Transparency
Functional Description
Qt 4 supports transparency between widgets. Qtopia uses this to allow a background image to be seen behind the user interface controls.
Features
Theme Background Specification
The background is specified by the background element in the homescreen theme definition.
Background Selection
Themes should allow the background displayed to be selected by the user by including the background plug-in as part of the background element, for example:
<group name="background">
<image name="background" rect="0,0,0,0" src="background" color="Highlight" tile="yes"/>
<plugin name="bgplugin"/>
</group>
This allows the background to be specified by the Appearance settings application. If no background is specified by the user then the background is specified entirely by the theme. Since the theme elements are rendered in order specified in the theme, it is possible to add watermarks over the user's selected background to maintain branding.
Background Tinting
When the background is displayed outside the homescreen it is tinted with the window color to ensure all text is visible regardless of how dark the background is.
Transparent Colors
Most standard palette colors which are typically used as brushes are assigned some transparency so that the background is visible even when the programmer paints over it. This does place some responsibility with the developer when painting to ensure that the correct effect is achieved. In particular it is important not to "overdraw" some areas, since the overlapping region will appear darker than desired and the background will be less visible.
Shadow Effect
Pop-up windows, for example menus and comboboxes, are displayed with a transparent shadow to provide the illusion of depth.
