Calculate height of div based off width & maintain

问题:

This question already has an answer here:

• Maintain the aspect ratio of a div with CSS 22 answers

I am looking for a pure CSS solution to what I have here done using jQuery to help.

Basically I have 3 divs that spread evenly in width in a container. They maintain a 3/4 ration with the height being calculated off of the width. Furthermore, each div has a background image that stays proportional and some text that is centered horizontally and vertically.

$(document).ready(function() {
  function setw() {
    var footdivwidth = $('footer div').width();
    var footdivheight = footdivwidth * .75;
    $('footer div').css({
      'height': footdivheight + 'px'
    });
    $('footer div span').html('w: ' + footdivwidth + '<br>h: ' + footdivheight);
  }
  setw();
  $(window).resize(function() {
    setw();
  })
});

FOOTER {
  max-width: 1000px;
  margin: 0 auto;
  background-color: rgba(0, 0, 0, 0.171);
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
}

FOOTER DIV {
  background-image: url('https://learnwebdesign.online/img/bg.jpg');
  background-position: center;
  background-size: cover;
  background-repeat: no-repeat;
  flex: 1;
  text-align: center;
  display: flex;
  align-items: center;
  justify-content: center;
}

FOOTER DIV SPAN {
  display: inline-block;
  text-align: center;
  background-color: rgba(165, 165, 165, 0.282);
  padding: 7px 15px;
  border-radius: 3px;
  color: #FFFFFF;
  text-transform: uppercase;
  font-weight: bold;
  letter-spacing: 2px;
  font-size: 21px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<footer>
  <div><span>left photo</span></div>
  <div><span>center photo</span></div>
  <div><span>right photo and more text</span></div>
</footer>

Here is a pen showing what I have. https://codepen.io/nom3d/pen/arGpBV

Here is a gif showing the effect when resized. Note the background image staying proportional and text staying centered.

Also wondering if it's not possible with just CSS, how to do this with plain javascript, would I need to add id's to my divs?

Update: here is a plain javaScript function to handle this task

function setHeight(el,val){
    var box = document.querySelectorAll(el);
    var i;
    for(i = 0;i < box.length;i++){
        var width = box[i].offsetWidth;
        var height = width * val;
        box[i].style.height = height + 'px';        
    }
}
// set your element to target and the ratio value
setHeight('footer div',.75);
window.onresize = function(event) {
    setHeight('footer div',.75);
};

回答1:

Maintaining specific height:width ratios in CSS is usually done by exploiting the fact that padding percentage is always calculated based on the element's width.

For example, let's say you had an element with width: 500px, height: 300px and padding: 10%. Now you might expect the top and bottom paddings to be 10% of height, and the left and right paddings to be 10% of width. However this would give unequal vertical and horizontal paddings which is counter-intuitive to what is intended - equal paddings of 10%. To make sense of this we need to base the padding percentage on the save dimension, and that dimension has been chosen to be the width.

Thus to have an element with height:width ratio of 3:4 at all times we can set the height to 0 and the bottom (or top) padding to 3/4 of the width.

In your example each item is given a width of 33% by Flex. For a ratio of 3:4 the bottom padding should be 33% * 3 / 4, or 24.74%. Your CSS might look like:

width: 33%;
height: 0;
padding-bottom: 24.75%;

Note that since the height is 0, the element will need to be relatively positioned with an absolutely positioned wrapper inside it. If you attempt to put content directly in the div, it will break the ratio. Your code above could be modified thus:

footer {
  max-width: 1000px;
  margin: 0 auto;
  background-color: rgba(0, 0, 0, 0.171);
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
}
footer div {
  background-image: url('https://learnwebdesign.online/img/bg.jpg');
  background-position: center;
  background-size: cover;
  background-repeat: no-repeat;
  position: relative;
  width: 33%;
  height: 0;
  padding-bottom: 24.75%;
}
footer div span {
  /* Used as content wrapper, with flex to centre content */
  position: absolute;
  top: 0; bottom: 0;
  left: 0; right: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  background-color: rgba(165, 165, 165, 0.282);
  padding: 7px 15px;
  border-radius: 3px;
  color: #FFFFFF;
  text-transform: uppercase;
  font-weight: bold;
  letter-spacing: 2px;
  font-size: 21px;
}

<footer>
  <div><span>left photo</span></div>
  <div><span>center photo</span></div>
  <div><span>right photo and more text</span></div>
</footer>

回答2:

You can simply consider the basic trick for maitaining the aspect ratio using padding.

