【LESS系列】三角形Mixins

又是一篇自 W3CPLUS 中转化而来的文章。

和 W3CPLUS 上的做法，在设计上最大的不同就在于，这里我用的是多个 Mixins 函数来实现。

先总结这种做法的特点：

需要额外的标签来实现，因此可以在同一容器中插入多个三角，并且支持低版本浏览器

使用 Mixins 函数名来区分不同的三角，每个 Mixins 函数固定包含4个参数，规律已经在代码注释中说明，还是很好掌握的

P 前缀开头的是名义私有 Mixins ，供库本身调用。虽然也能外部调用，但实际意义不大。

因为我不想用太多的参数来区分不同的三角，觉得用  Mixins 函数名来区分更为直观、好记，所以也没有用的名义私有 Mixins，而不是通过控制作用域来实现真正的私有 Mixins。

多个 Mixins 函数的实现方式还有个好处，就是每个 Mixins 函数的实现都很简单直观，没有很复杂的逻辑，所以阅读起来感觉也是相对轻松点。

功能不算特别丰富，但基本能满足日常对与三角的使用。如果想要 just mobile ，且不需要同一容器中插入多个三角，可以改造成伪元素版，相信这对 LESS Developer 来说并不是难事。

/* LESS triangle Mixins 代码，命名为triangle.less */
/*
triangle 系列 Mixins
Mixins 名称中的 left ，right ，top ，bottom 描述的是三角形中90度的那个角的指向
凡是带 P 前缀的 Mixins 函数，都是名义私有 Mixins 函数，虽然也能调用，但单独调用它并无实质意义...

参数说明:
@size【必传】
三角的大小

@color【必传】
三角的颜色

@offsetSide【必传】
调整位置的匹配模式
如果 Mixins 名称是以 top 或者 bottom 为结尾，那此参数就调整水平位置，对应取值分别为 left 或者 right
如果 Mixins 名称是以 left 或者 right 为结尾，那此参数就调整垂直位置，对应取值分别为 top 或者 bottom

@offset
三角的位置，根据 @offsetSide 参数的取值，以对应的 CSS 属性调整三角形的所在位置
*/
.P-triangle-el-simple(){
  display: block;
  width: 0;
  height: 0;
  position: absolute;
}

.P-triangle(@size){
  border: (@size / 2) solid transparent;
}

.P-triangle-border(left){
  border-color: transparent @color transparent transparent;
  border-left-width: 0;
}

.P-triangle-border(right){
  border-color: transparent transparent transparent @color;
  border-right-width: 0;
}

.P-triangle-border(top){
  border-color: transparent transparent @color transparent;
  border-top-width: 0;
}

.P-triangle-border(bottom){
  border-color: @color transparent transparent transparent;
  border-bottom-width: 0;
}

.P-triangle-border(leftTop){
  border-top: @size solid @color;
  border-left: 0 solid transparent;
}

.P-triangle-border(rightTop){
  border-top: @size solid @color;
  border-right: 0 solid transparent;
}

.P-triangle-border(leftBottom){
  border-bottom: @size solid @color;
  border-left: 0 solid transparent;
}

.P-triangle-border(rightBottom){
  border-bottom: @size solid @color;
  border-right: 0 solid transparent;
}



.triangle-left(@size, @color, top, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size);
  .P-triangle-border(left);
  right: 100%;
  top: @offset;
}

.triangle-left(@size, @color, bottom, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size);
  .P-triangle-border(left);
  right: 100%;
  bottom: @offset;
}

.triangle-inner-left(@size, @color, top, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size);
  .P-triangle-border(left);
  right: 0;
  top: @offset;
}

.triangle-inner-left(@size, @color, bottom, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size);
  .P-triangle-border(left);
  right: 0;
  bottom: @offset;
}

.triangle-right(@size, @color, top, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size);
  .P-triangle-border(right);
  left: 100%;
  top: @offset;
}

.triangle-right(@size, @color, bottom, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size);
  .P-triangle-border(right);
  left: 100%;
  bottom: @offset;
}

.triangle-inner-right(@size, @color, top, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size);
  .P-triangle-border(right);
  left: 0;
  top: @offset;
}

.triangle-inner-right(@size, @color, bottom, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size);
  .P-triangle-border(right);
  left: 0;
  bottom: @offset;
}

