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【原】Canvas画笔的基本使用

 流楚丶格念 2022-01-14

文章目录

Canvas画笔的基本使用

图形绘制

需要理解些概念：

  • 路径的概念

  • 路径的绘制

    • 描边 stroke()
    • 填充 fill()

  • 闭合路径

    • 手动闭合
    • 程序闭合 closePath()

  • 填充规则(非零环绕)
    在这里插入图片描述

  • 开启新的路径 beginPath()

设置样式

  • 画笔的状态
    • lineWidth 线宽，默认1px
    • lineCap 线末端类型：(butt默认)、round、square
    • lineJoin 相交线的拐点 miter(默认)、round、bevel
    • strokeStyle 线的颜色
    • fillStyle 填充颜色
    • setLineDash() 设置虚线
    • getLineDash() 获取虚线宽度集合
    • lineDashOffset 设置虚线偏移量（负值向右偏移）

画笔实例练习

渐变色绘制

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        canvas {
            border: 1px solid #ccc;
        }
    </style>
</head>
<body>
<canvas width="600" height="400"></canvas>
<script>
    var myCanvas = document.querySelector('canvas');
    var ctx = myCanvas.getContext('2d');

    /*线是由点构成的*/
    ctx.lineWidth = 30;
    for (var i = 0; i < 255; i++) {
        ctx.beginPath();
        ctx.moveTo(100+i-1,100);
        ctx.lineTo(100+i,100);
        ctx.strokeStyle = 'rgb('+i+',0,0)';
        ctx.stroke();
    }

</script>
</body>
</html>

镂空的房子

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        canvas {
            border: 1px solid #ccc;
        }
    </style>
</head>
<body>
<canvas width="600" height="400"></canvas>
<script>
    var myCanvas = document.querySelector('canvas');
    var ctx = myCanvas.getContext('2d');

    /*1.绘制两个正方形 一大200一小100 套在一起*/
    ctx.moveTo(100,100);
    ctx.lineTo(300,100);
    ctx.lineTo(300,300);
    ctx.lineTo(100,300);
    ctx.closePath();

    ctx.moveTo(150,150);
    ctx.lineTo(150,250);
    ctx.lineTo(250,250);
    ctx.lineTo(250,150);
    ctx.closePath();

    /*2.去填充*/
    //ctx.stroke();
    ctx.fillStyle = 'red';
    ctx.fill();

    /*在填充的时候会遵循非零环绕规则*/
</script>
</body>
</html>

绘制坐标网格

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        canvas {
            border: 1px solid #ccc;
        }
    </style>
</head>
<body>
<canvas width="600" height="400"></canvas>
<script>
    var myCanvas = document.querySelector('canvas');
    var ctx = myCanvas.getContext('2d');

    /*1.绘制网格*/
    /*2.网格的大小*/
    var gridSize = 10;
    var canvasHeight = ctx.canvas.height;
    var canvasWidth = ctx.canvas.width;
    /*3.画多少条X轴方向的线 横线的条数  画布高度/小格大小  */

    var xLineTotal = Math.floor(canvasHeight / gridSize);
    for (var i = 0; i <= xLineTotal; i++) {
        ctx.beginPath();
        ctx.moveTo(0, i * gridSize - 0.5 );
        ctx.lineTo(canvasWidth, i * gridSize - 0.5);
        ctx.strokeStyle = '#eee';
        ctx.stroke();
    }
    /*4.画多少条Y轴方向的线*/
    var yLineTotal = Math.floor(canvasWidth / gridSize);
    for (var i = 0; i <= yLineTotal; i++) {
        ctx.beginPath();
        ctx.moveTo(i*gridSize - 0.5 ,0);
        ctx.lineTo(i*gridSize - 0.5 ,canvasHeight);
        ctx.strokeStyle = '#eee';
        ctx.stroke();
    }
</script>
</body>
</html>

绘制坐标系

在这里插入图片描述

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        canvas {
            border: 1px solid #ccc;
        }
    </style>
</head>
<body>
<canvas width="600" height="400"></canvas>
<script>
    var myCanvas = document.querySelector('canvas');
    var ctx = myCanvas.getContext('2d');

