Canvas HTML animation that includes a shake effect

Question

I have an animation created using canvas. The animation is almost complete, and it shows an explosion. I was wondering if there is a way to create a trembling effect that would seem as if the contents of the canvas were trembling for several seconds when an explosion occurs.

Any help was appreciated.

Answer 1

An easy way to stagger the screen is to translate the entire context in a random direction before each draw.
You must save / restore the context in order to keep it in a “clean” state.

var ctx=cv.getContext('2d');

function preShake() {
  ctx.save();
  var dx = Math.random()*10;
  var dy = Math.random()*10;
  ctx.translate(dx, dy);  
}

function postShake() {
  ctx.restore();
}

function drawThings() {  
  ctx.fillStyle = '#F00';
  ctx.fillRect(10, 10, 50, 30);
  ctx.fillStyle = '#0F0';
  ctx.fillRect(140, 30, 90, 110);
  ctx.fillStyle = '#00F';
  ctx.fillRect(80, 70, 60, 40);
}

drawThings();

function animate() {
  // keep animation alive
  requestAnimationFrame(animate);
  // erase
  ctx.clearRect(0,0,cv.width, cv.height);
  //
  preShake();
  //
  drawThings();
  //
  postShake();
}

animate();

  <canvas id='cv'></canvas>

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, sin , :

var ctx=cv.getContext('2d');

var shakeDuration = 800;
var shakeStartTime = -1;

function preShake() {
  if (shakeStartTime ==-1) return;
  var dt = Date.now()-shakeStartTime;
  if (dt>shakeDuration) {
      shakeStartTime = -1; 
      return;
  }
  var easingCoef = dt / shakeDuration;
  var easing = Math.pow(easingCoef-1,3) +1;
  ctx.save();  
  var dx = easing*(Math.cos(dt*0.1 ) + Math.cos( dt *0.3115))*15;
  var dy = easing*(Math.sin(dt*0.05) + Math.sin(dt*0.057113))*15;
  ctx.translate(dx, dy);  
}

function postShake() {
  if (shakeStartTime ==-1) return;
  ctx.restore();
}

function startShake() {
   shakeStartTime=Date.now();
}

function drawThings() {  
  ctx.fillStyle = '#F00';
  ctx.fillRect(10, 10, 50, 30);
  ctx.fillStyle = '#0F0';
  ctx.fillRect(140, 30, 90, 110);
  ctx.fillStyle = '#00F';
  ctx.fillRect(80, 70, 60, 40);
}

drawThings();

function animate() {
  // keep animation alive
  requestAnimationFrame(animate);
  // erase
  ctx.clearRect(0,0,cv.width, cv.height);
  //
  preShake();
  //
  drawThings();
  //
  postShake();
}

startShake();
setInterval(startShake,2500);
animate();

  <canvas id='cv'></canvas>

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