.triangle-top(@size, @color, left, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size);
  .P-triangle-border(top);
  bottom: 100%;
  left: @offset;
}

.triangle-top(@size, @color, right, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size);
  .P-triangle-border(top);
  bottom: 100%;
  right: @offset;
}

.triangle-inner-top(@size, @color, left, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size);
  .P-triangle-border(top);
  bottom: 0;
  left: @offset;
}

.triangle-inner-top(@size, @color, right, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size);
  .P-triangle-border(top);
  bottom: 0;
  right: @offset;
}

.triangle-bottom(@size, @color, left, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size);
  .P-triangle-border(bottom);
  top: 100%;
  left: @offset;
}

.triangle-bottom(@size, @color, right, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size);
  .P-triangle-border(bottom);
  top: 100%;
  right: @offset;
}

.triangle-inner-bottom(@size, @color, left, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size);
  .P-triangle-border(bottom);
  top: 0;
  left: @offset;
}

.triangle-inner-bottom(@size, @color, right, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size);
  .P-triangle-border(bottom);
  top: 0;
  right: @offset;
}

.triangle-left-top(@size, @color, left, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size * 2);
  .P-triangle-border(leftTop);
  top: 100%;
  left: @offset;
}

.triangle-left-top(@size, @color, right, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size * 2);
  .P-triangle-border(leftTop);
  top: 100%;
  right: @offset;
}

.triangle-inner-left-top(@size, @color, left, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size * 2);
  .P-triangle-border(leftTop);
  top: 0;
  left: @offset;
}

.triangle-inner-left-top(@size, @color, right, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size * 2);
  .P-triangle-border(leftTop);
  top: 0;
  right: @offset;
}

.triangle-right-top(@size, @color, left, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size * 2);
  .P-triangle-border(rightTop);
  top: 100%;
  left: @offset;
}

.triangle-right-top(@size, @color, right, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size * 2);
  .P-triangle-border(rightTop);
  top: 100%;
  right: @offset;
}

.triangle-inner-right-top(@size, @color, left, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size * 2);
  .P-triangle-border(rightTop);
  top: 0;
  left: @offset;
}

.triangle-inner-right-top(@size, @color, right, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size * 2);
  .P-triangle-border(rightTop);
  top: 0;
  right: @offset;
}

.triangle-left-bottom(@size, @color, left, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size * 2);
  .P-triangle-border(leftBottom);
  bottom: 100%;
  left: @offset;
}

.triangle-left-bottom(@size, @color, right, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size * 2);
  .P-triangle-border(leftBottom);
  bottom: 100%;
  right: @offset;
}

.triangle-inner-left-bottom(@size, @color, left, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size * 2);
  .P-triangle-border(leftBottom);
  bottom: 0;
  left: @offset;
}

.triangle-inner-left-bottom(@size, @color, right, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size * 2);
  .P-triangle-border(leftBottom);
  bottom: 0;
  right: @offset;
}

.triangle-right-bottom(@size, @color, left, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size * 2);
  .P-triangle-border(rightBottom);
  bottom: 100%;
  left: @offset;
}

.triangle-right-bottom(@size, @color, right, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size * 2);
  .P-triangle-border(rightBottom);
  bottom: 100%;
  right: @offset;
}

.triangle-inner-right-bottom(@size, @color, left, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size * 2);
  .P-triangle-border(rightBottom);
  bottom: 0;
  left: @offset;
}

.triangle-inner-right-bottom(@size, @color, right, @offset: 0){
  .P-triangle-el-simple();
  .P-triangle(@size * 2);
  .P-triangle-border(rightBottom);
  bottom: 0;
  right: @offset;
}

/* 实例要用到的LESS代码 */
@import "triangle.less";
body {
  background: #fff;
}
.wrap-a, .wrap-b{
  display: inline-block;
  background: #f36;
  margin: 20px;
  padding: 10px;
  width: 240px;
  height: 45px;
  line-height: 45px;
  color: #fff;
  text-align: center;
  position: relative;
}
.wrap-b{
  background: #ff0;
  color: #f36;
}

