mirror of
https://github.com/gopl-zh/gopl-zh.github.com.git
synced 2024-11-24 15:18:57 +00:00
356 lines
36 KiB
HTML
356 lines
36 KiB
HTML
|
<!DOCTYPE HTML>
|
|||
|
|
<html lang="zh" class="sidebar-visible no-js light">
|
|||
|
|
<head>
|
|||
|
|
<!-- Book generated using mdBook -->
|
|||
|
|
<meta charset="UTF-8">
|
|||
|
|
<title>浮点数 - Go语言圣经</title>
|
|||
|
|
|
|||
|
|
|
|||
|
|
<!-- Custom HTML head -->
|
|||
|
|
|
|||
|
|
|
|||
|
|
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
|
|||
|
|
<meta name="description" content="<The Go Programming Language>中文版">
|
|||
|
|
<meta name="viewport" content="width=device-width, initial-scale=1">
|
|||
|
|
<meta name="theme-color" content="#ffffff" />
|
|||
|
|
|
|||
|
|
<link rel="icon" href="../favicon.svg">
|
|||
|
|
<link rel="shortcut icon" href="../favicon.png">
|
|||
|
|
<link rel="stylesheet" href="../css/variables.css">
|
|||
|
|
<link rel="stylesheet" href="../css/general.css">
|
|||
|
|
<link rel="stylesheet" href="../css/chrome.css">
|
|||
|
|
<link rel="stylesheet" href="../css/print.css" media="print">
|
|||
|
|
|
|||
|
|
<!-- Fonts -->
|
|||
|
|
<link rel="stylesheet" href="../FontAwesome/css/font-awesome.css">
|
|||
|
|
<link rel="stylesheet" href="../fonts/fonts.css">
|
|||
|
|
|
|||
|
|
<!-- Highlight.js Stylesheets -->
|
|||
|
|
<link rel="stylesheet" href="../highlight.css">
|
|||
|
|
<link rel="stylesheet" href="../tomorrow-night.css">
|
|||
|
|
<link rel="stylesheet" href="../ayu-highlight.css">
|
|||
|
|
|
|||
|
|
<!-- Custom theme stylesheets -->
|
|||
|
|
<link rel="stylesheet" href="../style.css">
|
|||
|
|
|
|||
|
|
|
|||
|
|
</head>
|
|||
|
|
<body>
|
|||
|
|
<!-- Provide site root to javascript -->
|
|||
|
|
<script type="text/javascript">
|
|||
|
|
var path_to_root = "../";
|
|||
|
|
var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "navy" : "light";
|
|||
|
|
</script>
|
|||
|
|
|
|||
|
|
<!-- Work around some values being stored in localStorage wrapped in quotes -->
|
|||
|
|
<script type="text/javascript">
|
|||
|
|
try {
|
|||
|
|
var theme = localStorage.getItem('mdbook-theme');
|
|||
|
|
var sidebar = localStorage.getItem('mdbook-sidebar');
|
|||
|
|
|
|||
|
|
if (theme.startsWith('"') && theme.endsWith('"')) {
|
|||
|
|
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
if (sidebar.startsWith('"') && sidebar.endsWith('"')) {
|
|||
|
|
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
|
|||
|
|
}
|
|||
|
|
} catch (e) { }
|
|||
|
|
</script>
|
|||
|
|
|
|||
|
|
<!-- Set the theme before any content is loaded, prevents flash -->
|
|||
|
|
<script type="text/javascript">
|
|||
|
|
var theme;
|
|||
|
|
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
|
|||
|
|
if (theme === null || theme === undefined) { theme = default_theme; }
|
|||
|
|
var html = document.querySelector('html');
|
|||
|
|
html.classList.remove('no-js')
|
|||
|
|
html.classList.remove('light')
|
|||
|
|
html.classList.add(theme);
|
|||
|
|
html.classList.add('js');
|
|||
|
|
</script>
|
|||
|
|
|
|||
|
|
