App rendering differences on Chromebooks

Because Android apps run in a window under ChromeOS, there are small differences in how apps are rendered on Chromebooks. These differences are outlined in the following paragraphs.

Tasks, windows, and transparency

A task consists of a stack of activities that the user interacts with when running an app. Tasks are presented on ChromeOS as a window with a title bar, with the apps layered on top of each other. Each activity can then be partially translucent, letting the lower layers show through.

In a conventional Android app, the previous task or the desktop shows through beneath the task. In this way, there is always something visible beneath a translucent task.

This does not work in a window environment, for the following reasons:

• The visible content below a window cannot be controlled, and could therefore be anything.
• Fully transparent pixels could "magically" swallow touch or mouse events.
• Window elements might visually be disconnected from the caption, confusing the user with possibly unconnected visual elements.

To mitigate this problem, Play for ChromeOS draws a semitransparent rectangle behind each window. For this reason, apps can never be 100 percent transparent when running under ChromeOS, even when using the Theme.Translucent.NoTitleBar theme.