How to create a polygon shape div

Question

I would like to create HTML element like on image here:

A problem is the DIV element has polygon shape instead of regular rectangle, will be placed above other elements as something like popup and inside that element there is necessary to show an image with rectangular shape in source but showed on web like filling all space included triangle on the left side.

Do you think is there any possibility to realize that without preparing showed images as transparent PNGs in proper polygon format? Only by CSS3 transform or use canvas or SVG?

Answer 1

One method could be to split the image into two containers which are 50% the size of the parent, transform each of them separately and position the backgrounds to look like they are one single image. The transform could either be a skew (used in the answer) or a perspective based rotation.

Note that since we are transforming the container, we have to apply the reverse effect to the actual image for it to look normal.

.image {
  position: relative;
  height: 150px;
  width: 450px;
  overflow: hidden;
}
.top-container,
.bottom-container {
  position: absolute;
  left: 0px;
  height: 50%;
  width: 100%;
  overflow: hidden;
  backface-visibility: hidden;
}
.top-container {
  top: 0px;
  transform-origin: right bottom;
  transform: skew(-20deg);
}
.bottom-container {
  bottom: 0px;
  transform-origin: right top;
  transform: skew(20deg);
  background-position: 0% 100%;
}
.top-container:after,
.bottom-container:after {
  position: absolute;
  content: '';
  height: 100%;
  width: 100%;
  left: -14px;  /* tan(20) * (height/2) / 2 */
  background: url(http://lorempixel.com/450/150);
  background-size: 100% 200%;
}
.top-container:after {
  top: 0px;
  transform: skew(20deg);
}
.bottom-container:after {
  bottom: 0px;
  transform: skew(-20deg);
  background-position: 0% 100%;
}

/* Just for demo */

body {
  background: linear-gradient(90deg, crimson, indianred, purple);
}
.image2 {
  margin-top: 10px;
  height: 150px;
  width: 450px;
  background: url(http://lorempixel.com/450/150);
}

<div class="image">
  <div class='top-container'></div>
  <div class='bottom-container'></div>
</div>


<!-- this is the actual image for comparison -->

<h3>Original Image</h3>
<div class='image2'></div>

---

I was about to suggest usage of SVG and clipPath but since Persijn has already posted that sample, I have added below a different version with polygon.

.vector {
  position: relative;
  height: 150px;
  width: 450px;
}
svg {
  position: absolute;
  top: 0px;
  left: 0px;
  height: 100%;
  width: 100%;
}
polygon {
  fill: url(#image);
}

/* Just for demo */

body {
  background: linear-gradient(90deg, crimson, indianred, purple);
}

<div class='vector'>
  <svg viewBox='0 0 450 150' preserveAspectRatio='none'>
    <defs>
      <pattern id='image' height='150' width='450' patternUnits='userSpaceOnUse'>
        <image xlink:href='http://lorempixel.com/450/150' height='150' width='450' />
      </pattern>
    </defs>
    <polygon points='15,0 450,0 450,150 15,150 0,75' />
  </svg>
</div>