<!-- Hide / unhide sidebar before it is displayed -->
|
|||
|
|
<script type="text/javascript">
|
|||
|
|
var html = document.querySelector('html');
|
|||
|
|
var sidebar = 'hidden';
|
|||
|
|
if (document.body.clientWidth >= 1080) {
|
|||
|
|
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
|
|||
|
|
sidebar = sidebar || 'visible';
|
|||
|
|
}
|
|||
|
|
html.classList.remove('sidebar-visible');
|
|||
|
|
html.classList.add("sidebar-" + sidebar);
|
|||
|
|
</script>
|
|||
|
|
|
|||
|
|
<nav id="sidebar" class="sidebar" aria-label="Table of contents">
|
|||
|
|
<div class="sidebar-scrollbox">
|
|||
|
|
<ol class="chapter"><li class="chapter-item expanded affix "><a href="../index.html">Go语言圣经</a></li><li class="chapter-item expanded affix "><a href="../preface.html">前言</a></li><li class="chapter-item expanded "><a href="../ch1/ch1.html"><strong aria-hidden="true">1.</strong> 入门</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../ch1/ch1-01.html"><strong aria-hidden="true">1.1.</strong> Hello, World</a></li><li class="chapter-item expanded "><a href="../ch1/ch1-02.html"><strong aria-hidden="true">1.2.</strong> 命令行参数</a></li><li class="chapter-item expanded "><a href="../ch1/ch1-03.html"><strong aria-hidden="true">1.3.</strong> 查找重复的行</a></li><li class="chapter-item expanded "><a href="../ch1/ch1-04.html"><strong aria-hidden="true">1.4.</strong> GIF动画</a></li><li class="chapter-item expanded "><a href="../ch1/ch1-05.html"><strong aria-hidden="true">1.5.</strong> 获取URL</a></li><li class="chapter-item expanded "><a href="../ch1/ch1-06.html"><strong aria-hidden="true">1.6.</strong> 并发获取多个URL</a></li><li class="chapter-item expanded "><a href="../ch1/ch1-07.html"><strong aria-hidden="true">1.7.</strong> Web服务</a></li><li class="chapter-item expanded "><a href="../ch1/ch1-08.html"><strong aria-hidden="true">1.8.</strong> 本章要点</a></li></ol></li><li class="chapter-item expanded "><a href="../ch2/ch2.html"><strong aria-hidden="true">2.</strong> 程序结构</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../ch2/ch2-01.html"><strong aria-hidden="true">2.1.</strong> 命名</a></li><li class="chapter-item expanded "><a href="../ch2/ch2-02.html"><strong aria-hidden="true">2.2.</strong> 声明</a></li><li class="chapter-item expanded "><a href="../ch2/ch2-03.html"><strong aria-hidden="true">2.3.</strong> 变量</a></li><li class="chapter-item expanded "><a href="../ch2/ch2-04.html"><strong aria-hidden="true">2.4.</strong> 赋值</a></li><li class="chapter-item expanded "><a href="../ch2/ch2-05.html"><strong aria-hidden="true">2.5.</strong> 类型</a></li><li class="chapter-item expanded "><a href="../ch2/ch2-06.html"><strong aria-hidden="true">2.6.</strong> 包和文件</a></li><li class="chapter-item expanded "><a href="../ch2/ch2-07.html"><strong aria-hidden="true">2.7.</strong> 作用域</a></li></ol></li><li class="chapter-item expanded "><a href="../ch3/ch3.html"><strong aria-hidden="true">3.</strong> 基础数据类型</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../ch3/ch3-01.html"><strong aria-hidden="true">3.1.