1)用路径绘图:
beginPath()——开始一条新路径;
closePath()——尝试闭合现有路径,方法是绘制一条线,连接最后那条线的终点与初始坐标;
fill()——填充用子路径描述的图形;
isPointInPath(x,y)——如果指定的点在当前路径所描述的图形之内则返回true;
lineTo(x,y)——绘制一条到指定坐标的子路径;
moveTo(x,y)——移动到指定坐标而不绘制子路径;
rect(x,y,w,h)——绘制一个矩形,其左上角位于(x,y),宽度是w,高度是h;
stroke()——给子路径描述的图形绘制轮廓线;
<style type="text/css"> canvas{ border:thin solid black; margin: 4px; } body > *{ float: left; } </style>
<canvas id="canvas1" width="500" height="140"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> //由直线创建路径 var ctx=document.getElementById("canvas1").getContext("2d"); ctx.fillStyle="#136455"; ctx.strokeStyle="blue"; ctx.lineWidth=4; ctx.beginPath(); ctx.moveTo(10,10); ctx.lineTo(110,10); ctx.lineTo(110,120); ctx.closePath(); ctx.fill(); ctx.beginPath(); ctx.moveTo(150,10); ctx.lineTo(200,10); ctx.lineTo(200,120); ctx.lineTo(190,120); ctx.fill(); ctx.stroke(); ctx.beginPath(); ctx.moveTo(250,10); ctx.lineTo(250,120); ctx.stroke(); </script>
lineCap——在绘制线条或闭合图形时设置线条末端的样式;
<canvas id="canvas2" width="500" height="140"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> //设置lineCap属性 var ctx2=document.getElementById("canvas2").getContext("2d"); ctx2.strokeStyle="red"; ctx2.lineWidth=2; ctx2.beginPath(); ctx2.moveTo(0,50); ctx2.lineTo(200,50); ctx2.stroke(); ctx2.strokeStyle="black"; ctx2.lineWidth=40; var xpos=50; var styles=["butt","round","square"]; for(var i=0;i<styles.length;i++){ ctx2.beginPath(); ctx2.lineCap=styles[i]; ctx2.moveTo(xpos,50); ctx2.lineTo(xpos,150); ctx2.stroke(); xpos+=50; } </script>
<canvas id="canvas3" width="500" height="140"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> //用Rect方法绘制矩形 var ctx3=document.getElementById("canvas3").getContext("2d"); ctx3.fillStyle="yellow"; ctx3.strokeStyle="black"; ctx3.lineWidth=4; ctx3.beginPath(); ctx3.moveTo(110,10); ctx3.lineTo(110,100); ctx3.lineTo(10,10); ctx3.closePath(); ctx3.rect(110,10,100,90); ctx3.rect(110,100,130,30); ctx3.fill(); ctx3.stroke(); </script>
2)绘制圆弧:
arc(x,y,rad,startAngle,endAngle,direction)——绘制一段圆弧到(x,y),半径为rad,起始角度为 startAngle,结束角度为endAngle。可选参数direction指定了圆弧的方向;
arcTo(x1,y1,x2,y2,rad)——绘制一段半径为rad,经过(x1,y1),直到(x2,y2)的圆弧;
<canvas id="canvas4" width="500" height="140"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> //使用arcTo方法 var ctx4=document.getElementById("canvas4").getContext("2d"); var point1=[100,10]; var point2=[200,10]; var point3=[200,110]; ctx4.fillStyle="yellow"; ctx4.strokeStyle="black"; ctx4.lineWidth=4; ctx4.beginPath(); ctx4.moveTo(point1[0],point1[1]); ctx4.arcTo(point2[0],point2[1],point3[0],point3[1],100); ctx4.stroke(); drawPoint(point1[0],point1[1]); drawPoint(point2[0],point2[1]); drawPoint(point3[0],point3[1]); ctx4.beginPath(); ctx4.moveTo(point1[0],point1[1]); ctx4.lineTo(point2[0],point2[1]); ctx4.lineTo(point3[0],point3[1]); ctx4.stroke(); function drawPoint(x,y){ ctx4.lineWidth=1; ctx4.strokeStyle="red"; ctx4.strokeRect(x-2,y-2,4,4); } </script>