Here is an example where I kept both examples so you can compare, the one using jQuery and the other using pure CSS.

$(document).ready(function() {
  function setw() {
    var footdivwidth = $('footer div').width();
    var footdivheight = footdivwidth * .75;
    $('footer.no-padd div').css({
      'height': footdivheight + 'px'
    });
    $('footer div span').html('w: ' + footdivwidth + '<br>h: ' + footdivheight);
  }
  setw();
  $(window).resize(function() {
    setw();
  })
});

FOOTER {
  max-width: 1000px;
  margin: 0 auto;
  background-color: rgba(0, 0, 0, 0.171);
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
}

FOOTER DIV {
  background-image: url('https://learnwebdesign.online/img/bg.jpg');
  background-position: center;
  background-size: cover;
  background-repeat: no-repeat;
  flex: 1;
  text-align: center;
  display: flex
}
FOOTER:not(.no-padd) DIV:before {
  content:"";
  padding-top: 75%;
}

FOOTER DIV SPAN {
  margin:auto;
  text-align: center;
  background-color: rgba(165, 165, 165, 0.282);
  padding: 7px 15px;
  border-radius: 3px;
  color: #FFFFFF;
  text-transform: uppercase;
  font-weight: bold;
  letter-spacing: 2px;
  font-size: 21px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<footer class="no-padd">
  <div><span>left photo</span></div>
  <div><span>center photo</span></div>
  <div><span>right photo and more text</span></div>
</footer>

<footer >
  <div><span>left photo</span></div>
  <div><span>center photo</span></div>
  <div><span>right photo and more text</span></div>
</footer>

回答3:

A quick pure CSS solution would involve to add to FOOTER DIV

  max-width: 333px;
  width: calc(100vw/3);
  height: calc(100vw*0.75/3);
  max-height: calc(333px*0.75);

and add to FOOTER

  width: 100vw;

// Javascript is only used in order to check the width/height ratio in console live.
$(document).ready(function() {

  $(window).resize(function() {
    console.log('width: ' + $('footer div').width() + ', height: ' + $('footer div').height());
  });
  
});

FOOTER {
  max-width: 1000px;
  width: 100vw;
  margin: 0 auto;
  background-color: rgba(0, 0, 0, 0.171);
  display: flex;
  flex-wrap: wrap;
  /*justify-content: space-between;*/
}

FOOTER DIV {
  background-image: url('https://learnwebdesign.online/img/bg.jpg');
  background-position: center;
  background-size: cover;
  background-repeat: no-repeat;
  flex: 1;
  text-align: center;
  display: flex;
  align-items: center;
  justify-content: center;
  max-width: 333px;
  width: calc(100vw/3);
  height: calc(100vw*0.75/3);
  max-height: calc(333px*0.75);
}

FOOTER DIV SPAN {
  display: inline-block;
  text-align: center;
  background-color: rgba(165, 165, 165, 0.282);
  padding: 7px 15px;
  border-radius: 3px;
  color: #FFFFFF;
  text-transform: uppercase;
  font-weight: bold;
  letter-spacing: 2px;
  font-size: 21px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<footer>
  <div><span>left photo</span></div>
  <div><span>center photo</span></div>
  <div><span>right photo and more text</span></div>
</footer>

回答4:

Have you tried with

footer div {
    height: 20vw;
}

there is also calc property for css which could be helpful

https://developer.mozilla.org/en-US/docs/Web/CSS/calc

回答5:

Probably a bit late, but will add my solution as well.

