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Home > Web Front-end > H5 Tutorial > Canvas realizes the drawing of rotating windmill

Canvas realizes the drawing of rotating windmill

php中世界最好的语言
Release： 2018-03-27 09:23:44
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This time I will bring you the drawing of rotating windmills with Canvas. What are the precautions for drawing rotating windmills with Canvas? Here are the actual cases, let’s take a look.

Before teaching, I think if you are smart, you have mastered the basic basic operation methods of Canvas. If you don’t know much about Canvas, then I suggest you go to http://www.w3school.com.cn /tags/html_ref_canvas.asp Get familiar with it first;

okey! The picture below is the simple effect after we complete it. Action is not as good as action, so let’s do a simple drawing!

1. Define the canvas

First of all, we insert the tag into the html file to define the size of the canvas. The size of the canvas defined here is 800*600 pixels. At the same time, set the background color of the canvas in the internal style sheet (convenient for viewing when drawing); 

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style type="text/css">
        body{
            padding: 0;
            margin: 0;
        }
        #canvas {
            background:#5151a2;
        }
    </style>
</head>
<body>
    <canvas id="canvas" width="800" height="600"></canvas>
</body>
</html>　
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The next core is to draw the windmill in the native JS environment; through JS

DOM operation method Obtain the canvas element object and obtain the 2D drawing context through getContex("2d"). This method is like telling the browser "We want to draw 2D graphics on this canvas"; 

<script type="text/javascript">
    //获取画布的2d上下文
    var ctx = document.getElementById("canvas").getContext("2d");
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2. Draw the base of the windmill

The geometric figure of the base of the windmill looks like a long and slender trapezoid. We can draw a trapezoid and then fill it with color. Here, in order to achieve a relatively small Good effect, using the color gradient filling method; okey! Just look at the code~~! 

    //定义一个函数 ，封装风车的底部基座
    function buttom(){
        ctx.beginPath();                                        //开始一条新的绘制路径
        var liner = ctx.createLinearGradient(390,600,410,600);    //设置变量（颜色渐变的方向-起点-终点）
        liner.addColorStop(0,"#ccc");                            //设置起点颜色
        liner.addColorStop(0.5,"#fff");                            //设置中点颜色
        liner.addColorStop(1,"#ccc");                            //设置终点颜色
        ctx.fillStyle = liner;                                    //梯形的填充方式设置为 变量（渐变颜色）    
        ctx.moveTo(395,300);                                    //提起我们的画笔，起点设置为（395,300）
        ctx.lineTo(405,300);                                    //连接起点画线
        ctx.lineTo(410,600);
        ctx.lineTo(390,600);                                    
        ctx.closePath();                                        //闭合路径
        ctx.fill();                                                //填充梯形
        
    }
　　buttom();　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　//要调用函数，才能在浏览器显示
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Let’s take a look at the effect on the page. Is it very simple?

(I feel like I talk a bit too much~!~!)

3. Draw leaves

The next part will be the most critical part of this animation. First, let’s analyze the structure of the leaves. The angle between the three leaves is 120°, and the shape of each leaf is the same; they have a center, and you may also have one in your mind. I have a question, should I draw the center of the circle first or the leaves first? How should I draw the shape of the leaves? Can the leaves be copied and pasted? The answer is of course yes, Let's do it!

Idea analysis:

1). Since the shapes of the three leaves are exactly the same, we only need to draw one leaf, and just copy the second and third leaves directly. We are smart Shouldn't we encapsulate a function for this leaf drawing method? Just call it the bind( ) function! ! Just call it every time! Why! You guys are so smart

2). The three leaves have a center of a circle. In order to facilitate the coordinate values ​​when drawing the leaves, we move the center of the circle from the upper left corner of the drawing to the top of the trapezoid, so that it will be much more convenient for us to draw the leaves. ! The translate() method is used here to move the coordinate system!

