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</script></nav></div><div class="container mainContainer docsContainer"><div class="wrapper"><div class="post"><header class="postHeader"><a class="edit-page-link button" href="https://github.com/facebook/react-native-website/blob/master/docs/pixelratio.md" target="_blank" rel="noreferrer noopener">Edit</a><h1 id="__docusaurus" class="postHeaderTitle">PixelRatio</h1></header><article><div><span><p><code>PixelRatio</code> gives you access to the device's pixel density and font scale.</p>
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<h2><a class="anchor" aria-hidden="true" id="fetching-a-correctly-sized-image"></a><a href="#fetching-a-correctly-sized-image" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Fetching a correctly sized image</h2>
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<p>You should get a higher resolution image if you are on a high pixel density device. A good rule of thumb is to multiply the size of the image you display by the pixel ratio.</p>
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<pre><code class="hljs css language-jsx"><span class="token keyword">var</span> image <span class="token operator">=</span> <span class="token function">getImage</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
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width<span class="token punctuation">:</span> PixelRatio<span class="token punctuation">.</span><span class="token function">getPixelSizeForLayoutSize</span><span class="token punctuation">(</span><span class="token number">200</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
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height<span class="token punctuation">:</span> PixelRatio<span class="token punctuation">.</span><span class="token function">getPixelSizeForLayoutSize</span><span class="token punctuation">(</span><span class="token number">100</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
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<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token tag"><span class="token tag"><span class="token punctuation"><</span><span class="token class-name">Image</span></span> <span class="token attr-name">source</span><span class="token script language-javascript"><span class="token script-punctuation punctuation">=</span><span class="token punctuation">{</span>image<span class="token punctuation">}</span></span> <span class="token attr-name">style</span><span class="token script language-javascript"><span class="token script-punctuation punctuation">=</span><span class="token punctuation">{</span><span class="token punctuation">{</span>width<span class="token punctuation">:</span> <span class="token number">200</span><span class="token punctuation">,</span> height<span class="token punctuation">:</span> <span class="token number">100</span><span class="token punctuation">}</span><span class="token punctuation">}</span></span> <span class="token punctuation">/></span></span><span class="token punctuation">;</span>
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</code></pre>
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<h2><a class="anchor" aria-hidden="true" id="pixel-grid-snapping"></a><a href="#pixel-grid-snapping" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Pixel grid snapping</h2>
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<p>In iOS, you can specify positions and dimensions for elements with arbitrary precision, for example 29.674825. But, ultimately the physical display only have a fixed number of pixels, for example 640×960 for iPhone 4 or 750×1334 for iPhone 6. iOS tries to be as faithful as possible to the user value by spreading one original pixel into multiple ones to trick the eye. The downside of this technique is that it makes the resulting element look blurry.</p>
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<p>In practice, we found out that developers do not want this feature and they have to work around it by doing manual rounding in order to avoid having blurry elements. In React Native, we are rounding all the pixels automatically.</p>
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<p>We have to be careful when to do this rounding. You never want to work with rounded and unrounded values at the same time as you're going to accumulate rounding errors. Having even one rounding error is deadly because a one pixel border may vanish or be twice as big.</p>
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<p>In React Native, everything in JavaScript and within the layout engine works with arbitrary precision numbers. It's only when we set the position and dimensions of the native element on the main thread that we round. Also, rounding is done relative to the root rather than the parent, again to avoid accumulating rounding errors.</p>
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<h2><a class="anchor" aria-hidden="true" id="example"></a><a href="#example" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Example</h2>
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<div class="snack-player"><div class="mobile-friendly-snack" style="display: none"><pre><code class="hljs css javascript"><span class="hljs-keyword">import</span> React <span class="hljs-keyword">from</span> <span class="hljs-string">"react"</span>;
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<span class="hljs-keyword">import</span> { Image, PixelRatio, ScrollView, StyleSheet, Text, TextInput, View } <span class="hljs-keyword">from</span> <span class="hljs-string">"react-native"</span>;
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<span class="hljs-keyword">const</span> size = <span class="hljs-number">50</span>;
