我们接着上文[js高手之路] html5 canvas系列教程 - 认识canvas以及基本使用方法继续.
一、直线的绘制
cxt.moveTo( x1, y1 )： 将画笔移动到x1, y1这个点
cxt.lineTo( x2, y2 )：将画笔从起点开始画直线，一直画到终点坐标( x2, y2 )
cxt.stroke();用画笔连线，moveTo,lineTo并不会产生实际的线条
x1,y1,x2,y2是点的坐标，canvas的坐标原点在canvas的左上角.
画一根直线:
<style>
body {
background:#000;
}
#canvas {
background:white;
}
</style>
<script>
window.onload = function(){
var oCanvas = document.querySelector( "#canvas" ),
oGc = oCanvas.getContext( '2d' );
oGc.moveTo( 50, 50 );
oGc.lineTo( 250, 50 );
oGc.stroke();
}
</script>
</head>
<body>
<canvas id="canvas"></canvas>
</body>
如果把stroke注释了，是不会出现线条的，stoke的作用就是用来将点连起来
通过2个实例来区分，moveTo与lineTo的区别
<style>
body {
background:#000;
}
#canvas {
background:white;
}
</style>
<script>
window.onload = function(){
var oCanvas = document.querySelector( "#canvas" ),
oGc = oCanvas.getContext( '2d' );
oGc.moveTo( 50, 50 );
oGc.lineTo( 250, 50 );
oGc.moveTo( 50, 200 );
oGc.lineTo( 250, 200 );
oGc.stroke(); oGc.moveTo( 300, 50 );
oGc.lineTo( 500, 50 );
oGc.lineTo( 300, 200 );
oGc.lineTo( 500, 200 );
oGc.stroke();
}
</script>
</head>
<body>
<canvas id="canvas" width="600" height="400"></canvas>
</body>
左右两边的线形图，代码就一点区别，左边图形是第二个点用了lineTo, 第三个点用了moveTo, 右边图形第二个点用了lineTo，第三个点还是lineTo，从图中你应该能感受到这两个方法的区别吧？
画三角形
<style>
body {
background:#000;
}
#canvas {
background:white;
}
</style>
<script>
window.onload = function(){
var oCanvas = document.querySelector( "#canvas" ),
oGc = oCanvas.getContext( '2d' ); oGc.moveTo( 50, 50 );
oGc.lineTo( 450, 50 );
oGc.lineTo( 450, 300 );
oGc.lineTo( 50, 50 );
oGc.stroke();
}
</script>
</head>
<body>
<canvas id="canvas" width="600" height="400"></canvas>
</body>
把上面的代码，稍微修改下，就能画出一个矩形了
<style>
body {
background:#000;
}
#canvas {
background:white;
}
</style>
<script>
window.onload = function(){
var oCanvas = document.querySelector( "#canvas" ),
oGc = oCanvas.getContext( '2d' ); oGc.moveTo( 50, 50 );
oGc.lineTo( 450, 50 );
oGc.lineTo( 450, 300 );
oGc.lineTo( 50, 300 );
oGc.lineTo( 50, 50 );
oGc.stroke();
}
</script>
</head>
<body>
<canvas id="canvas" width="600" height="400"></canvas>
</body>
二，canvas提供了画矩形的API
通过线条我们也能拼接出一个矩形，但是代码太多，每个点都要把握，显得比较麻烦，canvas为我们提供了画矩形的API，有两种，一种是描边矩形，一种是填充矩形.
cxt.strokeStyle = 属性值
cxt.strokeRect( x, y, width, height )
strokeStyle后面的属性是为了修饰线条的，主要包括( 颜色值，渐变色，图案 ），颜色支持英文单词，十六进制，RGB, RGBA格式的颜色设置.
strokeRect: x, y为矩形的左上角坐标，width和height为矩形的宽度和高度
<script>
window.onload = function(){
var oCanvas = document.querySelector( "#canvas" ),
oGc = oCanvas.getContext( '2d' ); oGc.strokeStyle = '#09f';
oGc.strokeRect( 50, 50, 500, 300 );
}
</script>
</head>
<body>
<canvas id="canvas" width="600" height="400"></canvas>
</body>
注意：oGc.strokeStyle = '#09f'; 如果把这句代码放在oGc.strokeRect( 50, 50, 500, 300 );的后面，那么设置的线条样式将不会生效，strokeStyle一定要在画图之前设置，否则是不会应用到的
填充矩形API
cxt.fillStyle = 属性值;
cxt.fillRect( x, y, width, height );
跟上面是一样的，只是把stoke换成了fill，fill就是填充的意思
画一个带有透明度的矩形：
<script>
window.onload = function(){
var oCanvas = document.querySelector( "#canvas" ),
oGc = oCanvas.getContext( '2d' ); oGc.fillStyle = 'rgba( 255, 0, 0, 0.3 )';
oGc.fillRect( 50, 50, 500, 300 );
}
</script>
</head>
<body>
<canvas id="canvas" width="600" height="400"></canvas>
</body>
另一种绘制矩形的API：cxt.rect( x, y, width, height );
他与strokeRect和fillRect有什么区别呢？
1，共同点：参数的意思相同
2，不同点，调用strokeRect和fillRect会立即绘制出矩形，而rect并不会，他需要调用stoke()或者fill()方法，才能把矩形绘制出来
<script>
window.onload = function(){
var oCanvas = document.querySelector( "#canvas" ),
oGc = oCanvas.getContext( '2d' ); oGc.fillStyle = 'rgba( 255, 0, 0, 0.3 )';
oGc.rect( 50, 50, 500, 300 );
// oGc.stroke();
oGc.fill();
}
</script>
</head>
<body>
<canvas id="canvas" width="600" height="400"></canvas>
</body>
清空矩形API：cxt.clearRect( x, y, width, height ); 参数跟strokeRect,fillRect意思一样
<script>
window.onload = function(){
var oCanvas = document.querySelector( "#canvas" ),
oGc = oCanvas.getContext( '2d' ); oGc.fillStyle = 'rgba( 255, 0, 0, 0.3 )';
oGc.fillRect( 50, 50, 500, 300 ); oGc.clearRect( 100, 100, 200, 200 );
}
</script>
</head>
<body>
<canvas id="canvas" width="600" height="400"></canvas>
</body>
用fillRect和clearRect画一个加号，当然你可以用moveTo和lineTo,不过代码应该比这种方法多了不少.