</strong> 整型</a></li><li class="chapter-item expanded "><a href="../ch3/ch3-02.html" class="active"><strong aria-hidden="true">3.2.</strong> 浮点数</a></li><li class="chapter-item expanded "><a href="../ch3/ch3-03.html"><strong aria-hidden="true">3.3.</strong> 复数</a></li><li class="chapter-item expanded "><a href="../ch3/ch3-04.html"><strong aria-hidden="true">3.4.</strong> 布尔型</a></li><li class="chapter-item expanded "><a href="../ch3/ch3-05.html"><strong aria-hidden="true">3.5.</strong> 字符串</a></li><li class="chapter-item expanded "><a href="../ch3/ch3-06.html"><strong aria-hidden="true">3.6.</strong> 常量</a></li></ol></li><li class="chapter-item expanded "><a href="../ch4/ch4.html"><strong aria-hidden="true">4.</strong> 复合数据类型</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../ch4/ch4-01.html"><strong aria-hidden="true">4.1.</strong> 数组</a></li><li class="chapter-item expanded "><a href="../ch4/ch4-02.html"><strong aria-hidden="true">4.2.</strong> Slice</a></li><li class="chapter-item expanded "><a href="../ch4/ch4-03.html"><strong aria-hidden="true">4.3.</strong> Map</a></li><li class="chapter-item expanded "><a href="../ch4/ch4-04.html"><strong aria-hidden="true">4.4.</strong> 结构体</a></li><li class="chapter-item expanded "><a href="../ch4/ch4-05.html"><strong aria-hidden="true">4.5.</strong> JSON</a></li><li class="chapter-item expanded "><a href="../ch4/ch4-06.html"><s
|
|||
|
|
<div id="sidebar-resize-handle" class="sidebar-resize-handle"></div>
|
|||
|
|
</nav>
|
|||
|
|
|
|||
|
|
<div id="page-wrapper" class="page-wrapper">
|
|||
|
|
|
|||
|
|
<div class="page">
|
|||
|
|
|
|||
|
|
<div id="menu-bar-hover-placeholder"></div>
|
|||
|
|
<div id="menu-bar" class="menu-bar sticky bordered">
|
|||
|
|
<div class="left-buttons">
|
|||
|
|
<button id="sidebar-toggle" class="icon-button" type="button" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
|
|||
|
|
<i class="fa fa-bars"></i>
|
|||
|
|
</button>
|
|||
|
|
<button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
|
|||
|
|
<i class="fa fa-paint-brush"></i>
|
|||
|
|
</button>
|
|||
|
|
<ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
|
|||
|
|
<li role="none"><button role="menuitem" class="theme" id="light">Light (default)</button></li>
|
|||
|
|
<li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
|
|||
|
|
<li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
|
|||
|
|
<li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
|
|||
|
|
<li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
|
|||
|
|
</ul>
|
|||
|
|
<button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
|
|||
|
|
<i class="fa fa-search"></i>
|
|||
|
|
</button>
|
|||
|
|
</div>
|
|||
|
|
|
|||
|
|
<h1 class="menu-title">Go语言圣经</h1>
|
|||
|
|
|
|||
|
|
<div class="right-buttons">
|
|||
|
|
<a href="../print.html" title="Print this book" aria-label="Print this book">
|
|||
|
|
<i id="print-button" class="fa fa-print"></i>
|
|||
|
|
</a>
|
|||
|
|
<a href="https://github.com/gopl-zh/gopl-zh.github.com" title="Git repository" aria-label="Git repository">