I thought I should keep it a general solution, so I decided to not use your Footer classes. But I'm sure you'll get the trick.

In my opinion the easiest way is to use the padding calculation to get a fixed ratio and some divs.

1. Flex container
2. Flex items (with the padding on it): This container is used to maintain the resolution. The amount of padding for it depends on the width of the item. For example: Item width = 100% --> Padding = (100/4)*3 --> 75% padding
3. Content container inside Flex-Item where you can put your stuff
4. Background-Div inside the content container
5. put everything you need as sibling to the background-div

Here's a fiddle to play around, some comments are in the code: https://jsfiddle.net/Hoargarth/Lry5gbsq/ Feel free to ask if you need anything

Just a quick note on all of those containers: You could do it with just the flex-item and one other container. But in my opinion, with the extra container it get's more flexible if you need any hover-events, animations or som other exotic stuff. For the simple solution see this fiddle: https://jsfiddle.net/Hoargarth/m57b9jcw/

.container {
  width: 100%;
  display: flex;
  flex-wrap: wrap;
}

/* padding bottom gives the height of the container, 33.33% padding would be a quadratic box. 100% would be the same height as the container's width. Therefore simple trignomometry, (100/4) * 3 = 75%; or for screen width > 500px: (33.33 / 4) * 3 for a 4/3 resolution. You'll find the media query at the end of the css. It's just to demonstrate that it's working with media queries as well. */
.item {
  position: relative;
  width: 100%;
  padding-bottom: 75%;
}

/* Overflow hidden so nothing can overlap to the other items */
.content-wrapper {
  position: absolute;
  overflow: hidden;
  width: 100%;
  height: 100%;
}

.image-holder {
  position: relative;
  height: 100%;
  background-image: url("https://previews.123rf.com/images/happydancing/happydancing1706/happydancing170600014/80282512-flat-lay-photo-of-workspace-desk-with-laptop-smartphone-blank-notebook-and-green-plant-with-copy-spa.jpg");
  background-size: cover;
  background-position: 50%;
  background-repeat: no-repeat;
}

/* Absolute positioned by 50% top, left; To completely center it, you have to translate the holder back by it's own half width and height transform: translate(-50%, -50%) */
.text-holder {
  position: absolute;
  top: 50%;
  left: 50%;
  padding: 10px;
  width: 70%;
  background-color: rgba(255, 255, 255, 0.5);
  transform: translate(-50%, -50%);
  text-align: center;
}

/* Simple media Query to test it. Be aware: If the item's width is changing, the padding has to change as well */
@media (min-width: 500px) {
  .item {
    width: 33.33%;
    padding-bottom: 24.75%;
  }
}

<div class="container">

  <div class="item">
    <div class="content-wrapper">
      <div class="image-holder"></div>
      <div class="text-holder">
        <p>
          Some Centered Text
        </p>
      </div>
    </div>
  </div>
  
  <div class="item">
    <div class="content-wrapper">
      <div class="image-holder"></div>
      <div class="text-holder">
        <p>
          Some Centered Text but larger and longer so we see a difference
        </p>
      </div>
    </div>
  </div>
  
  <div class="item">
    <div class="content-wrapper">
      <div class="image-holder"></div>
      <div class="text-holder">
        <p>
          Groot
        </p>
      </div>
    </div>
  </div>
  
</div>

回答6:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        FOOTER {
            max-width: 1000px;
            margin: 0 auto;
            background-color: rgba(0, 0, 0, 0.171);
            display: flex;
            flex-wrap: wrap;
            justify-content: space-between;
        }
        FOOTER DIV {
            position: relative;
            width: calc(100vw / 3);
            height: calc(100vw / 3 * 0.75 );
            max-height: calc(1000px / 3 * 0.75 );
            background-image: url('https://learnwebdesign.online/img/bg.jpg');
            background-position: center;
            background-size: cover;
            background-repeat: no-repeat;
            flex: 1;
            text-align: center;
            display: flex;
            align-items: center;
            justify-content: center;

