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GUI Note Scrolling
This describes the main details about scrolling in the R3 GUI.
If you plan on building custom styles that require scrolling, then you will need to understand how scrolling works. Although a lot of work was done to keep the design as simple as possible, there are still several details that you will need to know in order to build scrollable styles.
In general, scrolling is done with:
- Scrollbars - clicking or dragging scroll bars will scroll the content.
- Scroll events - input from special devices, such as scroll wheels.
- Content - moving or changing content that causes scrolling. For example, moving cursor keys within text.
- API - functions that scroll content programmatically.
Any style that provides an ON-SCROLL actor can be scrolled. Several such styles are provided in the standard system for scrolling panels, text, lists, and images. To set-up scrolling for those styles is simple and does not require any special knowledge.
It should be noted that scrolling is an action of the style and is not dependent on the existence of a scrollbar. It is possible to have scrollable content that has no scrollbars. In such cases, other methods of input are available, such as a scroll wheel or arrow buttons.
For most styles the ON-SCROLL actor will change the offset of a content GOB to move it relative to a display or clipping GOB. However, that is only one approach. A style can perform any action for ON-SCROLL. For example, a 3D style may perform a zoom action for an ON-SCROLL action.
Scrollbar - state values: value and delta as percentages.
Scrollbar are state, so get/set-face. Content style uses facet as property, therefore get/set-facet (not state).
Auto attachment. The common case.
Named attachement. For special purposes.
Face initialization sequence for auto scrolling.
Hover scrolling.
Changing content from scrollbar.
Changing scrollbars from content.
The actors:
on-scroll
on-scroll-event (wheel)
on-delta