Yan Cui
I help clients go faster for less using serverless technologies.
Whilst working on the MathDOJO mini game one of the neat little things I tried to do was implement a time meter which steadily counts down and changes colour (from green to yellow to glowing red) as it approaches 0:
First, you need something to represent the meter, a simple <span> element will do:
1: <body>
2: <span id="count-down-meter"></span>
3: </body>
Then you need CSS to define its colour (and glow effect using CSS3 animation which for now, is only supported by webkit browser unfortunately) at different stages
1: /* define the animation (webkit-only) */
2: @-webkit-keyframes redPulse
3: {
4: from { -webkit-box-shadow: 0 0 9px #f00; }
5: 50% { -webkit-box-shadow: 0 0 18px #f00; }
6: to { -webkit-box-shadow: 0 0 9px #f00; }
7: }
8:
9: /* initial state of the meter */
10: #count-down-meter
11: {
12: display: block;
13: width: 100%;
14: height: 15px;
15: margin-top: 10px;
16: background-color: #0f0;
17: }
18:
19: /* change color at midway */
20: #count-down-meter.middle
21: {
22: background-color: #ff0;
23: }
24:
25: /* change colour and play animation when it's on its last leg */
26: #count-down-meter.lastleg
27: {
28: background-color: #f00;
29: -webkit-animation-name: redPulse;
30: -webkit-animation-duration: 2s;
31: -webkit-animation-iteration-count: infinite;
32: }
The animation itself is handled by Javascript, using JQuery’s animate method:
1: function start() {
2: // change to yellow when 40% way through
3: var midWidth = meter.width() * 0.6,
4: // change to glowing red when 70% way through
5: lastlegWidth = meter.width() * 0.3;
6:
7: meter.animate({
8: width: 0 + "px",
9: }, {
10: duration: 5000,
11: easing: "linear",
12: step: function(now, fx) {
13: if (now <= midWidth) {
14: meter.addClass("middle");
15:
16: if (now <= lastlegWidth) {
17: meter.addClass("lastleg");
18: }
19: }
20: }
21: });
22: };
To reset the state changes to the meter afterwards, it’s easiest to remove the “style” attribute as JQuery applies the changes through the “style” attribute, which can be a problem if you had manually inserted style in your HTML:
1: function reset() {
2: meter.stop()
3: .removeAttr("style")
4: .removeClass("middle")
5: .removeClass("lastleg");
6: };
Here’s a live demo:
So that’s it, nice and easy! Enjoy! Hope you find some good use for it.
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