VideoOverlay

Programmer's Reference Manuals

» List of modules

» VideoOverlay

The VideoOverlay module acts as a manager for any graphics/video overlays that are supported by the system, e.g. for directly displaying YUV video frames. Its SWIs act as a high-level interface which applications can use to create and manipulate overlays.

Internally, it uses the GraphicsV API to manage the overlays (e.g. reason codes 20-28). The GraphicsV overlay API is a low-level interface that should not be used directly by programs, as any overlay operations which are performed via GraphicsV may conflict with operations that VideoOverlay (or a replacement manager module) may be performing.

The current version of the module is functional, but incomplete. Once completed, its full set of duties are expected to include:

• Rendering (or coordinating the rendering) of alpha/TCK sections to allow Z-order overlays to be visible
• Associating overlays with Wimp windows/tasks
  • Allows Z-order to be automatically updated
  • Ensures overlay is destroyed if task exits or window is destroyed
• Notifying programs of when their overlays have been lost
• The public API doesn’t use GraphicsV overlay IDs directly; instead a different ID system is used, to prevent a program which has lost its overlay due to a mode change from accidentally interacting with an overlay that belongs to a different program
• Dealing with some of the complexities of the “Basic” overlay type
• Software emulation of overlays
• Allowing screen output to be redirected to an overlay

With the overlay ID system that VideoOverlay uses, zero is a suitable value for programs to use as an invalid overlay ID.

Since generic hardware overlays aren’t a critical system component, the VideoOverlay module is typically disc-based rather than ROM-based. Thus, programs which expect to use it should attempt to RMLoad it from !System, in the usual manner.

Details

• SWI Calls

See also

• GraphicsV