Canvas Clock Hands
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Canvas Clock Hands
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Part IV - Draw Clock Hands
The clock needs hands. Create a JavaScript function to draw clock hands:
JavaScript:
function drawClock() {
drawFace(ctx, radius);
drawNumbers(ctx, radius);
drawTime(ctx, radius);
}
function drawTime(ctx, radius){
var now = new Date();
var hour = now.getHours();
var minute = now.getMinutes();
var second = now.getSeconds();
//hour
hour=hour%12;
hour=(hour*Math.PI/6)+(minute*Math.PI/(6*60))+(second*Math.PI/(360*60));
drawHand(ctx, hour, radius*0.5, radius*0.07);
//minute
minute=(minute*Math.PI/30)+(second*Math.PI/(30*60));
drawHand(ctx, minute, radius*0.8, radius*0.07);
// second
second=(second*Math.PI/30);
drawHand(ctx, second,
radius*0.9, radius*0.02);
}
function drawHand(ctx,
pos, length, width) {
ctx.beginPath();
ctx.lineWidth = width;
ctx.lineCap = "round";
ctx.moveTo(0,0);
ctx.rotate(pos);
ctx.lineTo(0, -length);
ctx.stroke();
ctx.rotate(-pos);
}
Try it Yourself »
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Example Explained
Use Date to get hour, minute, second:
var now = new Date();
var hour = now.getHours();
var minute = now.getMinutes();
var second = now.getSeconds();Calculate the angle of the hour hand, and draw it a length (50% of radius),
and a width (7% of radius):
hour=hour%12;
hour=(hour*Math.PI/6)+(minute*Math.PI/(6*60))+(second*Math.PI/(360*60));
drawHand(ctx, hour, radius*0.5, radius*0.07);Use the same technique for minutes and seconds.
The drawHand() routine does not need an explanation. It just draws a line
with a given length and width.
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var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var radius = canvas.height/2;
ctx.translate(radius, radius);
radius = radius*0.90
drawClock();
function drawClock() {
drawFace(ctx, radius);
drawNumbers(ctx, radius);
drawTime(ctx, radius);
}
