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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="API documentation for the Rust `dpi` mod in crate `winit`."><meta name="keywords" content="rust, rustlang, rust-lang, dpi"><title>winit::dpi - Rust</title><link rel="stylesheet" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../dark.css"><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script src="../../storage.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="shortcut icon" href="../../favicon.ico"><style type="text/css">#crate-search{background-image:url("../../down-arrow.svg");}</style></head><body class="rustdoc mod"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../../winit/index.html'><div class='logo-container'><img src='../../rust-logo.png' alt='logo'></div></a><p class='location'>Module dpi</p><div class="sidebar-elems"><div class="block items"><ul><li><a href="#structs">Structs</a></li><li><a href="#functions">Functions</a></li></ul></div><p class='location'><a href='../index.html'>winit</a></p><script>window.sidebarCurrent = {name: 'dpi', ty: 'mod', relpath: '../'};</script><script defer src="../sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><a id="settings-menu" href="../../settings.html"><img src="../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='out-of-band'><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>−</span>]</a></span><a class='srclink' href='../../src/winit/dpi.rs.html#2-331' title='goto source code'>[src]</a></span><span class='in-band'>Module <a href='../index.html'>winit</a>::<wbr><a class="mod" href=''>dpi</a></span></h1><div class='docblock'><p>DPI is important, so read the docs for this module if you don't want to be confused.</p>
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<p>Originally, <code>winit</code> dealt entirely in physical pixels (excluding unintentional inconsistencies), but now all
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window-related functions both produce and consume logical pixels. Monitor-related functions still use physical
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pixels, as do any context-related functions in <code>glutin</code>.</p>
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<p>If you've never heard of these terms before, then you're not alone, and this documentation will explain the
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concepts.</p>
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<p>Modern screens have a defined physical resolution, most commonly 1920x1080. Indepedent of that is the amount of
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space the screen occupies, which is to say, the height and width in millimeters. The relationship between these two
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measurements is the <em>pixel density</em>. Mobile screens require a high pixel density, as they're held close to the
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eyes. Larger displays also require a higher pixel density, hence the growing presence of 1440p and 4K displays.</p>
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<p>So, this presents a problem. Let's say we want to render a square 100px button. It will occupy 100x100 of the
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screen's pixels, which in many cases, seems perfectly fine. However, because this size doesn't account for the
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screen's dimensions or pixel density, the button's size can vary quite a bit. On a 4K display, it would be unusably
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small.</p>
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<p>That's a description of what happens when the button is 100x100 <em>physical</em> pixels. Instead, let's try using 100x100
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<em>logical</em> pixels. To map logical pixels to physical pixels, we simply multiply by the DPI (dots per inch) factor.
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On a "typical" desktop display, the DPI factor will be 1.0, so 100x100 logical pixels equates to 100x100 physical
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pixels. However, a 1440p display may have a DPI factor of 1.25, so the button is rendered as 125x125 physical pixels.
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Ideally, the button now has approximately the same perceived size across varying displays.</p>
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<p>Failure to account for the DPI factor can create a badly degraded user experience. Most notably, it can make users
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feel like they have bad eyesight, which will potentially cause them to think about growing elderly, resulting in
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them entering an existential panic. Once users enter that state, they will no longer be focused on your application.</p>
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<p>There are two ways to get the DPI factor:</p>
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<ul>
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<li>You can track the <a href="../enum.WindowEvent.html#variant.HiDpiFactorChanged"><code>HiDpiFactorChanged</code></a> event of your
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windows. This event is sent any time the DPI factor changes, either because the window moved to another monitor,
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or because the user changed the configuration of their screen.</li>
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<li>You can also retrieve the DPI factor of a monitor by calling
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<a href="../struct.MonitorId.html#method.get_hidpi_factor"><code>MonitorId::get_hidpi_factor</code></a>, or the
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current DPI factor applied to a window by calling
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<a href="../struct.Window.html#method.get_hidpi_factor"><code>Window::get_hidpi_factor</code></a>, which is roughly equivalent
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to <code>window.get_current_monitor().get_hidpi_factor()</code>.</li>
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</ul>
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<p>Depending on the platform, the window's actual DPI factor may only be known after
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the event loop has started and your window has been drawn once. To properly handle these cases,
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the most robust way is to monitor the <a href="../enum.WindowEvent.html#variant.HiDpiFactorChanged"><code>HiDpiFactorChanged</code></a>
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event and dynamically adapt your drawing logic to follow the DPI factor.</p>
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<p>Here's an overview of what sort of DPI factors you can expect, and where they come from:</p>
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<ul>
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<li><strong>Windows:</strong> On Windows 8 and 10, per-monitor scaling is readily configured by users from the display settings.
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While users are free to select any option they want, they're only given a selection of "nice" DPI factors, i.e.
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1.0, 1.25, 1.5... on Windows 7, the DPI factor is global and changing it requires logging out.</li>
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<li><strong>macOS:</strong> The buzzword is "retina displays", which have a DPI factor of 2.0. Otherwise, the DPI factor is 1.0.
