javascript - CSS Transform Math - Calculate height of div caused by skew

I'm having difficulty figuring out how I could calculate the extra height of a div container caused by skewing it. I am masking an image inside the container and resizing it using a plugin.

The containers will not always have the same height and width so using fixed dimensions will not work.

Please see my demo. /

HTML

<div id="profiles" class="container">
        <div class="profile">
            <div class="image">
                <img src="" alt="">
            </div>
            <div class="detail">
            </div>
        </div>
        <div class="profile">
            <div class="image">
                <img src="" alt="">
            </div>          
            <div class="detail">
            </div>
        </div>        
        <div class="profile">
            <div class="image">
                <img src="" alt="">
            </div>          
            <div class="detail">
            </div>
        </div>
        <div class="profile">
            <div class="image">
                <img src="" alt="">
            </div>          
            <div class="detail">
            </div>
        </div>        
        <div class="profile">
            <div class="image">
                <img src="" alt="">
            </div>          
            <div class="detail">
            </div>
        </div>
        <div class="profile">
            <div class="image">
                <img src="" alt="">
            </div>          
            <div class="detail">
            </div>
        </div>            
</div>

CSS

#profiles {
    margin-top: 300px;
    transform:skewY(-30deg);
    -ms-transform:skewY(-30deg); /* IE 9 */
    -webkit-transform:skewY(-30deg); /* Safari and Chrome */    
}
.profile {
    cursor: pointer;
    float: left;
    width: 32.25%;
    margin: 0.5%;
    position: relative;
}
.profile .image {
    position: relative;
    overflow: hidden;
    height: 400px;
    background: #000;
    backface-visibility:hidden;
    -webkit-backface-visibility:hidden; /* Chrome and Safari */
    -moz-backface-visibility:hidden; /* Firefox */
    -ms-backface-visibility:hidden; /* Internet Explorer */     
}
.profile .image * {
    position: relative;
    transform:skew(0deg,30deg);
    -ms-transform:skew(0deg,30deg); /* IE 9 */
    -webkit-transform:skew(0deg,30deg); /* Safari and Chrome */         
}

I'm having difficulty figuring out how I could calculate the extra height of a div container caused by skewing it. I am masking an image inside the container and resizing it using a plugin.

The containers will not always have the same height and width so using fixed dimensions will not work.

Please see my demo. http://jsfiddle.net/RyU9W/6/

HTML

<div id="profiles" class="container">
        <div class="profile">
            <div class="image">
                <img src="http://placekitten.com/g/750/750" alt="">
            </div>
            <div class="detail">
            </div>
        </div>
        <div class="profile">
            <div class="image">
                <img src="http://placekitten.com/g/750/750" alt="">
            </div>          
            <div class="detail">
            </div>
        </div>        
        <div class="profile">
            <div class="image">
                <img src="http://placekitten.com/g/750/750" alt="">
            </div>          
            <div class="detail">
            </div>
        </div>
        <div class="profile">
            <div class="image">
                <img src="http://placekitten.com/g/750/750" alt="">
            </div>          
            <div class="detail">
            </div>
        </div>        
        <div class="profile">
            <div class="image">
                <img src="http://placekitten.com/g/750/750" alt="">
            </div>          
            <div class="detail">
            </div>
        </div>
        <div class="profile">
            <div class="image">
                <img src="http://placekitten.com/g/750/1200" alt="">
            </div>          
            <div class="detail">
            </div>
        </div>            
</div>

CSS

#profiles {
    margin-top: 300px;
    transform:skewY(-30deg);
    -ms-transform:skewY(-30deg); /* IE 9 */
    -webkit-transform:skewY(-30deg); /* Safari and Chrome */    
}
.profile {
    cursor: pointer;
    float: left;
    width: 32.25%;
    margin: 0.5%;
    position: relative;
}
.profile .image {
    position: relative;
    overflow: hidden;
    height: 400px;
    background: #000;
    backface-visibility:hidden;
    -webkit-backface-visibility:hidden; /* Chrome and Safari */
    -moz-backface-visibility:hidden; /* Firefox */
    -ms-backface-visibility:hidden; /* Internet Explorer */     
}
.profile .image * {
    position: relative;
    transform:skew(0deg,30deg);
    -ms-transform:skew(0deg,30deg); /* IE 9 */
    -webkit-transform:skew(0deg,30deg); /* Safari and Chrome */         
}

Share Improve this question edited Jul 31, 2019 at 14:09 asked Sep 6, 2013 at 17:34 hyperdrive 1,8465 gold badges21 silver badges36 bronze badges

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5 Answers 5

Sorted by: Reset to default 8 In skew we have a case of Right-angled triangle and the skew new width is equal to "Opposite" and we've the angle and the opposite so by this equation we can get the adjacent Opposite = Adjacent * tan(angle); Where opposite in case of skewX is the div height and in case of skewY will be the div width

