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前端畫圖canvas基本操作

基礎程式碼

html5:

<canvas id="canvas"></canvas>

js程式碼：

var canvasHeight = 600var canvasWidht = 800var canvas = document.getElementById("canvas")var context = canvas.getContext("2d")canvas.width = canvasWidhtcanvas.height = canvasHeight
canvas元素預設寬高300*150canvas元素的大小與繪圖表面大小：canvas元素有兩套實際上的尺寸。一個是元素本身大小：可以透過width和height設定（使用這種方法可以設定canvas元素和繪圖表面大小）一個是元素繪圖表面的大小：可以使用css設定（不要使用這種方法，只使用css設定寬高，如果元素大小和表面大小不一致，瀏覽器會放縮後者）canvas.getContext("2d") 中2d需要小寫直線
context.save()context.moveTo(0, 0)context.lineTo(200, 100)context.stroke()context.restore()
save 和restore : 儲存和恢復當前canvas環境的所有屬性；例如：需要在背景中畫細不同的網格線，然後用粗線在網格上進行後續繪圖。這種情況下需要臨時性地修改lineWidth屬性。矩形 
context.save()context.beginPath()context.strokeStyle = "red"context.rect(250, 100, 100, 80)// context.fillRect(250, 100, 100, 80)context.stroke()//context.fill()context.closePath()context.restore()
context.rect(x,y,width,height);context.stroke() 繪製空心圖形，context.fill() 填充圖形圓形 
context.save()context.beginPath()context.strokeStyle = "red"context.fillStyle = "red"context.arc(200, 100, 50, 0, Math.PI * 2)context.stroke()//context.fill()context.closePath()context.restore()
arc(x,y,r,start,stop) 繪製圓context.stroke() 空心圖形 ，context.fill()填充圖形三角形

等腰三角形

var height = 200 * Math.sin(Math.PI / 3); //計算等邊三角形的高context.moveTo(100, 0); //從A（100,0）開始context.lineTo(0, height); //從A(100,0)開始，畫到B (0,173)結束context.lineTo(200, height); //B(0,173)-C(200,173)context.lineTo(100, 0)context.stroke()
三角形就是三個座標點連線文字

空心字型

ctx.font="30px Arial";ctx.fillText("Hello World",10,50);

