Radar scanner rotation effect

Question

I'm trying to figure out a possible solution on how to create a radar scanner effect using jQuery and CSS. Essentially, a semi-transparent triangle beam would rotate around the middle point of a div. Is this possible with jQuery or should I resort to some other means?
I prefer to not use animated gifs.

Answer 1

You don't need jQuery in order to achieve a radar scanner

• For the infinite radar beam rotation use just CSS animation and CSS rotate one full turn 1turn as linear and infinite timing.
• Inside JavaScript, handle the dots opacity with requestAnimationFrame to continually get the current beam rotation angle, convert the dots x, y to angle, and calculate the opacity delta given the normalized differences in the two angles

const getCSSVal = (e, v) => e.style.getPropertyValue(v);
const mod = (n, m) => ((n % m) + m) % m; // Fix negative Modulo
const PI = Math.PI;
const TAU = PI * 2;

const radar = (elRadar) => {

  const elBeam = elRadar.querySelector(".beam");
  const elsDot = elRadar.querySelectorAll(".dot");

  const update = () => {
    const beamAngle = parseFloat(getComputedStyle(elBeam).getPropertyValue("rotate")) * PI / 180 || 0;

    elsDot.forEach(elDot => {
      const x = getCSSVal(elDot, "--x") - 0.5;
      const y = getCSSVal(elDot, "--y") - 0.5;
      const dotAngle = mod(Math.atan2(y, x), TAU);
      const opacity = mod(dotAngle - beamAngle, TAU) / TAU;
      elDot.style.opacity = opacity;
    });

    requestAnimationFrame(update);
  };
  
  update();
};

document.querySelectorAll(".radar").forEach(radar);

.radar {
  position: relative;
  overflow: hidden;
  width: 300px;
  aspect-ratio: 1;
  background: #000 url(https://i.stack.imgur.com/vY6Tl.png) center / cover;
  border-radius: 50%;
}

.beam {
  position: absolute;
  top: 0;
  left: 0;
  width: inherit;
  aspect-ratio: inherit;
  background: url(https://i.stack.imgur.com/GCbf1.png) center / cover;
  animation: 5s rotate linear infinite;
}

@keyframes rotate {
  100% {
    rotate: 1turn;
  }
}

.dot {
  position: absolute;
  left: calc(var(--x) * 100%);
  top: calc(var(--y) * 100%);
  border-radius: 50%;
  width: 4px;
  height: 4px;
  margin: -2px;
  background: #cf5;
  box-shadow: 0 0 10px 5px rgba(100, 255, 0, 0.5);
  opacity: 0;
}

<div class="radar">
  <div class="beam"></div>
  <div class="dot" style="--x:0.7; --y:0.2"></div>
  <div class="dot" style="--x:0.2; --y:0.3"></div>
  <div class="dot" style="--x:0.6; --y:0.1"></div>
  <div class="dot" style="--x:0.4; --y:0.6"></div>
  <div class="dot" style="--x:0.9; --y:0.7"></div>
</div>

Answer 2

CSS only demonstration

HTML:

<div id="radar">
    <div class="beacon" id="beacon"></div>
    <div class="beacon" id="beacon-75"></div>
    <div class="beacon" id="beacon-50"></div>
    <div class="beacon" id="beacon-25"></div>
    <div class="circle" id="circle-big"></div>
    <div class="circle" id="circle-medium"></div>
    <div class="circle" id="circle-small"></div>
    <div class="circle" id="dot"></div>
    <div id="vertical"></div>
    <div id="horizontal"></div>
</div>

CSS:

#radar {
    position:relative;
    width:400px;
    height:400px;
    margin:20px auto;
    border:3px solid #0c0;
    background-color:#020;
    border-radius:50%;
}
#radar>* {position:absolute}
.beacon {
    left:50%;
    top:50%;
    border-style:solid;
    border-width:8px 200px 8px 0;
    border-color:transparent;
    margin-top:-8px;
    transform-origin:0 50%;
}
#beacon {border-right-color:#0c0;animation:spin 2s 0s linear infinite}
#beacon-75 {border-right-color:rgba(0,204,0,0.75);animation:spin 2s 0.03s linear infinite}
#beacon-50 {border-right-color:rgba(0,204,0,0.5);animation:spin 2s 0.06s linear infinite}
#beacon-25 {border-right-color:rgba(0,204,0,0.25);animation:spin 2s 0.09s linear infinite}
.circle {
    left:50%;
    top:50%;
    border:1px solid #0c0;
    border-radius:50%;
}
#circle-big {
    width:300px;
    height:300px;
    margin:-150px;
}
#circle-medium {
    width:200px;
    height:200px;
    margin:-100px;
}
#circle-small {
    width:100px;
    height:100px;
    margin:-50px;
}
#dot {
    width:8px;
    height:8px;
    margin:-4px;
    background-color:#0c0;
}
#vertical {
    left:50%;
    top:0;
    bottom:0;
    border-left:1px solid #0c0;
}
#horizontal {
    top:50%;
    left:0;
    right:0;
    border-top:1px solid #0c0;
}

@keyframes spin {
    from {transform:rotate(0)}
    to {transform:rotate(360deg)}
}

Please note that to support some browsers you will need to add vendor prefixes, but this by itself works in IE10 and Firefox.