<canvas id="canvas5" width="500" height="140"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> //响应鼠标移动绘制圆弧 var canvasElem = document.getElementById("canvas5"); var ctx5 = canvasElem.getContext("2d"); var point1 = [100, 10]; var point2 = [200, 10]; var point3 = [200, 110]; draw(); canvasElem.onmousemove = function (e) { if (e.ctrlKey) { point1 = [e.clientX, e.clientY]; } else if(e.shiftKey) { point2 = [e.clientX, e.clientY]; } else { point3 = [e.clientX, e.clientY]; } ctx5.clearRect(0, 0, 540, 140); draw(); } function draw() { ctx5.fillStyle = "yellow"; ctx5.strokeStyle = "black"; ctx5.lineWidth = 4; ctx5.beginPath(); ctx5.moveTo(point1[0], point1[1]); ctx5.arcTo(point2[0], point2[1], point3[0], point3[1], 50); ctx5.stroke(); drawPoint(point1[0], point1[1]); drawPoint(point2[0], point2[1]); drawPoint(point3[0], point3[1]); ctx5.beginPath(); ctx5.moveTo(point1[0], point1[1]); ctx5.lineTo(point2[0], point2[1]); ctx5.lineTo(point3[0], point3[1]); ctx5.stroke(); } function drawPoint(x, y) { ctx5.lineWidth = 1; ctx5.strokeStyle = "red"; ctx5.strokeRect(x -2, y-2, 4, 4); } </script>
<canvas id="canvas6" width="500" height="140"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> //使用arc方法 var ctx6=document.getElementById("canvas6").getContext("2d"); ctx6.fillStyle="yellow"; ctx6.lineWidth=3; ctx6.beginPath(); ctx6.arc(70,70,60,0,Math.PI,true); ctx6.stroke(); ctx6.beginPath(); ctx6.arc(200,70,60,Math.PI/2,Math.PI/4,false); ctx6.fill(); ctx6.stroke(); ctx6.beginPath(); var val=0; for(var i=0;i<4;i++){ ctx6.arc(350,70,60,val,val+Math.PI/4,false); val+=Math.PI/2; } ctx6.closePath(); ctx6.fill(); ctx6.stroke(); </script>
3)绘制贝塞尔曲线
bezierCurveTo(cx1,cy1,cx2,cy2,x,y)——绘制一段贝塞尔曲线到点(x,y),控制点为(cx1,cy1)和(cx2,cy2);
quadraticCurveTo(cx,xy,x,y)——绘制一段二次贝塞尔曲线到点(x,y),控制点为(cx,cy);
<canvas id="canvas" width="500" height="140"> Your browser doesn't support the <code>canvas</code> element </canvas>
<script> var canvasElem = document.getElementById("canvas"); var ctx = canvasElem.getContext("2d"); var startPoint = [50, 100]; var endPoint = [400, 100]; var cp1 = [250, 50]; var cp2 = [350, 50]; canvasElem.onmousemove = function(e) { if (e.shiftKey) { cp1 = [e.clientX, e.clientY]; } else if (e.ctrlKey) { cp2 = [e.clientX, e.clientY]; } ctx.clearRect(0, 0, 500, 140); draw(); } draw(); function draw() { ctx.lineWidth = 3; ctx.strokeStyle = "black"; ctx.beginPath(); ctx.moveTo(startPoint[0], startPoint[1]); ctx.bezierCurveTo(cp1[0], cp1[1], cp2[0], cp2[1], endPoint[0], endPoint[1]); ctx.stroke(); ctx.lineWidth = 1; ctx.strokeStyle = "red"; var points = [startPoint, endPoint, cp1, cp2]; for (var i = 0; i < points.length; i++) { drawPoint(points[i]); } drawLine(startPoint, cp1); drawLine(endPoint, cp2); } function drawPoint(point) { ctx.beginPath(); ctx.strokeRect(point[0] -2, point[1] -2, 4, 4); } function drawLine(from, to) { ctx.beginPath(); ctx.moveTo(from[0], from[1]); ctx.lineTo(to[0], to[1]); ctx.stroke(); } </script>