3) The most difficult point is to understand how the animation is implemented here, because the animation principle will affect the document structure of our leaf drawing:

First we create a new drawing environment, we Call it environment 1. We draw the first leaf on environment 1; then rotate 120° to create the first drawing environment 2 under the premise of the first drawing environment, and then call the function bind( ) for drawing leaves. , draw two leaves; the third leaf is drawn in the same way, rotate 120° on the basis of environment 2, create a new environment 3, and call the leaf drawing function bind( ) to draw the third leaf;

If you want To implement animation, we only need to rotate the drawing environment 1 of the first leaf. The second leaf and the third leaf are drawn with reference to environment 1. Do they also move? ? Barrage: 666666

4), and finally some basic appearance style debugging! For example, color gradient, transparency, etc.!

Drawing leaves

When I drew this leaf shape, I adjusted it slowly. My aesthetics are quite low, forgive me. I can only draw such leaves. Of course, students with rich imagination can draw them according to their own preferences, but the general idea is the same;

Here I declare a variable var num = 0;, as the environment 1 rotation A parameter of degree change: Then let’s look at the code directly! ! ! 

var num =0;
function yezi(){
        ctx.save();  //保存默认情况下的canvas变换状态
        ctx.beginPath();
        ctx.translate(400,300);
        // ctx.globalAlpha = 0.9;
        // 设置第一次状态下 坐标系旋转度数
        ctx.rotate((Math.PI/180)*num);
        var liner1 = ctx.createLinearGradient(30,-12,30,12);      //这里设置颜色渐变填充的样式
            liner1.addColorStop(0,"#ccc");
            liner1.addColorStop(0.5,"#fff");
            liner1.addColorStop(1,"#ccc");
            ctx.fillStyle = liner1;
        ctx.save();                 //保存第一次状态  平移坐标系变换
            ctx.beginPath();
            bind();                //调用函数
            //绘制第二片叶子
            ctx.beginPath();
            ctx.rotate((Math.PI/180)*120);   //坐标系旋转120°
            ctx.save();                        //保存旋转坐标系状态，为第三片叶子做铺垫
                bind();            //调用函数
                //绘制第三片叶子
                ctx.beginPath();
                ctx.rotate((Math.PI/180)*120);   //坐标系旋转120°
                ctx.save();    
                    bind();     //调用函数
                ctx.restore();    //回复第3次状态前（旋转坐标系）
            ctx.restore();        //回复第2次状态前（旋转坐标系）
            //绘制叶子中心圆圈
            ctx.beginPath();
            var arcgradient = ctx.createRadialGradient(0,0,0,0,0,16);
            arcgradient.addColorStop(0,"#ccc");
            arcgradient.addColorStop(0.1,"#fff");
            arcgradient.addColorStop(1,"#ccc");
            ctx.arc(0,0,10,0,Math.PI*2);
            ctx.fillStyle  = arcgradient;
            ctx.fill();
        ctx.restore();             //回复第1次状态前（平移坐标系）
        num+=5;   //第一状下  环境1   态坐标系旋转度数增加********************************这个num使得环境1的旋转角度在不停的变化，**********************************************
        ctx.restore();
    }
    //绘制每片叶子都重复的代码，这里做一个函数包装
    function bind(){
        ctx.moveTo(0,0);                    
        ctx.quadraticCurveTo(10,-12,30,-12);　　　　//比赛尔曲线
        ctx.lineTo(190,-3);
        ctx.quadraticCurveTo(200,0,190,3);　　　　
        ctx.lineTo(30,12);
        ctx.moveTo(0,0);
        ctx.quadraticCurveTo(10,12,30,12);
        ctx.fill();
    }
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4、设置动画

动画这部分就比较简单了，设置定时器，清除画布，调用函数；大功告成，打完收工！！！

setInterval(function(){
        ctx.clearRect(0,0,800,600);　　　　//每次执行代码前，都要将画布清空，不然画出的图形会滞留在画布上；
        buttom();　　　　　　　　　　　　　　　//调用函数　
        yezi();
    },50);
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相信看了本文案例你已经掌握了方法，更多精彩请关注php中文网其它相关文章！

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