    /*1.绘制坐标系*/
    /*2.确定原点*/
    /*3.确定距离画布旁边的距离*/
    /*4.确定坐标轴的长度*/
    /*5.确定箭头的大小  是个等腰三角形  10 */
    /*6.绘制箭头填充*/

    // 坐标轴与底部的间隔
    var space = 20;
    // 箭头大小
    var arrowSize = 10; 

    /*计算原点 x0 y0*/
    var canvasWidth = ctx.canvas.width;
    var canvasHeight = ctx.canvas.height;
    var x0 = space;
    var y0 = canvasHeight - space;

    /*绘制x轴*/
    ctx.beginPath();
    ctx.moveTo(x0, y0);
    ctx.lineTo(canvasWidth - space, y0);
    /*箭头*/
    ctx.lineTo(canvasWidth - space - arrowSize, y0 + arrowSize / 2);
    ctx.lineTo(canvasWidth - space - arrowSize, y0 - arrowSize / 2);
    ctx.lineTo(canvasWidth - space, y0);
    ctx.fill();
    ctx.stroke();

    /*绘制y轴*/
    ctx.beginPath();
    ctx.moveTo(x0, y0);
    ctx.lineTo(space, space);
    /*箭头*/
    ctx.lineTo(space + arrowSize / 2, space + arrowSize);
    ctx.lineTo(space - arrowSize / 2, space + arrowSize);
    ctx.lineTo(space, space);
    ctx.fill();
    ctx.stroke();


</script>
</body>
</html>

绘制坐标点

在这里插入图片描述

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        canvas {
            border: 1px solid #ccc;
        }
    </style>
</head>
<body>
<canvas width="600" height="400"></canvas>
<script>
    var myCanvas = document.querySelector('canvas');
    var ctx = myCanvas.getContext('2d');

    /*1.绘制点*/
    /*2.点的尺寸*/
    /*3.以坐标中心绘制点*/

    /*点坐标*/
    var coordinate = {
        x:100,
        y:100
    }
    /*点尺寸*/
    var dottedSize = 10;

    ctx.moveTo(coordinate.x - dottedSize / 2,coordinate.y - dottedSize / 2);
    ctx.lineTo(coordinate.x + dottedSize / 2,coordinate.y - dottedSize / 2);
    ctx.lineTo(coordinate.x + dottedSize / 2,coordinate.y + dottedSize / 2);
    ctx.lineTo(coordinate.x - dottedSize / 2,coordinate.y + dottedSize / 2);
    ctx.closePath();
    ctx.fill();



