas长宽应该乘于DPR
canvasWidth = canvas.clientWidth * DPR;
canvasHeight =canvas.clientHeight * DPR;
//设置画板宽高
canvas.width = canvasWidth;
canvas.height = canvasHeight;
drop_chance = 0.4;
//设置样式
setStyle();
}
function setStyle(){
if(OPTS.type =="rain"){
ctx.lineWidth = 1 * DPR;
ctx.strokeStyle = &#39;rgba(223,223,223,0.6)&#39;;
ctx.fillStyle = &#39;rgba(223,223,223,0.6)&#39;;
}else{
ctx.lineWidth = 2 * DPR;
ctx.strokeStyle = &#39;rgba(254,254,254,0.8)&#39;;
ctx.fillStyle = &#39;rgba(254,254,254,0.8)&#39;;
}
}

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Conclusion

Okay, a simple drop component has been completed. Of course, there are many shortcomings in it. Perfect, after writing this drop component, I believe that there are many places to explore in the H5 scene for the animation implementation of canvas.

Finally, let’s talk about the shortcomings and later work:

0. This component currently does not have enough external interfaces, the adjustable range is not very large, and the abstraction is not very thorough

1. setStyle sets the basic style

2. Customization of the update and draw methods of Drop and Bounce objects, allowing users to set more falling speed and size changes The form and style effect

3. Interfaces for animation pause, acceleration and deceleration operations should be added

The above is the JS and Canvas implementation introduced by the editor I hope this knowledge about the effect of rain and snow will be helpful to you. If you have any questions, please leave me a message and the editor will reply to you in time. I would also like to thank you all for your support of the PHP Chinese website!

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