HTML & CSS - - By Guy Routledge

AtoZ CSS Screencast: The rotateY CSS Transform

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This screencast is a part of our AtoZ CSS Series. You can find other entries to the series here.

Transcript

In the previous episode we learned about the transform property and the value translateX().

In this episode we’ll be digging deeper into transforms and manipulating elements in 3D.

In this episode we’ll learn all about:

  • 3D space in CSS
  • How to rotate elements around their vertical and horizontal axis
  • And how perspective works

3D space

The browser acts a bit like a two-dimensional canvas on which we layout blocks of content and style images, text and links to create a website or web app.

If you recall high-school maths, when looking at a graph there is a horizontal x-axis and a vertical y-axis.

There’s a third axis that comes directly out from the screen, known as the z-axis. We’ll look into this more in the final episode of this season when we talk about z-index. For now, we just need to know that there is a third dimension and we can transform elements from being in a 2D plane to a 3D one using 3D transforms.

When dealing with elements in 3D space, we can ensure they appear visually as if they are in a third plane by setting the transform-style property to preserve-3d on the parent container.

This will allow all child elements to appear in 3D space. If this property is not set, elements will appear flattened and the effect won’t be as obvious.

Rotate

Rotation can be very useful in many aspects of design – from a complete 180 to just a small handful of degrees.

The default axis of rotation is the z-axis.

The amount of rotation can be specified in degrees or radians. I vaguely remember radians from maths class but I always use degrees because they feel a lot more comfortable to me.

I’ve got an image here with a white border around it and a drop shadow. If I wanted to rotate the image, I can do so by using the transform property and the the rotate() function.

A positive value with rotate clockwise and a negative value, anti-clockwise.

img {
  transform: rotate(10deg);
}

This is the same as using the single-axis rotation of rotateZ() as the image is rotating around the z-axis.

When using rotateY(), the image rotates around the y-axis which can be a useful trick to achieve something like a card flip effect or something similar.

img {
  transform: rotateY(45deg);
}

If I add in an animation that continuously rotates the image around the y-axis, it should be a bit clearer as to what’s going on.

img {
  animation: spin 2s infinite linear;
}
@keyframes spin {
  from {transform: rotateY(0deg);}
  to {transform: rotateY(360deg);}
}

You may notice that when the element rotates around 180 degrees, the image appears to become a mirror image. By default, the back of the image is visible even when rotated around so the front face of it is pointing away from the viewer.

The visibility of the back of the element can be controlled with the backface-visibility property. It takes the values visible or hidden where visible is the default.

A slightly more sane use of rotate is to add subtle effects to elements on the page. The browser support is IE9+ but because this is a fairly unimportant cosmetic bit of styling, having non-rotated elements in old IE isn’t a big deal to me. It’s always worth testing to be on the safe side, though – just in case.

Perspective

When dealing with elements in 3D space, we can make the visual effect more extreme by bringing perspective into the equation.

Back in art class you might have learned that to achieve the effect of three dimensions on a 2D piece of paper, you can draw a series of straight lines from a vanishing point and ensure all horizontal features moving away from the viewer all converge at that point.

This photo illustrates perspective quite nicely. But how does this feature in CSS?

Here I’ve got the markup for a cube. The six faces of the cube are contained within the “cube-x” <div> which is contained within two others so eventually we can take a look at rotating the cube in three dimensions.

<div class="container"> 
  <div class="cube-z"> 
    <div class="cube-y"> 
      <div class="cube-x"> 
        <div class="face-one">1</div> 
        <div class="face-two">2</div> 
        <div class="face-three">3</div> 
        <div class="face-four">4</div> 
        <div class="face-five">5</div> 
        <div class="face-six">6</div> 
      </div> 
    </div> 
  </div> 
</div>
.container {
  width: 400px;
  margin: 100px auto;
}
[class^="cube"] {
  position: relative;
  width: 200px;
  height: 200px;
  transform-style: preserve-3d;
}
[class^="face-"] {
  position: absolute;
  width: 200px;
  height: 200px;
  padding: 20px;
  color: rgba(0,0,0,0.75);
  border: 1px solid;

  font-size: 160px;
  font-family: Avenir;
  line-height: 1;
  text-align: center;
}

.face-one {
  transform: translateZ(100px);
  background-color: hsla(329,58%,52%,0.8);  
}
.face-two {
  transform: rotateX(90deg) translateZ(100px);
  background-color: hsla(0,0%,13%,0.8);
}
.face-three {
  transform: rotateY(90deg) translateZ(100px);
  background-color: hsla(54,70%,68%,0.8);
}
.face-four {
  transform: rotateY(-90deg) translateZ(100px);
  background-color: hsla(190,81%,67%,0.8);
}
.face-five {
  transform: rotateX(-90deg) translateZ(100px) rotate(180deg);
  background-color: hsla(261,100%,75%,1.0);
}
.face-six {
  transform: rotateY(180deg) translateZ(100px);
  background-color: hsla(84,76%,53%,0.8);
}
.cube-z {transform: rotateZ(0deg);}
.cube-y {transform: rotateY(0deg);}
.cube-x {transform: rotateX(0deg);}

At the moment the first face of the cube is visible on a 2D plane and none of the other sides are visible.

If I rotate the “container” around the y-axis, we’ll be able to see each side in turn.

.cube-z {animation: spin 4s infinite linear;}

@keyframes spin {
  from {transform: rotateY(0deg);}
  to {transform: rotateY(360deg);}
}

This gives us a sense of three dimensions but if we add a bit of perspective, the effect becomes much clearer and a real sense of 3D is achieved.

.container {
  perspective: 500px;
  perspective-origin: 25% 50%;
}

I’ll stop the animation and let’s have a look at what’s going on here.

The perspective property controls the distance between the viewer and the zero point of the z-axis. A higher value moves the viewer further away, a lower value, moves the viewer closer which drastically increases the impact of the 3D positioning.

We can control the placement of the vanishing point by changing the perspective-origin property.

This property takes two length values, the first for the horizontal position and the second for the vertical. Manipulating these values changes the angle of view of the element and when the animation is turned back on, the effect can be quite striking.

We’re almost at an end to this AtoZ series, so watch this space for the final letter where I discuss using the z-index.

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