|
|||
|
|
<i id="git-repository-button" class="fa fa-github"></i>
|
|||
|
|
</a>
|
|||
|
|
<a href="https://github.com/gopl-zh/gopl-zh.github.com/edit/master/./ch3/ch3-02.md" title="Suggest an edit" aria-label="Suggest an edit">
|
|||
|
|
<i id="git-edit-button" class="fa fa-edit"></i>
|
|||
|
|
</a>
|
|||
|
|
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
|
|||
|
|
<div id="search-wrapper" class="hidden">
|
|||
|
|
<form id="searchbar-outer" class="searchbar-outer">
|
|||
|
|
<input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
|
|||
|
|
</form>
|
|||
|
|
<div id="searchresults-outer" class="searchresults-outer hidden">
|
|||
|
|
<div id="searchresults-header" class="searchresults-header"></div>
|
|||
|
|
<ul id="searchresults">
|
|||
|
|
</ul>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
|
|||
|
|
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
|
|||
|
|
<script type="text/javascript">
|
|||
|
|
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
|
|||
|
|
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
|
|||
|
|
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
|
|||
|
|
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
|
|||
|
|
});
|
|||
|
|
</script>
|
|||
|
|
|
|||
|
|
<div id="content" class="content">
|
|||
|
|
<!-- Page table of contents -->
|
|||
|
|
<div class="sidetoc"><nav class="pagetoc"></nav></div>
|
|||
|
|
<main>
|
|||
|
|
<!-- 头部 -->
|
|||
|
|
<ul dir="auto">
|
|||
|
|
<li><em>KusonStack一站式可编程配置技术栈: <a href="https://github.com/KusionStack/kusion">https://github.com/KusionStack/kusion</a></em></li>
|
|||
|
|
<li><em>凹语言™: <a href="https://github.com/wa-lang/wa">https://github.com/wa-lang/wa</a></em></li>
|
|||
|
|
</ul>
|
|||
|
|
<hr>
|
|||
|
|
|
|||
|
|
<h2 id="32-浮点数"><a class="header" href="#32-浮点数">3.2. 浮点数</a></h2>
|
|||
|
|
<p>Go语言提供了两种精度的浮点数，float32和float64。它们的算术规范由IEEE754浮点数国际标准定义，该浮点数规范被所有现代的CPU支持。</p>
|
|||
|
|
<p>这些浮点数类型的取值范围可以从很微小到很巨大。浮点数的范围极限值可以在math包找到。常量math.MaxFloat32表示float32能表示的最大数值，大约是 3.4e38；对应的math.MaxFloat64常量大约是1.8e308。它们分别能表示的最小值近似为1.4e-45和4.9e-324。</p>
|
|||
|
|
<p>一个float32类型的浮点数可以提供大约6个十进制数的精度，而float64则可以提供约15个十进制数的精度；通常应该优先使用float64类型，因为float32类型的累计计算误差很容易扩散，并且float32能精确表示的正整数并不是很大（译注：因为float32的有效bit位只有23个，其它的bit位用于指数和符号；当整数大于23bit能表达的范围时，float32的表示将出现误差）：</p>
|
|||
|
|
<pre><code class="language-Go">var f float32 = 16777216 // 1 << 24
|
|||
|
|
fmt.Println(f == f+1) // "true"!
|
|||
|
|
</code></pre>
|
|||
|
|
<p>浮点数的字面值可以直接写小数部分，像这样：</p>
|
|||
|
|
<pre><code class="language-Go">const e = 2.71828 // (approximately)
|
|||
|
|
</code></pre>
|
|||
|
|
<p>小数点前面或后面的数字都可能被省略（例如.707或1.）。很小或很大的数最好用科学计数法书写，通过e或E来指定指数部分：</p>
|
|||
|
|
<pre><code class="language-Go">const Avogadro = 6.02214129e23 // 阿伏伽德罗常数
|
|||
|
|
const Planck = 6.62606957e-34 // 普朗克常数
|
|||
|
|
</code></pre>
|
|||
|
|
<p>用Printf函数的%g参数打印浮点数，将采用更紧凑的表示形式打印，并提供足够的精度，但是对应表格的数据，使用%e（带指数）或%f的形式打印可能更合适。所有的这三个打印形式都可以指定打印的宽度和控制打印精度。</p>
|
|||
|
|
<pre><code class="language-Go">for x := 0; x < 8; x++ {
|
|||
|
|