<canvas id="canvas" width="500" height="140"> Your browser doesn't support the <code>canvas</code> element </canvas>
<script> //绘制二次贝塞尔曲线 var canvasElem = document.getElementById("canvas"); var ctx = canvasElem.getContext("2d"); var startPoint = [50, 100]; var endPoint = [400, 100]; var cp1 = [250, 50]; canvasElem.onmousemove = function(e) { if (e.shiftKey) { cp1 = [e.clientX, e.clientY]; } ctx.clearRect(0, 0, 500, 140); draw(); } draw(); function draw() { ctx.lineWidth = 3; ctx.strokeStyle = "black"; ctx.beginPath(); ctx.moveTo(startPoint[0], startPoint[1]); ctx.quadraticCurveTo(cp1[0], cp1[1], endPoint[0], endPoint[1]); ctx.stroke(); ctx.lineWidth = 1; ctx.strokeStyle = "red"; var points = [startPoint, endPoint, cp1]; for (var i = 0; i < points.length; i++) { drawPoint(points[i]); } drawLine(startPoint, cp1); drawLine(endPoint, cp1); } function drawPoint(point) { ctx.beginPath(); ctx.strokeRect(point[0] -2, point[1] -2, 4, 4); } function drawLine(from, to) { ctx.beginPath(); ctx.moveTo(from[0], from[1]); ctx.lineTo(to[0], to[1]); ctx.stroke(); } </script>
4)创建剪辑区域
clip()——创建新的裁剪区域;
<canvas id="canvas7" width="500" height="140"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> var ctx7=document.getElementById("canvas7").getContext("2d"); ctx7.fillStyle="yellow"; ctx7.beginPath(); ctx7.rect(0,0,500,140); ctx7.fill(); ctx7.beginPath(); ctx7.rect(100,20,300,100); ctx7.clip(); ctx7.fillStyle="red"; ctx7.beginPath(); ctx7.rect(0,0,500,140); ctx7.fill(); </script>
5)绘制文本:
fillText(
strokeText(
font——设置绘制文本时使用的字体;
textAlign——设置文本的对齐方式:start、end、left、right、center;
textBaseline——设置文本的基线:top、hanging、middle、alphabetic、ideographic、bottom;
6)使用特效和转换:
6.1)使用阴影:
shadowBlur——设置阴影的模糊程度;
shadowColor——设置阴影的颜色;
shadowOffsetX——设置阴影的水平偏移量;
shadowOffsetY——设置阴影的垂直偏移量;
<canvas id="canvas8" width="500" height="140"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> //给图形和文本应用阴影 var ctx8=document.getElementById("canvas8").getContext("2d"); ctx8.fillStyle="lightgrey"; ctx8.strokeStyle="black"; ctx8.lineWidth=3; ctx8.shadowOffsetX=5; ctx8.shadowOffsetY=5; ctx8.shadowBlur=5; ctx8.shadowColor="grey"; ctx8.beginPath(); ctx8.arc(420,70,50,0,Math.PI,true); ctx8.stroke(); ctx8.beginPath(); ctx8.arc(420,80,40,0,Math.PI,false); ctx8.fill(); ctx8.font="100px sans-serif"; ctx8.fillText("hello",50,100); ctx8.strokeText("hello",50,100); </script>
6.2)使用透明度:
globalAlpha——给文本和图形设置透明度(从0到1);
