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问题:

I'm designing an HTML page for display in Android browsers. Consider this simple example page:

<html>
<head><title>Simple!</title>
</head>
<body>
<p><img src="http://sstatic.net/so/img/logo.png"></p>
</body>
</html>

It looks just fine on the standard HVGA phones (320x480), but on HDPI WVGA sizes (480x800 or 480x854) the built-in browser automatically scales the image up; it looks ugly.

I've read that I should be able to use this tag to force the browser to stop scaling my page:

<meta name="viewport" content="width=device-width; initial-scale=1.0; maximum-scale=1.0; minimum-scale=1.0; user-scalable=0;" />

... but all that does is disable user scaling (the zoom buttons disappear); it doesn't actually prevent the browser from scaling my image. Adjusting the scale factors (setting them all to 2.0 or 0.5) has no effect at all.

How can I force the WVGA browser to stop scaling my images?

回答1:

Ah, found it by searching through the Android source code. There's a new Android-specific "target-densityDpi" setting available in the "viewport" meta tag; as far as I can tell, it's totally undocumented, except for the check-in comment!

Add dpi support for WebView.

In the "viewport" meta tag, you can specify "target-densityDpi". If it is not specified, it uses the default, 160dpi as of today. Then the 1.0 scale factor specified in the viewport tag means 100% on G1 and 150% on Sholes. If you set "target-densityDpi" to "device-dpi", then the 1.0 scale factor means 100% on both G1 and Sholes.

Implemented Safari's window.devicePixelRatio and css media query device-pixel-ratio.

So if you use "device-dpi" and modify the css for font-size and image src depending on window.devicePixelRatio, you can get a better page on Sholes/Passion.

Here is a list of options for "target-densityDpi".

device-dpi: Use the device's native dpi as target dpi. low-dpi: 120dpi medium-dpi: 160dpi, which is also the default as of today high-dpi: 240dpi : We take any number between 70 and 400 as a valid target dpi.