fmt.Printf("x = %d e^x = %8.3f\n", x, math.Exp(float64(x)))
|
|||
|
|
}
|
|||
|
|
</code></pre>
|
|||
|
|
<p>上面代码打印e的幂，打印精度是小数点后三个小数精度和8个字符宽度：</p>
|
|||
|
|
<pre><code>x = 0 e^x = 1.000
|
|||
|
|
x = 1 e^x = 2.718
|
|||
|
|
x = 2 e^x = 7.389
|
|||
|
|
x = 3 e^x = 20.086
|
|||
|
|
x = 4 e^x = 54.598
|
|||
|
|
x = 5 e^x = 148.413
|
|||
|
|
x = 6 e^x = 403.429
|
|||
|
|
x = 7 e^x = 1096.633
|
|||
|
|
</code></pre>
|
|||
|
|
<p>math包中除了提供大量常用的数学函数外，还提供了IEEE754浮点数标准中定义的特殊值的创建和测试：正无穷大和负无穷大，分别用于表示太大溢出的数字和除零的结果；还有NaN非数，一般用于表示无效的除法操作结果0/0或Sqrt(-1).</p>
|
|||
|
|
<pre><code class="language-Go">var z float64
|
|||
|
|
fmt.Println(z, -z, 1/z, -1/z, z/z) // "0 -0 +Inf -Inf NaN"
|
|||
|
|
</code></pre>
|
|||
|
|
<p>函数math.IsNaN用于测试一个数是否是非数NaN，math.NaN则返回非数对应的值。虽然可以用math.NaN来表示一个非法的结果，但是测试一个结果是否是非数NaN则是充满风险的，因为NaN和任何数都是不相等的（译注：在浮点数中，NaN、正无穷大和负无穷大都不是唯一的，每个都有非常多种的bit模式表示）：</p>
|
|||
|
|
<pre><code class="language-Go">nan := math.NaN()
|
|||
|
|
fmt.Println(nan == nan, nan < nan, nan > nan) // "false false false"
|
|||
|
|
</code></pre>
|
|||
|
|
<p>如果一个函数返回的浮点数结果可能失败，最好的做法是用单独的标志报告失败，像这样：</p>
|
|||
|
|
<pre><code class="language-Go">func compute() (value float64, ok bool) {
|
|||
|
|
// ...
|
|||
|
|
if failed {
|
|||
|
|
return 0, false
|
|||
|
|
}
|
|||
|
|
return result, true
|
|||
|
|
}
|
|||
|
|
</code></pre>
|
|||
|
|
<p>接下来的程序演示了通过浮点计算生成的图形。它是带有两个参数的z = f(x, y)函数的三维形式，使用了可缩放矢量图形（SVG）格式输出，SVG是一个用于矢量线绘制的XML标准。图3.1显示了sin(r)/r函数的输出图形，其中r是<code>sqrt(x*x+y*y)</code>。</p>
|
|||
|
|
<p><img src="../images/ch3-01.png" alt="" /></p>
|
|||
|
|
<p><u><i>gopl.io/ch3/surface</i></u></p>
|
|||
|
|
<pre><code class="language-Go">// Surface computes an SVG rendering of a 3-D surface function.
|
|||
|
|
package main
|
|||
|
|
|
|||
|
|
import (
|
|||
|
|
"fmt"
|
|||
|
|
"math"
|
|||
|
|
)
|
|||
|
|
|
|||
|
|
const (
|
|||
|
|
width, height = 600, 320 // canvas size in pixels
|
|||
|
|
cells = 100 // number of grid cells
|
|||
|
|
xyrange = 30.0 // axis ranges (-xyrange..+xyrange)
|
|||
|
|
xyscale = width / 2 / xyrange // pixels per x or y unit
|
|||
|
|
zscale = height * 0.4 // pixels per z unit
|
|||
|
|
angle = math.Pi / 6 // angle of x, y axes (=30°)
|
|||
|
|
)
|
|||
|
|
|
|||
|
|
var sin30, cos30 = math.Sin(angle), math.Cos(angle) // sin(30°), cos(30°)
|
|||
|
|
|
|||
|
|
func main() {
|
|||
|
|
fmt.Printf("<svg xmlns='http://www.w3.org/2000/svg' "+
|
|||
|
|
"style='stroke: grey; fill: white; stroke-width: 0.7' "+
|
|||
|
|
"width='%d' height='%d'>", width, height)
|
|||
|
|
for i := 0; i < cells; i++ {
|
|||
|
|
for j := 0; j < cells; j++ {
|
|||
|
|
ax, ay := corner(i+1, j)
|
|||
|
|
bx, by := corner(i, j)
|
|||
|
|
cx, cy := corner(i, j+1)
|
|||
|
|
dx, dy := corner(i+1, j+1)
|
|||
|
|
fmt.Printf("<polygon points='%g,%g %g,%g %g,%g %g,%g'/>\n",
|
|||
|
|
ax, ay, bx, by, cx, cy, dx, dy)
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
fmt.Println("</svg>")
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
func corner(i, j int) (float64, float64) {
|
|||
|
|
// Find point (x,y) at corner of cell (i,j).