<canvas id="canvas9" width="300" height="120"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> //使用globalAlpha属性,设置透明度 var ctx9=document.getElementById("canvas9").getContext("2d"); ctx9.fillStyle="lightgrey"; ctx9.strokeStyle="black"; ctx9.lineWidth=3; ctx9.font="100px sans-serif"; ctx9.fillText("hello",10,100); ctx9.strokeText("hello",10,100); ctx9.fillStyle="red"; ctx9.globalAlpha=0.5; ctx9.fillRect(10,10,240,100); </script>
6.3)使用合成:
globalCompositeOperation——与透明度属性结合使用,来控制图形和文本在画布上绘制的方式;
globalCompositeOperation允许的值:
=copy——将来源绘制于目标之上,忽略一切透明度设置;
=source-atop——在两个图像都不透明处显示来源图像,
目标图像不透明但来源图像透明处显示目标图像,其它位置显示为透明;
=source-in——来源图像和目标图像都不透明处显示来源图像。其它位置显示为透明;
=source-out——来源图像不透明但目标图像透明处显示来源图像。其它位置显示为透明;
=source-over——来源图像不透明处显示来源图像。其它位置显示目标图像;
=destination-atop——与source-atop相同,但用目标图像替代来源图像,反之亦然;
=destination-in——与source-in相同,但用目标图像替代来源图像,反之亦然;
=destination-over——与source-over相同,但用目标图像替代来源图像,反之亦然;
=destination-out——与source-out相同,但用目标图像替代来源图像,反之亦然;
=lighter——显示来源图像与目标图像的总和,颜色值限制最高255(100%);
=xor——对来源图像和目标图像执行异或运算;
<canvas id="canvas10" width="300" height="120"> 您的浏览器不支持<code>canvas</code>! </canvas> <label>Comosition Value:</label> <select id="list"> <option>copy</option> <option>destination-atop</option> <option>destination-in</option> <option>destination-over</option> <option>destination-out</option> <option>lighter</option> <option>source-atop</option> <option>source-in</option> <option>source-out</option> <option>source-over</option> <option>xor</option> </select>
<script> //使用globalCompositeOperation属性 var ctx10=document.getElementById("canvas10").getContext("2d"); ctx10.fillStyle="lightgrey"; ctx10.strokeStyle="black"; ctx10.lineWidth=3; var compVal="copy"; document.getElementById("list").onchange=function(e){ compVal= e.target.value; draw(); } draw(); function draw(){ ctx10.clearRect(0,0,300,120); ctx10.globalAlpha=1.0; ctx10.font="100px sans-serif"; ctx10.fillText("hello",10,100); ctx10.strokeText("hello",10,100); ctx10.globalCompositeOperation=compVal; ctx10.fillStyle="red"; ctx10.globalAlpha=0.5; ctx10.fillRect(100,10,150,100); } </script>
6.4)使用变换:
scale(
rotate(
translate(
transform(a,b,c,d,e,f)——合并现有的变换和a-f值所指定的矩阵;
setTansform(a,b,c,d,e,f)——用a-f值所指定的矩阵替换现有的变换;
<canvas id="canvas11" width="400" height="200"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> //使用变换 var ctx11=document.getElementById("canvas11").getContext("2d"); ctx11.fillStyle="lightgrey"; ctx11.strokeStyle="black"; ctx11.lineWidth=3; ctx11.clearRect(0,0,300,120); ctx11.globalAlpha=1.0; ctx11.font="100px sans-serif"; ctx11.fillText("hello",10,100); ctx11.strokeText("hello",10,100); ctx11.scale(1.3,1.3); ctx11.translate(100,-50); ctx11.rotate(0.5); ctx11.fillStyle="red"; ctx11.globalAlpha=0.5; ctx11.fillRect(100,10,150,100); ctx11.strokeRect(0,0,300,200); </script>
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