HTML 5 Canvas Speedometer
In this sample code, we will create a simple speedometer in HTML5 Canvas
HTML5 Canvas Speedometer
<!DOCTYPE html>
<html>
<head>
<style>
</style>
<script>
function redraw()
{
draw(document.getElementById("myList").value);
}
function draw(speed)
{
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
context.clearRect(0,0,canvas.width, canvas.height);
var centerX = canvas.width / 2;
var centerY = canvas.height / 2;
var radius = canvas.height / 2 - 20;
context.beginPath();
context.arc(centerX, centerY, radius, Math.PI*0.10, Math.PI*-1.1, true);
var gradience = context.createRadialGradient(centerX, centerY, radius-radius/2, centerX, centerY, radius-radius/8);
gradience.addColorStop(0, '#ff9000');
gradience.addColorStop(1, '#000000');
context.fillStyle = gradience;
context.fill();
context.closePath();
context.restore();
context.beginPath();
context.strokeStyle = '#ffff00';
context.translate(centerX,centerY);
var increment = 5;
context.font="15px Helvetica";
for (var i=-18; i<=18; i++)
{
angle = Math.PI/30*i;
sineAngle = Math.sin(angle);
cosAngle = -Math.cos(angle);
if (i % 5 == 0) {
context.lineWidth = 8;
iPointX = sineAngle *(radius -radius/4);
iPointY = cosAngle *(radius -radius/4);
oPointX = sineAngle *(radius -radius/7);
oPointY = cosAngle *(radius -radius/7);
wPointX = sineAngle *(radius -radius/2.5);
wPointY = cosAngle *(radius -radius/2.5);
context.fillText((i+18)*increment,wPointX-2,wPointY+4);
}
else
{
context.lineWidth = 2;
iPointX = sineAngle *(radius -radius/5.5);
iPointY = cosAngle *(radius -radius/5.5);
oPointX = sineAngle *(radius -radius/7);
oPointY = cosAngle *(radius -radius/7);
}
context.beginPath();
context.moveTo(iPointX,iPointY);
context.lineTo(oPointX,oPointY);
context.stroke();
context.closePath();
}
var numOfSegments = speed/increment;
numOfSegments = numOfSegments -18;
angle = Math.PI/30*numOfSegments;
sineAngle = Math.sin(angle);
cosAngle = -Math.cos(angle);
pointX = sineAngle *(3/4*radius);
pointY = cosAngle *(3/4*radius);
context.beginPath();
context.strokeStyle = '#000000';
context.arc(0, 0, 19, 0, 2*Math.PI, true);
context.fill();
context.closePath();
context.beginPath();
context.lineWidth=6;
context.moveTo(0,0);
context.lineTo(pointX,pointY);
context.stroke();
context.closePath();
context.restore();
context.translate(-centerX,-centerY);
}
</script>
</head>
<body onload="draw(120);">
<div>
Change the speed in the dropdown to see the dial position change
<select id="myList" onchange="redraw();">
<option value="120">Speed = 120</option>
<option value="30">Speed = 30</option>
<option value="50">Speed = 50</option>
<option value="60">Speed = 60</option>
<option value="140">Speed = 140</option>
<option value="160">Speed = 160</option>
</select>
</div>
<canvas class="canvas" id="myCanvas" width="600" height="600">
Your browser does not support the HTML5 canvas tag.</canvas>
</body>
</html>
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