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<span class="hljs-keyword">const</span> cat = {
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<span class="hljs-attr">uri</span>: <span class="hljs-string">"https://reactnative.dev/docs/assets/p_cat1.png"</span>,
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<span class="hljs-attr">width</span>: size,
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<span class="hljs-attr">height</span>: size
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};
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<span class="hljs-keyword">export</span> <span class="hljs-keyword">default</span> App = <span class="hljs-function"><span class="hljs-params">()</span> =></span> (
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<ScrollView style={styles.scrollContainer}>
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<View style={styles.container}>
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<Text>Current Pixel Ratio is:</Text>
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<Text style={styles.value}>{PixelRatio.get()}</Text>
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</View>
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<View style={styles.container}>
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<Text>Current Font Scale is:</Text>
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<Text style={styles.value}>{PixelRatio.getFontScale()}</Text>
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</View>
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<View style={styles.container}>
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<Text>On this device images with a layout width of</Text>
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<Text style={styles.value}>{size} px</Text>
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<Image source={cat} />
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</View>
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<View style={styles.container}>
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<Text>require images with a pixel width of</Text>
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<Text style={styles.value}>
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{PixelRatio.getPixelSizeForLayoutSize(size)} px
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</Text>
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<Image
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source={cat}
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style={{
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width: PixelRatio.getPixelSizeForLayoutSize(size),
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height: PixelRatio.getPixelSizeForLayoutSize(size)
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}}
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/>
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</View>
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</ScrollView>
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);
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const styles = StyleSheet.create({
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scrollContainer: {
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flext: 1,
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marginTop: "2em",
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justifyContent: "center",
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},
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container: {
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justifyContent: "center",
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alignItems: "center"
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},
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value: {
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fontSize: 24,
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marginBottom: 12,
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marginTop: 4
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}
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});
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</code></pre></div><div class="desktop-friendly-snack" style="margin-top: 15px; margin-bottom: 15px"><div
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data-snack-name="PixelRatio Example"
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data-snack-description="Example usage"
|
||
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"
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></div></div></div><hr>
|
||
<h1><a class="anchor" aria-hidden="true" id="reference"></a><a href="#reference" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Reference</h1>
|
||
<h2><a class="anchor" aria-hidden="true" id="methods"></a><a href="#methods" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Methods</h2>
|
||
<h3><a class="anchor" aria-hidden="true" id="get"></a><a href="#get" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a><code>get()</code></h3>
|
||
<pre><code class="hljs css language-jsx"><span class="token keyword">static</span> <span class="token keyword">get</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
</code></pre>
|
||
<p>Returns the device pixel density. Some examples:</p>
|
||
<ul>
|
||
<li><code>PixelRatio.get() === 1</code>
|
||
<ul>
|
||
<li><a href="https://material.io/tools/devices/">mdpi Android devices</a></li>
|
||
</ul></li>
|
||
<li><code>PixelRatio.get() === 1.5</code>
|
||
<ul>
|
||
<li><a href="https://material.io/tools/devices/">hdpi Android devices</a></li>
|
||
</ul></li>
|
||
<li><code>PixelRatio.get() === 2</code>
|
||
<ul>
|
||
<li>iPhone SE, 6S, 7, 8</li>
|
||
<li>iPhone XR</li>