|
|||
|
|
x := xyrange * (float64(i)/cells - 0.5)
|
|||
|
|
y := xyrange * (float64(j)/cells - 0.5)
|
|||
|
|
|
|||
|
|
// Compute surface height z.
|
|||
|
|
z := f(x, y)
|
|||
|
|
|
|||
|
|
// Project (x,y,z) isometrically onto 2-D SVG canvas (sx,sy).
|
|||
|
|
sx := width/2 + (x-y)*cos30*xyscale
|
|||
|
|
sy := height/2 + (x+y)*sin30*xyscale - z*zscale
|
|||
|
|
return sx, sy
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
func f(x, y float64) float64 {
|
|||
|
|
r := math.Hypot(x, y) // distance from (0,0)
|
|||
|
|
return math.Sin(r) / r
|
|||
|
|
}
|
|||
|
|
</code></pre>
|
|||
|
|
<p>要注意的是corner函数返回了两个结果，分别对应每个网格顶点的坐标参数。</p>
|
|||
|
|
<p>要解释这个程序是如何工作的需要一些基本的几何学知识，但是我们可以跳过几何学原理，因为程序的重点是演示浮点数运算。程序的本质是三个不同的坐标系中映射关系，如图3.2所示。第一个是100x100的二维网格，对应整数坐标(i,j)，从远处的(0,0)位置开始。我们从远处向前面绘制，因此远处先绘制的多边形有可能被前面后绘制的多边形覆盖。</p>
|
|||
|
|
<p>第二个坐标系是一个三维的网格浮点坐标(x,y,z)，其中x和y是i和j的线性函数，通过平移转换为网格单元的中心，然后用xyrange系数缩放。高度z是函数f(x,y)的值。</p>
|
|||
|
|
<p>第三个坐标系是一个二维的画布，起点(0,0)在左上角。画布中点的坐标用(sx,sy)表示。我们使用等角投影将三维点(x,y,z)投影到二维的画布中。</p>
|
|||
|
|
<p><img src="../images/ch3-02.png" alt="" /></p>
|
|||
|
|
<p>画布中从远处到右边的点对应较大的x值和较大的y值。并且画布中x和y值越大，则对应的z值越小。x和y的垂直和水平缩放系数来自30度角的正弦和余弦值。z的缩放系数0.4，是一个任意选择的参数。</p>
|
|||
|
|
<p>对于二维网格中的每一个网格单元，main函数计算单元的四个顶点在画布中对应多边形ABCD的顶点，其中B对应(i,j)顶点位置，A、C和D是其它相邻的顶点，然后输出SVG的绘制指令。</p>
|
|||
|
|
<p><strong>练习 3.1：</strong> 如果f函数返回的是无限制的float64值，那么SVG文件可能输出无效的<polygon>多边形元素（虽然许多SVG渲染器会妥善处理这类问题）。修改程序跳过无效的多边形。</p>
|
|||
|
|
<p><strong>练习 3.2：</strong> 试验math包中其他函数的渲染图形。你是否能输出一个egg box、moguls或a saddle图案?</p>
|
|||
|
|
<p><strong>练习 3.3：</strong> 根据高度给每个多边形上色，那样峰值部将是红色（#ff0000），谷部将是蓝色（#0000ff）。</p>
|
|||
|
|
<p><strong>练习 3.4：</strong> 参考1.7节Lissajous例子的函数，构造一个web服务器，用于计算函数曲面然后返回SVG数据给客户端。服务器必须设置Content-Type头部：</p>
|
|||
|
|
<pre><code class="language-Go">w.Header().Set("Content-Type", "image/svg+xml")
|
|||
|
|
</code></pre>
|
|||
|
|
<p>（这一步在Lissajous例子中不是必须的，因为服务器使用标准的PNG图像格式，可以根据前面的512个字节自动输出对应的头部。）允许客户端通过HTTP请求参数设置高度、宽度和颜色等参数。</p>
|
|||
|
|
|
|||
|
|
|
|||
|
|
<!-- 公众号 -->
|
|||
|
|
<hr>
|
|||
|
|
<table>
|
|||
|
|
<tr>
|
|||
|
|
<td>
|
|||
|
|
<img width="222px" src="https://chai2010.cn/advanced-go-programming-book/css.png">
|
|||
|
|
</td>
|
|||
|
|
<td>
|
|||
|
|
<img width="222px" src="https://chai2010.cn/advanced-go-programming-book/cch.png">
|
|||
|
|
</td>
|
|||
|
|
</tr>
|
|||
|
|
