Introduction
The DragASprite module provides SWI calls with which you can make the pointer drag a sprite around the screen. Since not all users will prefer this effect to dragging an outline - whether for aesthetics or performance - there is a bit in the CMOS RAM used to indicate their preference. (See the chapter entitled Non-volatile memory (CMOS RAM).) You should examine that bit before using this module; if it shows that the user would prefer to drag outlines, oblige them!
To drag a sprite:
- Prepare a sprite to be dragged (this may be trivial, as the application may have a suitable sprite already to hand).
- Call the SWI SWI DragASprite_Start. This takes a copy of your sprite - so you can dispose of your copy whenever you like - and then starts a Wimp drag.
- When the Wimp sends you an indication that your drag has finished, you should call the SWI SWI DragASprite_Stop to release the workspace used for the drag.
SWI calls
| R0 | = | flags :
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| R1 | = | sprite area holding sprite:
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| R2 | = | pointer to sprite name | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| R3 | = | pointer to 16-byte block containing box | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| R4 | = | pointer to optional 16-byte block containing bounding box (see flags) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| R0 - R4 | preserved | |
This call starts dragging a sprite. The sprite you supply is copied, so there is no problem if you dispose of your copy of the sprite. If there is insufficient memory available to start the drag, the call reverts to a normal drag of a dotted outline.
The blocks pointed to by R3 and - optionally - R4 have the following format:
| Offset | Name | Use |
|---|---|---|
| 0 | x-low | |
| 4 | y-low | bottom-left (x-low, y-low) is inclusive |
| 8 | x-high | top-right (x-high, y-high) is exclusive |
| 12 | y-high |
This call terminates any current drag operation, and releases any workspace claimed by the DragASprite module to do a drag. You should make this call when your application receives the User_Drag_Box reason code from SWI Wimp_Poll during a drag.