實心字型

ctx.font="30px Arial";ctx.strokeText("Hello World",10,50);
太極圖 
function drawTaiji() {        var x = 400        var y = 300        var r = 100        var x1 = x        var y1 = y - r / 2        var r1 = r / 2        var x2 = x        var y2 = y + r / 2        var r2 = r / 2        var xx1 = x        var yy1 = y - r / 2        var rr1 = r / 8        var xx2 = x        var yy2 = y + r / 2        var rr2 = r / 8        context.save()        context.beginPath()        context.fillStyle = "#000"        context.strokeStyle = "#000"        context.arc(x, y, r, -Math.PI * 0.5, Math.PI * 0.5)        context.fill()        context.stroke()        context.closePath()        context.restore()        context.save()        context.beginPath()        context.fillStyle = "#fff"        context.strokeStyle = "#000"        context.arc(x, y, r, -Math.PI * 0.5, Math.PI * 0.5, true)        context.fill()        context.stroke()        context.closePath()        context.restore()        context.save()        context.beginPath()        context.fillStyle = "#fff"        context.arc(x1, y1, r1, -Math.PI * 0.5, Math.PI * 0.5)        context.fill()        context.stroke()        context.closePath()        context.restore()        context.save()        context.beginPath()        context.fillStyle = "#000"        context.arc(x2, y2, r2, -Math.PI * 0.5, Math.PI * 0.5, true)        context.fill()        context.closePath()        context.restore()        context.save()        context.beginPath()        context.fillStyle = "#000"        context.arc(xx1, yy1, rr1, 0, Math.PI * 2)        context.fill()        context.closePath()        context.restore()        context.save()        context.beginPath()        context.fillStyle = "#fff"        context.arc(xx2, yy2, rr2, 0, Math.PI * 2)        context.fill()        context.closePath()        context.restore()}
以上效果圖旋轉太極圖
<canvas id="canvas" style="background-color: beige;border:1px solid #000;"></canvas><script>  canvasWidth = 800  canvasHeight = 600  var canvas = document.getElementById("canvas")  var context = canvas.getContext("2d")  canvas.width = canvasWidth  canvas.height = canvasHeight  // 太極  var x = 400  var y = 300  var r = 10  temp = 2 * Math.PI / 360  var angle = 0  var isAdd = true  setInterval(function () {    context.clearRect(0, 0, canvas.width, canvas.height)    drawTaiji(angle)    angle = angle + 11    if (isAdd) {   	 r = r + 10    } else {    	r = r - 10    }    console.log(angle)    if (angle >= 360) {    angle = 0    }    if (r >= 400) {    // r = 10     isAdd = false    } else if (r < 30) {      isAdd = true    }  }, 120)  function drawTaiji(angle) {    var x1 = x    var y1 = y - r / 2    var _rotateXY1 = getRotateXY("1", angle, x, y, r) // 1:x1,y1    if (_rotateXY1) {      x1 = _rotateXY1.x      y1 = _rotateXY1.y    }    var r1 = r / 2    var x2 = x    var y2 = y + r / 2    var _rotateXY2 = getRotateXY("2", angle, x, y, r) // 2:x2,y2    if (_rotateXY2) {      x2 = _rotateXY2.x      y2 = _rotateXY2.y    }    var r2 = r / 2    var xx1 = x1    var yy1 = y1    var rr1 = r / 8    var xx2 = x2    var yy2 = y2    var rr2 = r / 8    context.clearRect(x, y, r, r)    context.save()    context.beginPath()    context.fillStyle = "#000"    context.strokeStyle = "#00"    context.arc(x, y, r, -Math.PI * 0.5 + getAnimAngle(angle), Math.PI * 0.5 + getAnimAngle(angle))    context.fill()    context.closePath()    context.stroke()    context.restore()    context.save()    context.beginPath()    context.fillStyle = "#fff"    context.strokeStyle = "#fff"    context.arc(x, y, r, -Math.PI * 0.5 + getAnimAngle(angle), Math.PI * 0.5 + getAnimAngle(angle), true)    context.fill()    context.closePath()    context.stroke()    context.restore()    context.save()    context.beginPath()    context.fillStyle = "#fff"    context.strokeStyle = "#fff"    context.lineWidth = 0    context.arc(x1, y1, r1, -Math.PI * 0.5 + getAnimAngle(angle), Math.PI * 0.5 + getAnimAngle(angle + 90))    context.fill()    context.closePath()    context.restore()    context.save()    context.beginPath()    context.fillStyle = "#000"    context.strokeStyle = "#000"    context.lineWidth = 0    context.arc(x2, y2, r2, -Math.PI * 0.5 + getAnimAngle(angle + 90), Math.PI * 0.5 + getAnimAngle(angle), true)    context.fill()    context.closePath()    context.restore()    context.save()    context.beginPath()    context.fillStyle = "#000"    context.arc(xx1, yy1, rr1, 0, Math.PI * 2)    context.fill()    context.closePath()    context.restore()    context.save()    context.beginPath()    context.fillStyle = "#fff"    context.arc(xx2, yy2, rr2, 0, Math.PI * 2)    context.fill()    context.closePath()    context.restore()  }	function getRotateXY(type, angle, x, y, r) {    if (type == "1") {      return getRotateXY1(angle, x, y, r)    } else if (type == "2") {      return getRotateXY2(angle, x, y, r)    }  }  function getRotateXY2(angle, x, y, r) {    rt = r / 2    if (angle > 0 && angle < 90) {      angleTemp = angle      xt = Math.sin(angleTemp * temp) * rt      yt = Math.cos(angleTemp * temp) * rt      return { x: x - xt, y: y + yt }    } else if (angle > 90 && angle < 180) {      angleTemp = angle - 90      xt = Math.cos(angleTemp * temp) * rt      yt = Math.sin(angleTemp * temp) * rt      return { x: x - xt, y: y - yt }    } else if (angle > 180 && angle < 270) {      angleTemp = angle - 180      xt = Math.sin(angleTemp * temp) * rt      yt = Math.cos(angleTemp * temp) * rt      return { x: x + xt, y: y - yt }    } else if (angle > 270 && angle < 360) {      angleTemp = angle - 270      xt = Math.cos(angleTemp * temp) * rt      yt = Math.sin(angleTemp * temp) * rt      return { x: x + xt, y: y + yt }    } else {    	return null    }  }  function getRotateXY1(angle, x, y, r) {    rt = r / 2    if (angle > 0 && angle < 90) {      angleTemp = angle      xt = Math.sin(angleTemp * temp) * rt      yt = Math.cos(angleTemp * temp) * rt      return { x: x + xt, y: y - yt }    } else if (angle > 90 && angle < 180) {      angleTemp = angle - 90      xt = Math.cos(angleTemp * temp) * rt      yt = Math.sin(angleTemp * temp) * rt      return { x: x + xt, y: y + yt }    } else if (angle > 180 && angle < 270) {      angleTemp = angle - 180      xt = Math.sin(angleTemp * temp) * rt      yt = Math.cos(angleTemp * temp) * rt      return { x: x - xt, y: y + yt }    } else if (angle > 270 && angle < 360) {      angleTemp = angle - 270      xt = Math.cos(angleTemp * temp) * rt      yt = Math.sin(angleTemp * temp) * rt      return { x: x - xt, y: y - yt }    } else {      return null    }  }  function getAnimAngle(angle) {  	return temp * angle  }</script>
效果畫圖板（綜合事例）效果程式碼地址

https://github.com/jinshw/canvas

其中drawboard.html

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