</script>
</body>
</html>

绘制折线图

在这里插入图片描述

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>折线图</title>
    <style>
        canvas {
            border: 1px solid #ccc;
        }
    </style>
</head>
<body>
<canvas width="600" height="400"></canvas>
<script>
    /*1.构造函数*/
    var LineChart = function (ctx) {
        /*获取绘图工具*/
        this.ctx = ctx || document.querySelector('canvas').getContext('2d');
        /*画布的大小*/
        this.canvasWidth = this.ctx.canvas.width;
        this.canvasHeight = this.ctx.canvas.height;
        /*网格的大小*/
        this.gridSize = 10;
        /*坐标系的间距*/
        this.space = 20;
        /*坐标原点*/
        this.x0 = this.space;
        this.y0 = this.canvasHeight - this.space;
        /*箭头的大小*/
        this.arrowSize = 10;
        /*绘制点*/
        this.dottedSize = 6;
        /*点的坐标 和数据有关系  数据可视化*/
    }
    /*2.行为方法*/
    LineChart.prototype.init = function (data) {
        this.drawGrid();
        this.drawAxis();
        this.drawDotted(data);
    };
    /*绘制网格*/
    LineChart.prototype.drawGrid = function () {
        /*x方向的线*/
        var xLineTotal = Math.floor(this.canvasHeight / this.gridSize);
        this.ctx.strokeStyle = '#eee';
        for (var i = 0; i <= xLineTotal; i++) {
            this.ctx.beginPath();
            this.ctx.moveTo(0, i * this.gridSize - 0.5);
            this.ctx.lineTo(this.canvasWidth, i * this.gridSize - 0.5);
            this.ctx.stroke();
        }
        /*y方向的线*/
        var yLineTotal = Math.floor(this.canvasWidth / this.gridSize);
        for (var i = 0; i <= yLineTotal; i++) {
            this.ctx.beginPath();
            this.ctx.moveTo(i * this.gridSize - 0.5, 0);
            this.ctx.lineTo(i * this.gridSize - 0.5, this.canvasHeight);
            this.ctx.stroke();
        }
    };
    /*绘制坐标系*/
    LineChart.prototype.drawAxis = function () {
        /*X轴*/
        this.ctx.beginPath();
        this.ctx.strokeStyle = '#000';
        this.ctx.moveTo(this.x0, this.y0);
        this.ctx.lineTo(this.canvasWidth - this.space, this.y0);
        this.ctx.lineTo(this.canvasWidth - this.space - this.arrowSize, this.y0 + this.arrowSize / 2);
        this.ctx.lineTo(this.canvasWidth - this.space - this.arrowSize, this.y0 - this.arrowSize / 2);
        this.ctx.lineTo(this.canvasWidth - this.space, this.y0);
        this.ctx.stroke();
        this.ctx.fill();
        /*Y轴*/
        this.ctx.beginPath();
        this.ctx.strokeStyle = '#000';
        this.ctx.moveTo(this.x0, this.y0);
        this.ctx.lineTo(this.space, this.space);
        this.ctx.lineTo(this.space + this.arrowSize / 2, this.space + this.arrowSize);
        this.ctx.lineTo(this.space - this.arrowSize / 2, this.space + this.arrowSize);
        this.ctx.lineTo(this.space, this.space);
        this.ctx.stroke();
        this.ctx.fill();
    };
    /*绘制所有点*/
    LineChart.prototype.drawDotted = function (data) {
        /*1.数据的坐标 需要转换 canvas坐标*/
        /*2.再进行点的绘制*/
        /*3.把线连起来*/
        var that = this;
        /*记录当前坐标*/
        var prevCanvasX = 0;
        var prevCanvasY = 0;
        data.forEach(function (item, i) {
            /* x = 原点的坐标 + 数据的坐标 */
            /* y = 原点的坐标 - 数据的坐标 */
            console.log("item =");
            console.log(item);
            console.log( "i="+i);
            var canvasX = that.x0 + item.x;
            var canvasY = that.y0 - item.y;
            /*绘制点*/
            that.ctx.beginPath();
            that.ctx.moveTo(canvasX - that.dottedSize / 2, canvasY - that.dottedSize / 2);
            that.ctx.lineTo(canvasX + that.dottedSize / 2, canvasY - that.dottedSize / 2);
            that.ctx.lineTo(canvasX + that.dottedSize / 2, canvasY + that.dottedSize / 2);
            that.ctx.lineTo(canvasX - that.dottedSize / 2, canvasY + that.dottedSize / 2);
            that.ctx.closePath();
            that.ctx.fill();
            /*点的连线*/
            /*当时第一个点的时候 起点是 x0 y0*/
            /*当时不是第一个点的时候 起点是 上一个点*/
            if(i == 0){
                that.ctx.beginPath();
                that.ctx.moveTo(that.x0,that.y0);
                that.ctx.lineTo(canvasX,canvasY);
                that.ctx.stroke();
            }else{
                /*上一个点*/
                that.ctx.beginPath();
                that.ctx.moveTo(prevCanvasX,prevCanvasY);
                that.ctx.lineTo(canvasX,canvasY);
                that.ctx.stroke();
            }
            /*记录当前的坐标，下一次要用*/
            prevCanvasX = canvasX;
            prevCanvasY = canvasY;
        });
    };
    /*3.初始化*/
    var data = [
        {
            x: 100,
            y: 300
        },
        {
            x: 200,
            y: 160
        },
        {
            x: 300,
            y: 240
        },
        {
            x: 400,
            y: 120
        },
        {
            x: 500,
            y: 80
        }
    ];
    var lineChart = new LineChart();
    lineChart.init(data);
</script>
</body>
</html>

参考文档

  • w3school
  • Canvas_API

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