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话不多说，请看代码
<!DOCTYPE html ">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
<script type="text/javascript">
function draw21(id) {
var canvas = document.getElementById(id)
if (canvas == null)
return false;
var context = canvas.getContext("2d");
//实践表明在不设施fillStyle下的默认fillStyle=black
context.fillRect(0, 0, 100, 100);
//实践表明在不设施strokeStyle下的默认strokeStyle=black
context.strokeRect(120, 0, 100, 100);
//设置纯色
context.fillStyle = "red";
context.strokeStyle = "blue";
context.fillRect(0, 120, 100, 100);
context.strokeRect(120, 120, 100, 100);
//设置透明度实践证明透明度值>0,<1值越低，越透明，值>=1时为纯色，值<=0时为完全透明
context.fillStyle = "rgba(255,0,0,0.2)";
context.strokeStyle = "rgba(255,0,0,0.2)";
context.fillRect(240,0 , 100, 100);
context.strokeRect(240, 120, 100, 100);
}
function draw22(id) {
var canvas = document.getElementById(id)
if (canvas == null)
return false;
var context = canvas.getContext("2d");
//实践表明在不设施fillStyle下的默认fillStyle=black
context.fillRect(0, 0, 100, 100);
//实践表明在不设施strokeStyle下的默认strokeStyle=black
context.strokeRect(120, 0, 100, 100);
//设置纯色
context.fillStyle = "red";
context.strokeStyle = "blue";
context.fillRect(0, 120, 100, 100);
context.strokeRect(120, 120, 100, 100);
//设置透明度实践证明透明度值>0,<1值越低，越透明，值>=1时为纯色，值<=0时为完全透明
context.fillStyle = "rgba(255,0,0,0.2)";
context.strokeStyle = "rgba(255,0,0,0.2)";
context.fillRect(240, 0, 100, 100);
context.strokeRect(240, 120, 100, 100);
context.clearRect(50, 50, 240, 120);
}
function draw23(id) {
var canvas = document.getElementById(id);
if (canvas == null) {
return false;
}
var context = canvas.getContext('2d');
var n = 0;
//左侧1/4圆弧
context.beginPath();
context.arc(100, 150, 50, 0, Math.PI/2 , false);
context.fillStyle = 'rgba(255,0,0,0.25)';
context.fill();
context.strokeStyle = 'rgba(255,0,0,0.25)'
context.closePath();
context.stroke();
//右侧1/4圆弧
context.beginPath();
context.arc(300, 150, 50, 0, Math.PI/2 , false);
context.fillStyle = 'rgba(255,0,0,0.25)';
context.fill();
context.strokeStyle = 'rgba(255,0,0,0.25)';
context.closePath();
context.stroke();
}
function draw0(id) {
var canvas = document.getElementById(id);
if (canvas == null) {
return false;
}
var context = canvas.getContext('2d');
context.beginPath();
context.arc(200, 150, 100, 0, Math.PI * 2, true);
//不关闭路径路径会一直保留下去，当然也可以利用这个特点做出意想不到的效果
context.closePath();
context.fillStyle = 'rgba(0,255,0,0.25)';
context.fill();
}
function draw1(id) {
var canvas = document.getElementById(id);
if (canvas == null)
return false;
var context = canvas.getContext("2d");
context.fillStyle = "#EEEEFF";
context.fillRect(0, 0, 400, 300);
var n = 0;
var dx = 150;
var dy = 150;
var s = 100;
context.beginPath();
context.fillStyle = 'rgb(100,255,100)';
context.strokeStyle = 'rgb(0,0,100)';
var x = Math.sin(0);
var y = Math.cos(0);
var dig = Math.PI / 15 * 11;
for (var i = 0; i < 30; i++) {
var x = Math.sin(i * dig);
var y = Math.cos(i * dig);
context.lineTo(dx + x * s, dy + y * s);
}
context.closePath();
context.fill();
context.stroke();
}
function draw2(id) {
var canvas = document.getElementById(id);