</table>
|
|||
|
|
|
|||
|
|
<div id="giscus-container"></div>
|
|||
|
|
<footer class="page-footer">
|
|||
|
|
<span>© 2015-2016 | <a href="https://github.com/gopl-zh"> Go语言圣经中文版</a>, 仅学习交流使用</span>
|
|||
|
|
</footer>
|
|||
|
|
</main>
|
|||
|
|
|
|||
|
|
<nav class="nav-wrapper" aria-label="Page navigation">
|
|||
|
|
<!-- Mobile navigation buttons -->
|
|||
|
|
<a rel="prev" href="../ch3/ch3-01.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
|||
|
|
<i class="fa fa-angle-left"></i>
|
|||
|
|
</a>
|
|||
|
|
|
|||
|
|
<a rel="next" href="../ch3/ch3-03.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
|||
|
|
<i class="fa fa-angle-right"></i>
|
|||
|
|
</a>
|
|||
|
|
|
|||
|
|
<div style="clear: both"></div>
|
|||
|
|
</nav>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
|
|||
|
|
<nav class="nav-wide-wrapper" aria-label="Page navigation">
|
|||
|
|
<a rel="prev" href="../ch3/ch3-01.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
|||
|
|
<i class="fa fa-angle-left"></i>
|
|||
|
|
</a>
|
|||
|
|
|
|||
|
|
<a rel="next" href="../ch3/ch3-03.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
|||
|
|
<i class="fa fa-angle-right"></i>
|
|||
|
|
</a>
|
|||
|
|
</nav>
|
|||
|
|
|
|||
|
|
</div>
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
<script type="text/javascript">
|
|||
|
|
window.playground_copyable = true;
|
|||
|
|
</script>
|
|||
|
|
|
|||
|
|
|
|||
|
|
<script src="../elasticlunr.min.js" type="text/javascript" charset="utf-8"></script>
|
|||
|
|
<script src="../mark.min.js" type="text/javascript" charset="utf-8"></script>
|
|||
|
|
<script src="../searcher.js" type="text/javascript" charset="utf-8"></script>
|
|||
|
|
|
|||
|
|
<script src="../clipboard.min.js" type="text/javascript" charset="utf-8"></script>
|
|||
|
|
<script src="../highlight.js" type="text/javascript" charset="utf-8"></script>
|
|||
|
|
<script src="../book.js" type="text/javascript" charset="utf-8"></script>
|
|||
|
|
<script type="text/javascript" charset="utf-8">
|
|||
|
|
var pagePath = "ch3/ch3-02.md"
|
|||
|
|
</script>
|
|||
|
|
|
|||
|
|
|
|||
|
|
<!-- Custom JS scripts -->
|
|||
|
|
<script type="text/javascript" src="../js/custom.js"></script>
|
|||
|
|
<script type="text/javascript" src="../js/bigPicture.js"></script>
|
|||
|
|
|
|||
|
|
|
|||
|
|
</body>
|
|||
|
|
</html>
|