Device adaptation

Artikel
11/03/2017

As a web (or Windows app using JavaScript) developer, you are faced with a dilemma: Code your site to work with as many devices, sizes, and resolutions as possible; or risk alienating users by potentially allowing your content to be either clipped (in fixed layouts) or jumbled confusingly (in fluid layouts). The @-ms-viewport rule, in combination with Cascading Style Sheets (CSS) Media Queries, attempts to solve this dilemma by enabling web developers and developers of Windows apps using JavaScript for Windows 8 to optimize the layout of sites and apps for different devices with minimal effort.

The @-ms-viewport rule is based on the @viewport rule, which is defined in the CSS Device Adaptation specification. This specification is currently in the Working Draft stage. Be aware that the implementation of @-ms-viewport in Internet Explorer 10 and Windows apps using JavaScript does not map exactly to the information defined in the specification. This might change as the CSS Device Adaptation specification is revised and improved.

Viewing sites in narrow windows

Most sites on the web today are not very usable when viewed in a very narrow window. Fixed layouts can become clipped, and fluid layouts can become jumbled. App scenarios in Windows 8 often involve very narrow windows. To avoid problems with clipping or jumbling of content, content is automatically scaled down. This requires no extra effort from you as a developer, but it might not be ideal, depending on the default width of your content. Users will be forced to zoom every time they need to access the content.

By using the @-ms-viewport rule, can more easily deliver optimized sites and apps. Instead of forcing you into a "one-size-fits-all" scenario where you might have to awkwardly enlarge a small UI or over-compress a large UI, you can use both @-ms-viewport and existing support for CSS Media Queries to optimize your site or app for different ranges of resolutions. You can specify that pages that are optimized for a particular range are scaled more naturally for devices with resolutions within that range. This enables you to optimize your site not just for desktop displays, but for small slates, or even for the snapped state.

Using the @-ms-viewport rule

The @-ms-viewport rule works in tandem with media queries to help optimize your layout. Typically, you nest the @-ms-viewport rule inside the media query, as shown in the following pseudocode snippet:

@media [media query logic here] {
  @-ms-viewport {
    [viewport size here]
  }
  [CSS for this layout combination goes here.]
}

Be aware that, in browsers other than Internet Explorer 10 (or in older versions of Windows Internet Explorer), this CSS degrades gracefully. The @-ms-viewport rule and its contents, if not recognized, are simply ignored.

Example usage: Web page with snapped state optimization

The following example shows a common use for the @-ms-viewport rule. Specifically, this selector can be used to optimize a small version of your webpage for viewing in the snapped state.

@media screen and (max-width: 400px) {
  @-ms-viewport { width: 320px; }
  /* CSS for 320px width Modern taskbar layout goes here */
}

Any viewport smaller than 400 pixels in width (for instance, the snapped state), is laid out to a width of 320 pixels and scaled to fit. The CSS listed underneath it (which has presumably been optimized for a small screen) will be applied.

Example usage: Fixed-size application

Following is a very basic example of the @-ms-viewport rule in use, without any media query (indicating the rule applies in all cases).

@-ms-viewport {
  width: 1024px;
  height: 768px;
}

This example might be used, for instance, in a Windows app using JavaScript that is locked to landscape mode. It specifies that, regardless of the resolution of the display or the display ratio (4:3, 16:9 widescreen, and so on), the displayed content (the "viewport") must always contain at minimum 1024 pixels by 768 pixels. In the case of a display that is, for instance, 1920 pixels by 1080 pixels (16:9 widescreen ratio), the viewport is scaled up to fit the display's height. Because it is a widescreen display, the application can be centered using normal CSS methods for a "pillarboxing" effect (black bars on both sides of the viewport). On a 1280×960 display, because its aspect ratio is equal to that of the 1024×768 viewport, the viewport would scale up to fill the display completely.

We can expand this example by adding media queries that allow for both landscape and portrait modes in this app:

@media screen and (orientation: landscape) {
  @-ms-viewport {
    width: 1024px;
    height: 768px;
  }
  /* CSS for landscape layout goes here */
}

@media screen and (orientation: portrait) {
  @-ms-viewport {
    width: 768px;
    height: 1024px;
  }
  /* CSS for portrait layout goes here */
}

This example does effectively the same thing as the previous example, except that the portrait orientation is accounted for in the second @media rule. In the case of portrait mode, the orientation of the content might change (text and pictures might be laid out differently to account for the difference in direction), but the viewport stays the same. The width and height values have been swapped, so the visible content area does not change.

Example usage: Optimizing for width

Following is an example of a page whose scaling behavior has been optimized for width using media queries and @-ms-viewport. Notice that each media query covers a different resolution range. Within each range, the @-ms-viewport rule specifies what width any device that falls within that range should scale to. The CSS that follows each rule then defines exactly how to display the content that has been scaled for that resolution range.

@media screen and (max-width: 400px) {
    @-ms-viewport { width: 320px; }
    /* CSS for 320px layout goes here */
}

@media screen and (min-width: 400px) and (max-width: 640px) {
    @-ms-viewport { width: 400px; }
    /* CSS for 400px layout goes here */
}

@media screen and (min-width: 640px) and (max-width: 1024px) {
    @-ms-viewport { width: 640px; }
    /* CSS for 640px layout goes here */
}

@media screen and (min-width: 1024px) and (max-width: 1366px) {
    @-ms-viewport { width: 1024px; }
    /* CSS for 1024px layout goes here */
}

@media screen and (min-width: 1366px) {
    /* CSS for 1366px layout goes here */
}

Example usage: Opting out of automatic scaling

By default, the Internet Explorer in the new Windows UI in the new Windows UI automatically scales content when the window is narrower than 1024 pixels. This primarily includes the snapped state and portrait mode.

However, in cases where this automatic scaling is not needed or desired, the device-width keyword can be used. This keyword signifies that the page is optimized to work well regardless of the width of the device.