用CSS3 Region和3D变换实现书籍翻页效果

前言：我曾在之前的分享里提到CSS3 Region（区域模块）的重要作用：实现更复杂的排版效果，实现更丰富的富文本体验。下文就是和此模块相关的实际应用，可以看到未来它将发挥出巨大的作用。

这一天终于到来：你开始对大段滚动的文字感到厌倦，并正在寻找一种新的格式，更加优雅，更加紧凑。它可以把长长的滚动条切分为整齐的页面并结合在一起。我把这个发明叫做“书”。

利用CSS3 Region（去CanIUse看看当前浏览器支持的情况，Chrome需要进入chrome://flags并激活CSS3 Region）和3D变换，我们终于可以在现代浏览器上实现先进的书籍效果。所有你需要的仅是几行JavaScript和一堆CSS。

让我们开始定义书籍结构。这本书由书页组成，而书页包括两面。每一面写满这本书的内容：

<div class="book">
        <div> <!-- first page -->
          <div> <!-- front cover -->
            <h1>My Fancy Book</h1>
          </div>
          <div> <!-- backside of cover -->
            <h1>By Me I. Myself</h1>
            <h2>2012 Bogus HTML Publishing Ltd</h2>
          </div>
        </div>
        <!-- content pages -->        
        <div>
          <!-- front side of page -->
          <div class="book-pages"></div>
          <!-- back side of page -->
          <div class="book-pages"></div>
        </div>
       <div>
          <div class="book-pages"></div>
          <div class="book-pages"></div>
        </div>
        <div>
          <div class="book-pages"></div>
          <div class="book-pages"></div>
        </div>
</div>

我们将使用CSS Region控制文字流入书页。但是我们需要先定义这本书的内容。

<span id="book-content">
  blah blah blah ...
</span>

现在书已经写完了，让我们开始定义CSS流。我使用“+”字符作为占位符替换-webkit或-moz这样的浏览器前缀：

#book-content {
  +flow-into: book-text-flow;
}
.book-pages {
  +flow-from: book-text-flow;
}

现在来自span#book-content的内容会转而显示到div.book-pages元素里。这本书现在看起来相当差劲。为了让它看起来更美，我们需要更多努力。

我们可能需要把HTML的结构转换为更类似于书籍的形式：

html {
  width: 100%;
  height: 100%;
}
body {
  /* The entire body is clickable area. Let the visitor know that. */
  cursor: pointer;
  width: 100%;
  height: 100%;
  /* Set the perspective transform for the page so that our book looks 3D. */
  +perspective: 800px;
  /* Use 3D for body, the book itself and the page containers. */
  +transform-style: preserve-3d;
}
.book {
  +transform-style: preserve-3d;
  position: absolute;
}
/* Page containers, contain the two sides of the page as children. */
.book > div {
  +transform-style: preserve-3d;
  position: absolute;
}
/* Both sides of a page. These are flat inside the page container, so no preserve-3d. */
.book > div > div {
  /* Fake some lighting with a gradient. */
  background: +linear-gradient(-45deg, #ffffff 0%, #e5e5e5 100%);
  width: 600px;
  height: 400px;
  overflow: hidden;
  /* Pad the page text a bit. */
  padding: 30px;
  padding-bottom: 80px;
}
/* Front of a page */
.book > div > div:first-child {
  /* The front side of a page should be slightly above the back of the page. */
  +transform: translate3d(0px, 0px, 0.02px);
  /* Add some extra padding for the gutter. */
  padding-left: 40px;
  /* Stylish border in the gutter for visual effect. */
  border-left: 2px solid #000;
}
/* Back of a page */
.book > div > div:last-child {
  /* The back side of a page is flipped. */
  +transform: rotateY(180deg);
  padding-right: 40px;
  border-right: 2px solid #000;
}
/* Front cover of the book */
.book > div:first-child > div:first-child {
  /* The covers have a different color. */
  background: +linear-gradient(-45deg, #8c9ccc 0%, #080f40 100%);
  /* Put a border around the cover to make it cover the pages. */
  border: 2px solid #000;
  /* And center the cover. */
  margin-left: -1px;
  margin-top: -1px;
}
/* Back cover of the book */
.book > div:last-child > div:last-child {
  background: +linear-gradient(-45deg, #8c9ccc 0%, #080f40 100%);
  border: 2px solid #000;
  margin-left: -1px;
  margin-top: -1px;
}

我们完成了书籍风格的HTML页面，下面要开始添加JS。我们必须要给这本平平的书一些合适的体积。为了增加体积，我们在Z轴上定位每一页。

(function() {
var books = document.querySelectorAll(".book");
for (var i = 0; i < books.length; i++) {
  var book = books[i];
  var pages = book.childNodes;
  for (var j = 0; j < pages.length; j++) {
    if (pages[j].tagName == "DIV") {
      setTransform(pages[j], "translate3d(0px, 0px, " + (-j) + "px)");
    }
  }
}
})();

下面的代码使我们的书页平滑的显示。

.book > div {
  +transition: 1s ease-in-out;
}

最后，为了自动翻页，我们需要绑定事件。

(function(){
	// Get all the pages.
	var pages = document.querySelectorAll(".book > div");
	var currentPage = 0;
	// Go to previous page when clicking on left side of window.
	// Go to the next page when clicking on the right side.
	window.onclick = function(ev) {
	  if (ev.clientX < window.innerWidth/2) {
	    previousPage();
	  } else {
	    nextPage();
	  }
	  ev.preventDefault();
	};
	var previousPage = function() {
	  if (currentPage > 0) {
	    currentPage--;
            // Rotate the page to closed position and move it to its place in the closed page stack.
	    setTransform(pages[currentPage], "translate3d(0px,0px," + (-currentPage) + "px) rotateY(0deg)");
	  }
	};
	var nextPage = function() {
	  if (currentPage < pages.length) {
            // Rotate the page to open position and move it to its place in the opened stack.
	    setTransform(pages[currentPage], "translate3d(0px,0px," + currentPage + "px) rotateY(-150deg)");
	    currentPage++;
	  }
	};
})();

最终，我们完成了这本“书”。

你可以在这里看到示例以及源代码。如果你的浏览器不支持CSS Region，这本书会惨不忍睹，此时你可以试试这个例子。

译自：http://updates.html5rocks.com/2012/07/Writing-a-flippable-book-using-CSS-Regions-and-3D-transforms

转载请注明：来自蒋宇捷的博客（http://blog.csdn.net/hfahe）