<script>
window.onload = function(){
var oCanvas = document.querySelector( "#canvas" ),
oGc = oCanvas.getContext( '2d' ); oGc.fillStyle = 'rgba( 255, 0, 0, 0.3 )';
oGc.fillRect( 100, 100, 200, 200 );
oGc.clearRect( 100, 100, 50, 50 );
oGc.clearRect( 250, 100, 50, 50 );
oGc.clearRect( 250, 250, 50, 50 );
oGc.clearRect( 100, 250, 50, 50 );
}
</script>
</head>
<body>
<canvas id="canvas" width="400" height="400"></canvas>
</body>
绘制一个调色板：
<style>
body {
background:#000;
}
#canvas {
background:white;
}
</style>
<script>
window.onload = function(){
var oCanvas = document.querySelector( "#canvas" ),
oGc = oCanvas.getContext( '2d' ),
aColor = [ '00', '33', '66', '99', 'cc', 'ff' ],
aMiddle = [ 'ff', 'cc', '99', '66', '33', '00' ], count = 0;
for( var i = 0; i < 12; i++ ){
for( var j = 0; j < 18; j++ ){
count++;
if ( i < 6 && count < 6 && j < 6 )
oGc.fillStyle = `#${aColor[i]}${aMiddle[0]}${aColor[j]}`;
else if( i < 6 && count < 12 && j < 12 )
oGc.fillStyle = `#${aColor[i]}${aMiddle[1]}${aColor[j-6]}`;
else if ( i < 6 && count < 18 && j < 18 )
oGc.fillStyle = `#${aColor[i]}${aMiddle[2]}${aColor[j-12]}`;
else if ( count < 6 && j < 6 )
oGc.fillStyle = `#${aColor[i-6]}${aMiddle[3]}${aColor[j]}`;
else if ( count < 12 && j < 12 )
oGc.fillStyle = `#${aColor[i-6]}${aMiddle[4]}${aColor[j-6]}`;
else if ( count < 18 && j < 18 )
oGc.fillStyle = `#${aColor[i-6]}${aMiddle[5]}${aColor[j-12]}`;
oGc.fillRect( j * 40, i * 40, 40, 40 );
}
count = 0;
}
}
</script>
</head>
<body>
<canvas id="canvas" width="720" height="720"></canvas>
</body>
javascript原生实现调色板：
var aColor = [ '00', '33', '66', '99', 'cc', 'ff' ],
aMiddle = [ 'ff', 'cc', '99', '66', '33','00' ]; document.write( "<table>" );
for( var i = 0; i < 12; i++ ){
document.write( "<tr>" );
for( var j = 0 ; j < 18; j++ ) {
if ( i < 6 && j < 6 ) //前6行,左6列
document.write( "<td style='background-color:#" + aColor[i]+ aMiddle[0] + aColor[j] + "'> </td>" );
else if ( i < 6 && j < 12 ){ //前6行 中间6列
document.write( "<td style='background-color:#" + aColor[i]+ aMiddle[1] + aColor[j-6] + "'> </td>" );
}else if ( i < 6 && j < 18 ){ //前6行, 后面6列
document.write( "<td style='background-color:#" + aColor[i]+ aMiddle[2] + aColor[j-12] + "'> </td>" );
}else if ( i < 12 && j < 6 ){ //后6行, 左6列
document.write( "<td style='background-color:#" + aColor[i-6]+ aMiddle[3] + aColor[j] + "'> </td>" );
}else if ( i < 12 && j < 12 ){ //后6行, 中6列
document.write( "<td style='background-color:#" + aColor[i-6]+ aMiddle[4] + aColor[j-6] + "'> </td>" );
}else if ( i < 12 && j < 18 ){ //后6行, 后6列
document.write( "<td style='background-color:#" + aColor[i-6]+ aMiddle[5] + aColor[j-12] + "'> </td>" );
}
}
document.write( "</tr>" );
}
document.write( "</table>" );