Design Atlas
한국어
◧ Film & photo

The 180-degree rule

180도 법칙

Keep the camera on one side of the imaginary axis between two subjects across every cut, so their left/right positions never flip and confuse the viewer.

Also known as: 라인 규칙Line of actionCrossing the line
···
html
<div class="stage">
  <div class="top">
    <div class="axis"></div>
    <div class="char ca">A</div>
    <div class="char cb">B</div>
    <div class="cam" id="cam"></div>
    <span class="warn" id="warn">LINE CROSSED</span>
  </div>
  <div class="frames">
    <div class="frame"><i class="p left" id="f1l">A</i><i class="p right" id="f1r">B</i></div>
    <div class="frame" id="f2"><i class="p left" id="f2l">A</i><i class="p right" id="f2r">B</i></div>
  </div>
</div>
css
.stage{position:absolute;inset:0;display:flex;gap:4%;padding:4%;box-sizing:border-box}
.top{position:relative;flex:1.3;background:color-mix(in oklab,var(--accent) 6%,var(--surface));
  border-radius:8px;border:1px solid var(--line)}
.axis{position:absolute;left:20%;right:20%;top:50%;height:1px;
  background:repeating-linear-gradient(90deg,var(--muted) 0 6px,transparent 6px 11px)}
.char{position:absolute;top:50%;width:13%;aspect-ratio:1;border-radius:50%;transform:translate(-50%,-50%);
  display:grid;place-items:center;font:800 11px system-ui,sans-serif;color:#fff}
.ca{left:20%;background:var(--accent)}
.cb{left:80%;background:var(--accent-2)}
.cam{position:absolute;width:6%;aspect-ratio:1;border-radius:2px;background:var(--fg);transform:translate(-50%,-50%)}
.warn{position:absolute;left:50%;top:3%;transform:translateX(-50%);font:800 10px ui-monospace,monospace;
  color:#ff4d5e;opacity:0;transition:opacity .3s;letter-spacing:.05em}
.warn.show{opacity:1}
.frames{flex:1;display:flex;flex-direction:column;gap:6%}
.frame{position:relative;flex:1;border-radius:6px;border:2px solid var(--line);background:var(--surface);
  transition:border-color .3s}
.frame.bad{border-color:#ff4d5e}
#f1l{left:12%}
#f1r{left:64%}
.p{position:absolute;top:50%;width:20%;aspect-ratio:1;border-radius:50%;transform:translateY(-50%);
  transition:left .5s ease;display:grid;place-items:center;color:#fff;font:800 10px system-ui,sans-serif}
.p.left{background:var(--accent)}
.p.right{background:var(--accent-2)}
js
const cam=document.getElementById('cam');
const f2=document.getElementById('f2');
const f2l=document.getElementById('f2l'), f2r=document.getElementById('f2r');
const warn=document.getElementById('warn');
function frame(t){
  const cycle=6000;
  const phase=(t%cycle)/cycle;
  const crossed=phase>0.72 && phase<0.92;
  const side=crossed?-1:1;
  const ang=phase*Math.PI*2*2.4;
  const localAngle=Math.PI*0.22+(Math.sin(ang)*0.5+0.5)*Math.PI*0.56;
  const x=50+Math.cos(localAngle)*17;
  const y=50+side*Math.sin(localAngle)*15;
  cam.style.left=x+'%';
  cam.style.top=y+'%';
  const orderNormal=side>0;
  f2l.style.left=orderNormal?'12%':'64%';
  f2r.style.left=orderNormal?'64%':'12%';
  f2.classList.toggle('bad',!orderNormal);
  warn.classList.toggle('show',!orderNormal);
  requestAnimationFrame(frame);
}
requestAnimationFrame(frame);

When two people talk, the imaginary line connecting them is called the line of action. Keep the camera on one side of it, and no matter how you cut between shots, subject A stays on the left of frame and B stays on the right.

Cross that line mid-scene, and the next cut suddenly flips A and B's positions. Cut the two shots together and the spatial sense breaks — it reads like the characters teleported, and the audience loses track of where everyone is.

When a scene genuinely needs to cross the line — a multi-camera shoot, a scene transition — directors bridge it with a neutral shot taken right on the axis, or a camera move that physically tracks across it, so the reset feels motivated instead of jarring.

When to use

Follow it any time a conversation or interview is cut across multiple shots. Crossing it on purpose to disorient the audience is a real technique, but a rare one.