.top-l{
  .triangle-top(20px, #f36, left);
}
.left-b{
  .triangle-left(20px, #f36, bottom);
}
.bottom-r{
  .triangle-bottom(20px, #f36, right);
}
.right-t{
  .triangle-right(20px, #f36, top);
}
.top-r{
  .triangle-top(20px, #f36, right);
}
.left-t{
  .triangle-left(20px, #f36, top);
}
.bottom-l{
  .triangle-bottom(20px, #f36, left);
}
.right-b{
  .triangle-right(20px, #f36, bottom);
}

.top-i-l{
  .triangle-inner-top(20px, #f36, left);
}
.left-i-b{
  .triangle-inner-left(20px, #f36, bottom);
}
.bottom-i-r{
  .triangle-inner-bottom(20px, #f36, right);
}
.right-i-t{
  .triangle-inner-right(20px, #f36, top);
}
.top-i-r{
  .triangle-inner-top(20px, #f36, right);
}
.left-i-t{
  .triangle-inner-left(20px, #f36, top);
}
.bottom-i-l{
  .triangle-inner-bottom(20px, #f36, left);
}
.right-i-b{
  .triangle-inner-right(20px, #f36, bottom);
}

.leftTop-r{
  .triangle-left-top(20px, #f36, right);
}
.rightTop-l{
  .triangle-right-top(20px, #f36, left);
}
.leftBottom-r{
  .triangle-left-bottom(20px, #f36, right);
}
.rightBottom-l{
  .triangle-right-bottom(20px, #f36, left);
}
.leftTop-l{
  .triangle-left-top(20px, #f36, left);
}
.rightTop-r{
  .triangle-right-top(20px, #f36, right);
}
.leftBottom-l{
  .triangle-left-bottom(20px, #f36, left);
}
.rightBottom-r{
  .triangle-right-bottom(20px, #f36, right);
}

.leftTop-i-r{
  .triangle-inner-left-top(20px, #f36, right);
}
.rightTop-i-l{
  .triangle-inner-right-top(20px, #f36, left);
}
.leftBottom-i-r{
  .triangle-inner-left-bottom(20px, #f36, right);
}
.rightBottom-i-l{
  .triangle-inner-right-bottom(20px, #f36, left);
}
.leftTop-i-l{
  .triangle-inner-left-top(20px, #f36, left);
}
.rightTop-i-r{
  .triangle-inner-right-top(20px, #f36, right);
}
.leftBottom-i-l{
  .triangle-inner-left-bottom(20px, #f36, left);
}
.rightBottom-i-r{
  .triangle-inner-right-bottom(20px, #f36, right);
}

<!-- 实例要用到的HTML代码，引入的CSS是上面两个LESS编译生成出的CSS文件 -->
<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title>test</title>
    <link type="text/css" rel="stylesheet" href="test.css">
</head>
<body>
<div class="wrap-a">
    EL1
    <i class="top-r"></i>
    <i class="left-t"></i>
    <i class="bottom-l"></i>
    <i class="right-b"></i>
</div>

<div class="wrap-a">
    EL2
    <i class="top-l"></i>
    <i class="left-b"></i>
    <i class="bottom-r"></i>
    <i class="right-t"></i>
</div>

<div class="wrap-b">
    EL3
    <i class="top-i-r"></i>
    <i class="left-i-t"></i>
    <i class="bottom-i-l"></i>
    <i class="right-i-b"></i>
</div>

<div class="wrap-b">
    EL4
    <i class="top-i-l"></i>
    <i class="left-i-b"></i>
    <i class="bottom-i-r"></i>
    <i class="right-i-t"></i>
</div>

<div class="wrap-a">
    EL5
    <i class="leftTop-r"></i>
    <i class="rightTop-l"></i>
    <i class="leftBottom-r"></i>
    <i class="rightBottom-l"></i>
</div>

<div class="wrap-a">
    EL6
    <i class="leftTop-l"></i>
    <i class="rightTop-r"></i>
    <i class="leftBottom-l"></i>
    <i class="rightBottom-r"></i>
</div>

<div class="wrap-b">
    EL7
    <i class="leftTop-i-r"></i>
    <i class="rightTop-i-l"></i>
    <i class="leftBottom-i-r"></i>
    <i class="rightBottom-i-l"></i>
</div>

<div class="wrap-b">
    EL8
    <i class="leftTop-i-l"></i>
    <i class="rightTop-i-r"></i>
    <i class="leftBottom-i-l"></i>
    <i class="rightBottom-i-r"></i>
</div>
</body>
</html>

最后补一发效果图：