Check this https://codepen.io/minaalfy/pen/exgvjb

function calculateSkew(){
  var el = document.getElementById('bluebox');
  var skewX = document.getElementById('skewX');
    skewX.value = skewX.value || 0;
  var skewY = document.getElementById('skewY');
    skewY.value = skewY.value || 0;
    
  var yRadians = skewY.value * Math.PI / 180;
  var newHeight = el.offsetWidth * Math.tan(yRadians);
  var calculatedHeight = el.offsetHeight + newHeight;
  
  var xRadians = skewX.value * Math.PI / 180;
  var newWidth = calculatedHeight * Math.tan(xRadians);
  var calculatedWidth = el.offsetWidth + newWidth;
  
  el.style.transform = ("skewX(" + skewX.value + "deg ) skewY(" + skewY.value  + "deg )");
  var output = document.getElementById('output');
  output.innerHTML = "skewY by "+skewY.value+ " and new height calculated is "+calculatedHeight+ "<br> skewX by "+skewX.value+ " and the new calculated width is "+ calculatedWidth;
}

body {text-align:center}
#bluebox {width:100px;height:100px;background:blue;margin: 20px auto;}

<h4>Enter any numeric value for skewX or skewY to calculate the new width&height for the box</h4>
<div id="bluebox"></div>
<input type="number" placeholder="skewX" id="skewX" onkeyup="calculateSkew()" />
<input type="number" placeholder="skewY" id="skewY" onkeyup="calculateSkew()" />
<h1 id="output"></h1>

I got it using this solution.

var degrees = 30;
var radians= degrees*Math.PI/180;
var newHeight = parentWidth*Math.tan(radians);
var newOffset = newHeight / 2;
var parentHeight = parentHeight + newHeight;

Here is my updated fiddle with option to select degrees

http://jsfiddle.net/bhPcn/5/

Two functions that could help you.

function matrixToArray(matrix) {
    return matrix.substr(7, matrix.length - 8).split(', ');
}

function getAdjustedHeight(skewedObj){
    var jqElement = $(skewedObj);
    var origWidth= jqElement.width();
    var origHeight= jqElement.height();
    var matrix = matrixToArray(jqElement.css('transform'))
    var alpha = matrix[2];
    var adjusted = Math.sin(alpha)*origWidth/Math.sin(Math.PI/2-alpha);
    return origHeight+Math.abs(adjusted);
}

function getAdjustedWidth(skewedObj){
    var jqElement = $(skewedObj);
    var origWidth= jqElement.width();
    var origHeight= jqElement.height();
    var matrix = matrixToArray(jqElement.css('transform'))
    var alpha = matrix[1];
    var adjusted = Math.sin(alpha)*origHeight/Math.sin(Math.PI/2-alpha);
    return origWidth+Math.abs(adjusted);
}

Usage (http://jsfiddle.net/x5her/18/):

 // if you use scewY
 console.log(getAdjustedWidth($(".image")[0]))


 // if you use scewX
 console.log(getAdjustedHeight($(".image")[0]))

Example of dynamic skew angle depending on the height.

In angular:

  // We use a mathematical expression to define the degree required in skew method
  // The angle depend on the height and width of the container

  // We turn the answer from atan which is in radian into degrees
  //
  // DEGREES = RADIAN * 180 / PI
  const degrees = Math.atan(
                    parent.nativeElement.clientWidth / parent.nativeElement.clientHeight
                  ) * 180 / Math.PI;

  parent.nativeElement.children[0].style.transform = `skew(${degrees}deg)`;
  parent.nativeElement.children[1].style.transform = `skew(${degrees}deg)`;

In Jquery for the snippet :

$(document).ready(() => {
  const parent = $('.duo:first');

  const degrees = Math.atan(parent.width() / parent.height()) * 180 / Math.PI;

  $('.first').css('transform', `skew(${degrees}deg)`);
  $('.second').css('transform', `skew(${degrees}deg)`);
});

.container {
  width: 10em;
  height: 10em;
  display: flex;
  flex-direction: row;
  flex-wrap: nowrap;
}

.one-square {
  height: 100%;
  width: 0;
  flex-grow: 1;
  display: flex;
}

.duo {
  height: 100%;
  width: 0;
  flex-grow: 1;
  display: flex;
  flex-direction: row;
  position: relative;
  overflow: hidden;
}

.first {
  width: 100%;
  height: 100%;
  background-color: red;
  transform: skew(0deg);
  transform-origin: 0 0;
  position: absolute;
}

.second {
  width: 100%;
  height: 100%;
  background-color: yellow;
  transform: skew(0deg);
  transform-origin: 100% 100%;
  position: absolute;
}

.a {
  background-color: grey;
}

.b {
  background-color: green;
}

.c {
  background-color: lightgrey;
}

.d {
  background-color: #444444;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="container">
  <div class="one-square a"></div>
  <div class="one-square b"></div>

  <div class="duo">
    <div class="first">
    </div>

    <div class="second">
    </div>
  </div>

  <div class="one-square c"></div>
  <div class="one-square d"></div>
</div>

Now that it's 2021, just use el.getBoundingClientRect().height. It takes css transform into its calculations.

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javascript - CSS Transform Math - Calculate height of div caused by skew - Stack Overflow

5 Answers 5

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