a2d/desk.acc/API.md

Desk Accessory API

Desk Accessories for DeskTop have general access to the Mouse Graphics Tool Kit MLI, ProDOS MLI, and DeskTop APIs. Special considerations for DAs are documented here.

Desk Accessory Lifecycle

• DAs are loaded/invoked at $800 MAIN
  • Up to $1C00 MAIN is available
  • But AUX $1B00 and on must be preserved.
• Save stack pointer
• Copy DA code from MAIN to AUX (e.g. using AUXMOVE) at same address.
• Transfer control to the AUX copy
  • This allows direct access to MGTK/DeskTop MLI
  • Retaining a copy in MAIN allows easy access to ProDOS MLI
• Turn on ALTZP and LCBANK1
• Create window (OpenWindow)
• Draw everything
• Flush event queue (FlushEvents)
• Run an event Loop (GetEvent, and subsequent processing, per MGTK)
  • Normal event processing per MGTK
  • In addition, following a window drag/resize, DeskTop calls must be made:
    • JUMP_TABLE_REDRAW_ALL
    • DESKTOP_REDRAW_ICONS
  • ...
• Destroy window (CloseWindow)
• Tell DeskTop to redraw desktop icons (DESKTOP_REDRAW_ICONS)
• Switch control back to MAIN (RAMRDOFF/RAMWRTOFF)
• Ensure ALTZP and LCBANK1 are still on
• Restore stack pointer
• rts