        }
        FOOTER DIV SPAN {
            position: absolute;
            top:50%;
            left: 50%;
            transform: translate(-50%, -50%);
            display: inline-block;
            text-align: center;
            background-color: rgba(165, 165, 165, 0.282);
            padding: 7px 15px;
            border-radius: 3px;
            color: #FFFFFF;
            text-transform: uppercase;
            font-weight: bold;
            letter-spacing: 2px;
            font-size: 21px;
        }
    </style>
</head>
<body>
    <footer>
        <div><span>left photo</span></div>
        <div><span>center photo</span></div>
        <div><span>right photo and more text</span></div>
    </footer>
</body>
</html>

You can Directly use given code, For making propostional width height, You have 2 different ways, one of them given below, you can use width in percentage and height with calc with the same,

another way give width in %, and instead of height you can give padding-bottom in percentage, the all are in same propostion.

回答7:

Here's a more generic way to go about this for anyone who doesn't want to dig through the OP's code and just needs a solution to responsive fixed ratio elements with CSS.

The basic idea is that padding as a percentage is calculated based on the element's width. This means that padding-bottom: 100% == element.width (In this case a square). We can hijack that trick by calculating the ratio and using that for padding.

---

Image Example

Images are a bit odd in that they already have an aspect ratio so you could simply set the height: auto and be good to go.

Ratio: 4:3

img {
  --aspectRatio: calc(3/4 * 100%);
  display:block;
  width: 300px; // this one needs a width to work.
  height:var(--aspectRatio);
}

<img src="https://images.unsplash.com/photo-1559666126-84f389727b9a" />

---

Image Background

But let's say you want the container to manage the size regardless of the original content ratio? Simply use a background image.

This one is 16:9 (typical widescreen)

.fixedAspect {
  --aspectRatio: calc(9/16 * 100%);
  height: 0;
  padding-bottom: var(--aspectRatio);
  background-size: cover;
  background-position: center center;
}

<div class="fixedAspect" style="background-image: url(https://images.unsplash.com/photo-1559662780-c3bab6f7e00b)"></div>

HTML Element with content

Adding content to an element with a height:0 and a bunch of padding is probably not the best solution. But we can solve this by using a pseudo-class. To force a "minimum height".

Bonus: This won't break if your content is bigger than the aspect ratio you've defined the way a position: absolute; wrapper would.

.fixedAspect {
  margin: 20px;
  background-color: #f6f3f0;
}

p {
  font-family: Helvetica, Arial, Sans-Serif;
  padding: 10px;
}

.fixedAspect:before {
  --aspectRatio: calc(5/20 * 100%);
  content: "";
  height:0;
  padding-top: var(--aspectRatio);
  
  /* so you can see the element */
  background-color: #F47E20;
  
  /* get this out of the way */
  float: left;
  width: 1px;
  margin-left:-1px;
}

.fixedAspect:after {
  /* we need to clear the float so its container respects height */
  content: "";
  display: table;
  clear: both;
}

<div class="fixedAspect">
  <p>My default size is a ratio of 20:5 but I'll grow if there's too much content.</p>
</div>

回答8:

PURE CSS FIX

Adjust width and height accordingly

footer {
    display: flex;
    width: 100vw;
    align-items: center;
    justify-content: center;
}

.responsive-box {
    width: 33vw;
    border: 1px solid blue;
    max-width: 333px;
    min-width: 35px;
    flex-flow: row;
    height: 60vh;
  position: relative;
}

.responsive-box span {
   position: absolute;
   top:40%;
   bottom:0;
   left:0;
   right:0;
   text-align: center;
}

<footer>
  <div class="responsive-box left"><span>left photo</span></div>
  <div class="responsive-box center"><span>center photo</span></div>
  <div class="responsive-box right"><span>right photo and more text</span></div>
</footer>