Animating with Clip-Path

Clip-Path animation: Play with CSS shape deformation animation

clip-path is a powerful tool in CSS properties, but is often overlooked. It needs to deal with geometry and different values, so it looks a bit like a math class. This article will explore in-depth clip-path , especially how to use it to create complex animation effects that show the power of its shape transformation.

clip-path crash course

MDN's description of clip-path is as follows:

clip-path CSS property creates a clip area that sets which part of the element should be displayed. The parts inside the area are displayed, and the parts outside the area are hidden.

Taking the circle provided by clip-path as an example, after defining the circle, the inner area of ​​the circle is "positive space" and the outer area of ​​the circle is "negative space". Positive space is rendered, negative space is hidden. The animatability of positive and negative spatial relationships brings interesting transition effects.

clip-path comes with four shapes and can use URL to link external SVGs<clippath></clippath> element. Here are examples of the first four shapes:

shape	Example	result
Circular	clip-path: circle(25% at 25% 25%);
Oval	clip-path: ellipse(25% 50% at 25% 50%);
Inline	clip-path: inset(10% 20% 30% 40% round 25%);
Polygons	clip-path: polygon(50% 25%, 75% 75%, 25% 75%);

Combined with CSS transition animation

clip-path animation can be used to change attribute values ​​to achieve the conversion between shapes through CSS transition, and the triggering method can be class switching or interactive state changes in JavaScript (for example :hover ).

 .box {
  clip-path: circle(75%);
  transition: clip-path 1s;
}

.box:hover {
  clip-path: circle(25%);
}

CSS animations can also be used:

 @keyframes circle {
  0% { clip-path: circle(75%); }
  100% { clip-path: circle(25%); }
}

The following points should be paid attention to when clip-path animation:

• It only affects the rendered content and does not change the box size of the element. For example, a floating box and its surrounding text, even if a small clip-path is applied, the space it takes up remains unchanged.
• Any CSS attributes that exceed the size of the element box may be clipped. For example, inset with all 0% in all four directions will remove box-shadow and need to use a negative percentage to see the shadow. But this can also produce interesting visuals in itself!

Next, let's look at some simple animation examples.

Simple shape comparison

The following example shows the animation effects of each shape and its description. The example uses Vue.js, but the CSS part is easy to port to other projects.

Circular

 clip-path: circle(<length> at<position> );</position></length>

Circles accept two animated properties:

1. Shape Radius: Can be length or percentage
2. Position: can be the length or percentage on the x-axis and y-axis

 .circle-enter-active { animation: 1s circle reverse; }
.circle-leave-active { animation: 1s circle; }

@keyframes circle {
  0% { clip-path: circle(75%); }
  100% { clip-path: circle(0%); }
}

Oval

 clip-path: ellipse(<length> {2} at<position> );</position></length>

The oval accepts three animated properties:

1. Horizontal Radius: Can be length or percentage
2. Vertical radius: can be length or percentage
3. Position: can be the length or percentage on the x-axis and y-axis

 .ellipse-enter-active { animation: 1s ellipse reverse; }
.ellipse-leave-active { animation: 1s ellipse; }

@keyframes ellipse {
  0% { clip-path: ellipse(80% 80%); }
  100% { clip-path: ellipse(0% 20%); }
}

Inline

 clip-path: inset(<length> {1,4} round<border-radius> {1,4});</border-radius></length>

There are up to five animated properties for embedded shapes. The first four represent each edge of the shape, similar to margins or padding. The first property is required, and the remaining three are optional, depending on the desired shape.

1. Length/percent: can represent all four sides, two sides, or upper edge
2. Length/percent: can represent the left and right sides or right sides
3. Length/percent: indicates the following
4. Length/percent: indicates the left side
5. Round corners: Need to use the "round" keyword before the value

It should be noted that using values ​​is the opposite of typical CSS usage. Defining an edge as zero means there is no change and the shape is pushed outward to the edge of the element. As the value increases (for example to 10%), the edges of the shape push inward toward the edges of the element.

 .inset-enter-active { animation: 1s inset reverse; }
.inset-leave-active { animation: 1s inset; }

@keyframes inset {
  0% { clip-path: inset(0% round 0%); }
  100% { clip-path: inset(50% round 50%); }
}

Polygons

 clip-path: polygon(<length> );</length>

Polygon shapes are special in animated properties. Each attribute represents a vertex of a shape, requiring at least three. The number of more than three vertices is limited only by the desired shape. For each keyframe or two steps of the animation, the vertex number must always match to achieve smooth animation. Changes in vertex count can be animated, but will cause pop-up effects at each keyframe.

 .polygon-enter-active { animation: 1s polygon reverse; }
.polygon-leave-active { animation: 1s polygon; }

@keyframes polygon {
  0% { clip-path: polygon(0 0, 50% 0, 100% 0, 100% 50%, 100% 100%, 50% 100%, 0 100%, 0 50%); }
  100% { clip-path: polygon(50% 50%, 50% 25%, 50% 50%, 75% 50%, 50% 50%, 50% 75%, 50% 50%, 25% 50%); }
}

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