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Intermediate DPI factors are never used, thus 1440p displays/etc. aren't properly supported. It's possible for any
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display to use that 2.0 DPI factor, given the use of the command line.</li>
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<li><strong>X11:</strong> On X11, we calcuate the DPI factor based on the millimeter dimensions provided by XRandR. This can
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result in a wide range of possible values, including some interesting ones like 1.0833333333333333. This can be
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overridden using the <code>WINIT_HIDPI_FACTOR</code> environment variable, though that's not recommended.</li>
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<li><strong>Wayland:</strong> On Wayland, DPI factors are set per-screen by the server, and are always integers (most often 1 or 2).</li>
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<li><strong>iOS:</strong> DPI factors are both constant and device-specific on iOS.</li>
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<li><strong>Android:</strong> This feature isn't yet implemented on Android, so the DPI factor will always be returned as 1.0.</li>
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</ul>
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<p>The window's logical size is conserved across DPI changes, resulting in the physical size changing instead. This
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may be surprising on X11, but is quite standard elsewhere. Physical size changes always produce a
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<a href="../enum.WindowEvent.html#variant.Resized"><code>Resized</code></a> event, even on platforms where no resize actually occurs,
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such as macOS and Wayland. As a result, it's not necessary to separately handle
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<a href="../enum.WindowEvent.html#variant.HiDpiFactorChanged"><code>HiDpiFactorChanged</code></a> if you're only listening for size.</p>
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<p>Your GPU has no awareness of the concept of logical pixels, and unless you like wasting pixel density, your
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framebuffer's size should be in physical pixels.</p>
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<p><code>winit</code> will send <a href="../enum.WindowEvent.html#variant.Resized"><code>Resized</code></a> events whenever a window's logical size
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changes, and <a href="../enum.WindowEvent.html#variant.HiDpiFactorChanged"><code>HiDpiFactorChanged</code></a> events
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whenever the DPI factor changes. Receiving either of these events means that the physical size of your window has
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changed, and you should recompute it using the latest values you received for each. If the logical size and the
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DPI factor change simultaneously, <code>winit</code> will send both events together; thus, it's recommended to buffer
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these events and process them at the end of the queue.</p>
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<p>If you never received any <a href="../enum.WindowEvent.html#variant.HiDpiFactorChanged"><code>HiDpiFactorChanged</code></a> events,
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then your window's DPI factor is 1.</p>
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</div><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
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<table><tr class='module-item'><td><a class="struct" href="struct.LogicalPosition.html" title='winit::dpi::LogicalPosition struct'>LogicalPosition</a></td><td class='docblock-short'><p>A position represented in logical pixels.</p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.LogicalSize.html" title='winit::dpi::LogicalSize struct'>LogicalSize</a></td><td class='docblock-short'><p>A size represented in logical pixels.</p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.PhysicalPosition.html" title='winit::dpi::PhysicalPosition struct'>PhysicalPosition</a></td><td class='docblock-short'><p>A position represented in physical pixels.</p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.PhysicalSize.html" title='winit::dpi::PhysicalSize struct'>PhysicalSize</a></td><td class='docblock-short'><p>A size represented in physical pixels.</p>
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</td></tr></table><h2 id='functions' class='section-header'><a href="#functions">Functions</a></h2>
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<table><tr class='module-item'><td><a class="fn" href="fn.validate_hidpi_factor.html" title='winit::dpi::validate_hidpi_factor fn'>validate_hidpi_factor</a></td><td class='docblock-short'><p>Checks that the DPI factor is a normal positive <code>f64</code>.</p>
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</td></tr></table></section><section id="search" class="content hidden"></section><section class="footer"></section><aside id="help" class="hidden"><div><h1 class="hidden">Help</h1><div class="shortcuts"><h2>Keyboard Shortcuts</h2><dl><dt><kbd>?</kbd></dt><dd>Show this help dialog</dd><dt><kbd>S</kbd></dt><dd>Focus the search field</dd><dt><kbd>↑</kbd></dt><dd>Move up in search results</dd><dt><kbd>↓</kbd></dt><dd>Move down in search results</dd><dt><kbd>↹</kbd></dt><dd>Switch tab</dd><dt><kbd>⏎</kbd></dt><dd>Go to active search result</dd><dt><kbd>+</kbd></dt><dd>Expand all sections</dd><dt><kbd>-</kbd></dt><dd>Collapse all sections</dd></dl></div><div class="infos"><h2>Search Tricks</h2><p>Prefix searches with a type followed by a colon (e.g., <code>fn:</code>) to restrict the search to a given type.</p><p>Accepted types are: <code>fn</code>, <code>mod</code>, <code>struct</code>, <code>enum</code>, <code>trait</code>, <code>type</code>, <code>macro</code>, and <code>const</code>.</p><p>Search functions by type signature (e.g., <code>vec -> usize</code> or <code>* -> vec</code>)</p><p>Search multiple things at once by splitting your query with comma (e.g., <code>str,u8</code> or <code>String,struct:Vec,test</code>)</p></div></div></aside><script>window.rootPath = "../../";window.currentCrate = "winit";</script><script src="../../aliases.js"></script><script src="../../main.js"></script><script defer src="../../search-index.js"></script></body></html>
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