|
||
<li>iPhone 11</li>
|
||
<li><a href="https://material.io/tools/devices/">xhdpi Android devices</a></li>
|
||
</ul></li>
|
||
<li><code>PixelRatio.get() === 3</code>
|
||
<ul>
|
||
<li>iPhone 6S Plus, 7 Plus, 8 Plus</li>
|
||
<li>iPhone X, XS, XS Max</li>
|
||
<li>iPhone 11 Pro, 11 Pro Max</li>
|
||
<li>Pixel, Pixel 2</li>
|
||
<li><a href="https://material.io/tools/devices/">xxhdpi Android devices</a></li>
|
||
</ul></li>
|
||
<li><code>PixelRatio.get() === 3.5</code>
|
||
<ul>
|
||
<li>Nexus 6</li>
|
||
<li>Pixel XL, Pixel 2 XL</li>
|
||
<li><a href="https://material.io/tools/devices/">xxxhdpi Android devices</a></li>
|
||
</ul></li>
|
||
</ul>
|
||
<hr>
|
||
<h3><a class="anchor" aria-hidden="true" id="getfontscale"></a><a href="#getfontscale" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a><code>getFontScale()</code></h3>
|
||
<pre><code class="hljs css language-jsx"><span class="token keyword">static</span> <span class="token function">getFontScale</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">:</span> number
|
||
</code></pre>
|
||
<p>Returns the scaling factor for font sizes. This is the ratio that is used to calculate the absolute font size, so any elements that heavily depend on that should use this to do calculations.</p>
|
||
<ul>
|
||
<li>on Android value reflects the user preference set in <strong>Settings > Display > Font size</strong></li>
|
||
<li>on iOS it will always return the default pixel ratio</li>
|
||
</ul>
|
||
<p>If a font scale is not set, this returns the device pixel ratio.</p>
|
||
<hr>
|
||
<h3><a class="anchor" aria-hidden="true" id="getpixelsizeforlayoutsize"></a><a href="#getpixelsizeforlayoutsize" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a><code>getPixelSizeForLayoutSize()</code></h3>
|
||
<pre><code class="hljs css language-jsx"><span class="token keyword">static</span> <span class="token function">getPixelSizeForLayoutSize</span><span class="token punctuation">(</span>layoutSize<span class="token punctuation">:</span> number<span class="token punctuation">)</span><span class="token punctuation">:</span> number
|
||
</code></pre>
|
||
<p>Converts a layout size (dp) to pixel size (px).</p>
|
||
<p>Guaranteed to return an integer number.</p>
|
||
<hr>
|
||
<h3><a class="anchor" aria-hidden="true" id="roundtonearestpixel"></a><a href="#roundtonearestpixel" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a><code>roundToNearestPixel()</code></h3>
|
||
<pre><code class="hljs css language-jsx"><span class="token keyword">static</span> <span class="token function">roundToNearestPixel</span><span class="token punctuation">(</span>layoutSize<span class="token punctuation">:</span> number<span class="token punctuation">)</span><span class="token punctuation">:</span> number
|
||
</code></pre>
|
||
<p>Rounds a layout size (dp) to the nearest layout size that corresponds to an integer number of pixels. For example, on a device with a PixelRatio of 3, <code>PixelRatio.roundToNearestPixel(8.4) = 8.33</code>, which corresponds to exactly (8.33 * 3) = 25 pixels.</p>
|
||
</span></div></article></div><div class="docs-prevnext"><a class="docs-prev button" href="/docs/panresponder"><span class="arrow-prev">← </span><span class="function-name-prevnext">PanResponder</span></a><a class="docs-next button" href="/docs/share"><span>Share</span><span class="arrow-next"> →</span></a></div></div></div><nav class="onPageNav"><ul class="toc-headings"><li><a href="#fetching-a-correctly-sized-image">Fetching a correctly sized image</a></li><li><a href="#pixel-grid-snapping">Pixel grid snapping</a></li><li><a href="#example">Example</a></li><li><a href="#methods">Methods</a><ul class="toc-headings"><li><a href="#get"><code>get()</code></a></li><li><a href="#getfontscale"><code>getFontScale()</code></a></li><li><a href="#getpixelsizeforlayoutsize"><code>getPixelSizeForLayoutSize()</code></a></li><li><a href="#roundtonearestpixel"><code>roundToNearestPixel()</code></a></li></ul></li></ul></nav></div><footer class="nav-footer" id="footer"><section class="sitemap"><div><h5>Docs</h5><a href="/docs/getting-started.html">Getting Started</a><a href="/docs/tutorial.html">Tutorial</a><a href="/docs/components-and-apis.html">Components and APIs</a><a href="/docs/more-resources.html">More Resources</a></div><div><h5>Community</h5><a href="/help.html">The React Native Community</a><a href="/showcase.html">Who's using React Native?</a><a href="http://stackoverflow.com/questions/tagged/react-native" target="_blank">Ask Questions on Stack Overflow</a><a href="https://github.com/facebook/react-native/blob/master/CONTRIBUTING.md">Contributor Guide</a><a href="https://dev.to/t/reactnative" target="_blank">DEV Community</a></div><div><h5>More Resources</h5><a href="/blog/">Blog</a><a href="https://twitter.com/reactnative" target="_blank">Twitter</a><a href="https://github.com/facebook/react-native" target="_blank">GitHub</a><a href="https://reactjs.org" target="_blank">React</a></div></section><a href="https://code.facebook.com/projects/" target="_blank" class="fbOpenSource"><img src="/img/oss_logo.png" alt="Facebook Open Source" width="170" height="45"/></a><section class="copyright">Copyright © 2020 Facebook Inc.</section></footer></div><script type="text/javascript" src="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.js"></script><script>window.fbAsyncInit = function() {FB.init({appId:'1677033832619985',xfbml:true,version:'v2.7'});};(function(d, s, id){var js, fjs = d.getElementsByTagName(s)[0];if (d.getElementById(id)) {return;}js = d.createElement(s); js.id = id;js.src = '//connect.facebook.net/en_US/sdk.js';fjs.parentNode.insertBefore(js, fjs);}(document, 'script','facebook-jssdk'));
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