if (canvas == null) {
return false;
}
var context = canvas.getContext("2d");
context.fillStyle = "#EEEFF";
context.fillRect(0, 0, 400, 300);
var n = 0;
var dx = 150;
var dy = 150;
var s = 100;
context.beginPath();
context.globalCompositeOperation = 'and';
context.fillStyle = 'rgb(100,255,100)';
var x = Math.sin(0);
var y = Math.cos(0);
var dig = Math.PI / 15 * 11;
context.moveTo(dx, dy);
for (var i = 0; i < 30; i++) {
var x = Math.sin(i * dig);
var y = Math.cos(i * dig);
context.bezierCurveTo(dx + x * s, dy + y * s - 100, dx + x * s + 100, dy + y * s, dx + x * s, dy + y * s);
}
context.closePath();
context.fill();
context.stroke();
}
function draw24(id) {
var canvas = document.getElementById(id);
if (canvas == null) {
return false;
}
var context = canvas.getContext("2d");
context.moveTo(50, 50);
context.bezierCurveTo(50, 50,150, 50, 150, 150);
context.stroke();
context.quadraticCurveTo(150, 250, 250, 250);
context.stroke();
}
function draw25(id) {
var canvas = document.getElementById(id);
if (canvas == null)
return false;
var context = canvas.getContext('2d');
var g1 = context.createLinearGradient(0, 0, 0, 300);
g1.addColorStop(0, 'rgb(255,0,0)'); //红
g1.addColorStop(0.5, 'rgb(0,255,0)');//绿
g1.addColorStop(1, 'rgb(0,0,255)'); //蓝
//可以把lg对象理解成GDI中线性brush
context.fillStyle = g1;
//再用这个brush来画正方形
context.fillRect(0, 0, 400, 300);
}
function draw3(id) {
var canvas = document.getElementById(id);
if (canvas == null)
return false;
var context = canvas.getContext('2d');
var g1 = context.createLinearGradient(0, 0, 0, 300);
g1.addColorStop(0,'rgb(255,255,0)');//浅绿
g1.addColorStop(1,'rgb(0,255,255)');//浅蓝
context.fillStyle = g1;
context.fillRect(0, 0, 400, 300);
var n = 0;
var g2 = context.createLinearGradient(0, 0, 300, 0);
g2.addColorStop(0, 'rgba(0,0,255,0.5)');//蓝色
g2.addColorStop(1, 'rgba(255,0,0,0.5)');//红色
for (var i = 0; i < 10; i++) {
context.beginPath();
context.fillStyle = g2;
context.arc(i * 25, i * 25, i * 10, 0, Math.PI * 2, true);
context.closePath();
context.fill();
}
}
function draw26(id) {
//同一个圆心画球型
/*var canvas = document.getElementById(id);
if (canvas == null)
return false;
var context = canvas.getContext('2d');
var g1 = context.createRadialGradient(200, 150, 0, 200, 150, 100);
g1.addColorStop(0.1, 'rgb(255,0,0)');
g1.addColorStop(1, 'rgb(50,0,0)');
context.fillStyle = g1;
context.beginPath();
context.arc(200, 150, 100, 0, Math.PI * 2, true);
context.closePath();
context.fill();*/
//不同圆心看径向渐变模型
var canvas = document.getElementById(id);
if (canvas == null)
return false;
var context = canvas.getContext('2d');
var g1 = context.createRadialGradient(100, 150, 10, 300, 150, 50);
g1.addColorStop(0.1, 'rgb(255,0,0)');
g1.addColorStop(0.5, 'rgb(0,255,0)');
g1.addColorStop(1, 'rgb(0,0,255)');
context.fillStyle = g1;
context.fillRect(0, 0, 400, 300);
}
function draw27(id) {
var canvas = document.getElementById(id);
if (canvas == null)
return false;
var context = canvas.getContext('2d');
context.shadowOffsetX = 10;
context.shadowOffsetY = 10;
context.shadowColor = 'rgba(100,100,100,0.5)';
context.shadowBlur = 1.5;