129 lines
10 KiB
HTML
129 lines
10 KiB
HTML
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<title>std::lerp</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_numeric_lerp skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>lerp</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-numeric.html">numeric</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-cmath.html"><cmath></a></code></div>
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<td></td>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">float</span> lerp<span class="br0">(</span> <span class="kw4">float</span> a, <span class="kw4">float</span> b, <span class="kw4">float</span> t <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">double</span> lerp<span class="br0">(</span> <span class="kw4">double</span> a, <span class="kw4">double</span> b, <span class="kw4">double</span> t <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">long</span> <span class="kw4">double</span> lerp<span class="br0">(</span> <span class="kw4">long</span> <span class="kw4">double</span> a, <span class="kw4">long</span> <span class="kw4">double</span> b, <span class="kw4">long</span> <span class="kw4">double</span> t <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<tr class="t-dcl t-since-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> Promoted lerp<span class="br0">(</span> Arithmetic1 a, Arithmetic2 b, Arithmetic3 t <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<div class="t-li1"><span class="t-li">1-3)</span> 计算 <span class="mjax" style="display:none">\(a+t(b−a)\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">a+t(b−a)</span> ，即 <code>a</code> 与 <code>b</code> 间参数为 <code>t</code> 的线性内插（或为外插，当 <code>t</code> 落在范围 <code>[0,1]</code> 外时）。</div>
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<div class="t-li1"><span class="t-li">4)</span> 所有 1-3) 所不覆盖的<a href="cpp-types-is_arithmetic.html">算术类型</a>参数的重载集或模板。。若任何参数拥有<a href="cpp-types-is_integral.html">整数类型</a>，则将它转型为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 。若任何其他参数为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> ，则返回类型为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> ，否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 。</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<td>a, b, t</td>
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<td>-</td>
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<td>浮点或<a href="cpp-types-is_integral.html">整数类型</a>值</td>
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</table>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p><span class="mjax" style="display:none">\(a+t(b−a)\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">a+t(b−a)</span></p>
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<p><code>isfinite(a) && isfinite(b)</code> 时，保证下列属性：</p>
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<ul>
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<li>若 <code>t == 0</code> ，则结果等于 <code>a</code> ；</li>
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<li>若 <code>t == 1</code> ，则结果等于 <code>b</code> ；</li>
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<li>若 <code>t >= 0 && t <= 1</code> ，则结果有限；</li>
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<li>若 <code>isfinite(t) && a == b</code> ，则结果等于 <code>a</code> ；</li>
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<li>若 <code>isfinite(t) || (!isnan(t) && b-a != 0)</code> ，则结果非 <code>NaN</code> 。</li>
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</ul>
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<p>令 <code>CMP(x,y)</code> 为若 <code>x > y</code> 则为 <code>1</code> ，若 <code>x < y</code> 则为 <code>-1</code> ，否则为 <code>0</code> 。对于任何 <code>t1</code> 与 <code>t2</code> ， <code>CMP(lerp(a, b, t2), lerp(a, b, t1))</code> 、 <code>CMP(t2, t1)</code> 与 <code>CMP(b, a)</code> 的积非负。（即 <code>lerp</code> 单调。）</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>包含 <code><math.h></code> 时 <code>lerp</code> 在全局命名空间可用，即使它不是 C 的一部分。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <cmath></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">float</span> a<span class="sy1">=</span><span class="nu17">10.0f</span>, b<span class="sy1">=</span><span class="nu17">20.0f</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"a="</span> <span class="sy1"><<</span> a <span class="sy1"><<</span> <span class="st0">", "</span> <span class="sy1"><<</span> <span class="st0">"b="</span> <span class="sy1"><<</span> b <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy1"><<</span> <span class="st0">"mid point="</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">lerp</span><span class="br0">(</span>a,b,<span class="nu17">0.5f</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy1"><<</span> <a href="cpp-io-manip-boolalpha.html"><span class="kw1764">std::<span class="me2">boolalpha</span></span></a> <span class="sy1"><<</span> <span class="br0">(</span>a <span class="sy1">==</span> std<span class="sy4">::</span><span class="me2">lerp</span><span class="br0">(</span>a,b,<span class="nu17">0.0f</span><span class="br0">)</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">' '</span>
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<span class="sy1"><<</span> <a href="cpp-io-manip-boolalpha.html"><span class="kw1764">std::<span class="me2">boolalpha</span></span></a> <span class="sy1"><<</span> <span class="br0">(</span>b <span class="sy1">==</span> std<span class="sy4">::</span><span class="me2">lerp</span><span class="br0">(</span>a,b,<span class="nu17">1.0f</span><span class="br0">)</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">a=10, b=20
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mid point=15
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true true</pre></div>
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</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<div class="t-dsc-member-div">
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<div><a href="cpp-numeric-midpoint.html"><span class="t-lines"><span>midpoint</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>两个数值或指针间的中点<br />
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<span class="t-mark">(函数模板)</span></td>
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</table>
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</div>
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<div class="visualClear"></div>
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