参考书目：《HTML5 Canvas核心技术 图形、动画与游戏开发》
将canvas的内容打印成图像—改写的时钟程序
1-11.html
Canvas not supported
.
1-12.js
var canvas = document.getElementById('canvas'),
context = canvas.getContext('2d'),
CLOCK_RADIUS = canvas.width/2 - 15,
HOUR_HAND_TRUNCATION = 35,
ballPainter = {
paint: function (sprite, context) {
var x = sprite.left + sprite.width/2,
y = sprite.top + sprite.height/2,
width = sprite.width,
height = sprite.height,
radius = sprite.width/2;
context.save();
context.beginPath();
context.arc(x, y, radius, 0, Math.PI*2, false);
context.clip();
context.shadowColor = 'rgb(0,0,0)';
context.shadowOffsetX = -4;
context.shadowOffsetY = -4;
context.shadowBlur = 8;
context.fillStyle = 'rgba(218, 165, 32, 0.1)';
context.fill();
context.lineWidth = 2;
context.strokeStyle = 'rgb(100,100,195)';
context.stroke();
context.restore();
}
},
ball = new Sprite('ball', ballPainter);
function drawGrid(color, stepx, stepy) {
context.save()
context.shadowColor = undefined;
context.shadowBlur = 0;
context.shadowOffsetX = 0;
context.shadowOffsetY = 0;
context.strokeStyle = color;
context.fillStyle = '#ffffff';
context.lineWidth = 0.5;
context.fillRect(0, 0, context.canvas.width, context.canvas.height);
for (var i = stepx + 0.5; i < context.canvas.width; i += stepx) {
context.beginPath();
context.moveTo(i, 0);
context.lineTo(i, context.canvas.height);
context.stroke();
}
for (var i = stepy + 0.5; i < context.canvas.height; i += stepy) {
context.beginPath();
context.moveTo(0, i);
context.lineTo(context.canvas.width, i);
context.stroke();
}
context.restore();
}
function drawHand(loc, isHour) {
var angle = (Math.PI*2) * (loc/60) - Math.PI/2,
handRadius = isHour ? CLOCK_RADIUS - HOUR_HAND_TRUNCATION
: CLOCK_RADIUS,
lineEnd = {
x: canvas.width/2 +
Math.cos(angle)*(handRadius - ball.width/2),
y: canvas.height/2 +
Math.sin(angle)*(handRadius - ball.width/2)
};
context.beginPath();
context.moveTo(canvas.width/2, canvas.height/2);
context.lineTo(lineEnd.x, lineEnd.y);
context.stroke();
ball.left = canvas.width/2 +
Math.cos(angle)*handRadius - ball.width/2;
ball.top = canvas.height/2 +
Math.sin(angle)*handRadius - ball.height/2;
ball.paint(context);
}
function drawClock() {
drawClockFace();
drawHands();
}
function drawHands() {
var date = new Date(),
hour = date.getHours();
ball.width = 20;
ball.height = 20;
drawHand(date.getSeconds(), false);
hour = hour > 12 ? hour - 12 : hour;
ball.width = 35;
ball.height = 35;
drawHand(date.getMinutes(), false);
ball.width = 50;
ball.height = 50;
drawHand(hour*5 + (date.getMinutes()/60)*5);
ball.width = 10;
ball.height = 10;
ball.left = canvas.width/2 - ball.width/2;
ball.top = canvas.height/2 - ball.height/2;
ballPainter.paint(ball, context);
}
function drawClockFace() {
context.beginPath();
context.arc(canvas.width/2, canvas.height/2,
CLOCK_RADIUS, 0, Math.PI*2, false);
context.save();
context.strokeStyle = 'rgba(0,0,0,0.2)';
context.stroke();
context.restore();
}
function animate() {
context.clearRect(0,0,canvas.width,canvas.height);
drawGrid('lightgray', 10, 10);
drawClock();
window.requestNextAnimationFrame(animate);
}
context.lineWidth = 0.5;
context.strokeStyle = 'rgba(0,0,0,0.2)';
if (navigator.userAgent.indexOf('Opera') === -1)
context.shadowColor = 'rgba(0,0,0,0.5)';
context.shadowOffsetX = 2;
context.shadowOffsetY = 2;
context.shadowBlur = 4;
context.stroke();
window.requestNextAnimationFrame(animate);
drawGrid('lightgray', 10, 10);
效果如图：