How to draw triangles and parallelograms with CSS

Recently I have seen many tutorials on the Internet teaching you how to use CSS to draw graphics. Today I will summarize for you how to use CSS style sheets to draw triangles and parallelograms. Those who are interested can study it in depth.

The first method: use border

A rectangle to join two triangles to finally create a parallelogram. Why can triangles be generated using borders? Let’s take a look at a picture first:

After looking at the changing process of the three small figures in the picture, you should already understand half of it. In fact, hacking only requires two conditions to create a triangle. First, the length and width of the element itself are 0; second, the unnecessary parts are hidden through border-color. Through a similar method, you can also create trapezoids. The code for the three shapes in the above picture is as follows. (Attached is a CodePen example, http://codepen.io/jerryzou/pen/mJYJym)

#first {
  width: 20px;
  height: 20px;
  border-width: 10px;
  border-style: solid;
  border-color: red green blue brown;
}

#second {
  width: 0;
  height: 0;
  border-width: 10px;
  border-style: solid;
  border-color: red green blue brown;
}

#third {
  width: 0;
  height: 0;
  border-width: 10px;
  border-style: solid;
  border-color: red transparent transparent transparent;
}

The next step is to consider how to splice a parallelogram. In the border method, it consists of three parts, namely the left triangle, the rectangle, and the right triangle. It would be too cumbersome to create three elements every time a parallelogram is drawn, so the :before and :after pseudo-elements are a good choice here. Let's achieve this effect:

In order to seamlessly splice triangles and rectangles together, multiple attributes must be consistent, so use something like Less, Sass , Stylus and other CSS preprocessors will make this code easier to maintain. The Scss version of the code is given below. (Attached is the CodePen link, http://codepen.io/jerryzou/pen/ZGNGWZ?editors=110)

//三角形的宽高
$height: 24px;
$width: 12px;

//对平行四边形三部分的颜色进行赋值
@mixin parallelogram-color($color) {
  background: $color;
  &:before { border-color: transparent $color $color transparent; }
  &:after { border-color: $color transparent transparent $color; }
}

//单个三角形的样式
@mixin triangle() {
  content: '';
  display: block;
  width: 0;
  height: 0;
  position: absolute;
  border-style: solid;
  border-width: $height/2 $width/2;
  top: 0;
}

//平行四边形的样式
.para {
  display: inline-block;
  position: relative;
  padding: 0 10px;
  height: $height;
  line-height: $height;
  margin-left: $width;
  color: #fff;

  &:after {
    @include triangle();
    right: -$width;
  }

  &:before {
    @include triangle();
    left: -$width;
  }

  @include parallelogram-color(red);
}

It should be noted that if the slope of the triangle set by $height and $width is too small or If it is too large, it may cause jagged rendering, so you need to test the visual effects of different widths and heights when using it.

The second method: using transform

The method of using transform to realize parallelogram is what I saw when I was shopping, the effect is about It looks like this:

After seeing it, I thought it was so amazing. It turns out that it can only have the outer outline of a parallelogram. (Because method one can only create a parallelogram with a filling effect) It is very simple to implement, mainly with the help of transform: skew(...). Let’s take a look at the source code.

<style>
.city {
  display: inline-block;
  padding: 5px 20px;
  border: 1px solid #44a5fc;
  color: #333;
  transform: skew(-20deg);
}
</style>

<div class="city">上海</div>

So we got this effect:

You must think this when you see the picture:

Don’t worry, we have indeed distorted the entire div, causing the text in the middle to be slanted, and this is obviously not the effect we want. So we need to add an inner element and reversely distort the inner element to get the effect we want:

The implementation code is as follows, Attached is a CodePen example (http://codepen.io/jerryzou/pen/BNeNwV?editors=110)

<style>
.city {
  display: inline-block;
  padding: 5px 20px;
  border: 1px solid #44a5fc;
  color: #333;
  transform: skew(-20deg);
}

.city div {
  transform: skew(20deg);
}
</style>

<div class="city">
  <div>上海</div>
</div>

Summary

The first method uses the border attribute to hack out the triangle and pass Splicing three elements finally achieves a parallelogram; while the second method uses transform: skew to obtain a parallelogram. Overall, the second method is much smaller than the first method and is easy to understand. The only drawback is that it cannot construct trapezoids like those used in the pagination of this site.

I hope this article will be helpful to everyone. In fact, the same principle applies. Squares, rectangles and some equilateral figures can also be made using this method.

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