a2d/desk.acc/a2d.md

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# A2D API
There are three distinct API classes that need to be used:
* Main A2D API - entry point $4000 AUX, called MLI-style (JSR followed by command type and address of param block)
* DeskTop Jump Table - simple JSR calls starting at $4003 MAIN, no arguments
* DeskTop API - another MLI-style interface starting at $8E00 AUX
## Main A2D API
### Concepts
#### Box
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The _box_ block is reused in several places. It has the following structure:
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```
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.word left pixels from screen left edge
.word top pixels from screen top edge
.addr addr A2D_SCREEN_ADDR ($2000)
.word stride A2D_SCREEN_STRIDE ($80)
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.word hoff pixels scrolled left
.word voff pixels scrolled up
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.word width pixels wide
.word height pixels tall
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```
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Drawing state can be set to a box (A2D_SET_BOX) and then subsequent operations will occur
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within the box: they will be clipped to the bounds and the offset will be taken into account.
For example, if hoffset is 15 and voffset is 5 then a pixel plotted at 40, 40 will appear
at 40 - 15 = 25 pixels from the left edge and 40 - 5 = 35 pixels from the top edge.
#### Pattern
A simple repeating 8x8 _pattern_ is defined by 8 bytes. All bits of each byte are used.
#### Window Parts
Windows have a _client area_ which has the requested dimensions. Above this is an optional
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_title bar_ which in turn has an optional _close box_. Within the client area are an
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optional _resize box_ and optional _scroll bars_.
### Desk Accessory Lifecycle
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* Loaded/invoked at $800 MAIN (have through $1FFF available)
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* Save stack
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* Copy DA code from MAIN to AUX (e.g. using AUXMOVE)
* Transfer control to AUX
* Turn on ALTZP and LCBANK1
* Create window (A2D_CREATE_WINDOW)
* Draw everything
* Call $2B (no idea what this does!)
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* Enter [input loop](#input-loop)
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* ...
* Destroy window (A2D_DESTROY_WINDOW)
* Redraw desktop icons (DESKTOP_REDRAW_ICONS)
* Switch control back to MAIN (RAMRDOFF/RAMWRTOFF)
* Ensure ALTZP and LCBANK1 are on
* Restore stack
* RTS
> NOTE: Movable windows must maintain an _offscreen_flag_. If a window is moved so that the
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> client area is entirely offscreen then various operations should be skipped because
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> the window's box coordinates will not be set correctly.
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#### Input Loop
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* Call A2D_GET_INPUT.
* If a key (A2D_INPUT_KEY), then check modifiers (Open/Closed Apple) and key code, ignore or take action.
* If a click, call A2D_QUERY_TARGET.
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* If target id not the window id, ignore.
* If target element is desktop (A2D_ELEM_DESKTOP) or menu (A2D_ELEM_MENU) then ignore.
* If target element is close box (A2D_ELEM_CLOSE) then initiate [window close](#window-close).
* If target element is title bar (A2D_ELEM_TITLE) then initiate [window drag](#window-drag).
* If target element is resize box (A2D_ELEM_RESIZE) then initiate [window resize](#window-resize).
* Otherwise, it is client area (A2D_ELEM_CLIENT); call A2D_QUERY_CLIENT.
* If client part is a scrollbar (A2D_VSCROLL or A2D_HSCROLL) then initiate a [scroll](#window-scroll).
* Otherwise, handle a client click using custom logic (e.g. hit testing buttons, etc)
#### Window Close
* Call A2D_CLOSE_CLICK, which enters a modal loop to handle the mouse moving out/in the box.
* Result indicates clicked or canceled; if clicked, exit the DA, otherwise ignore.
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#### Window Drag
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* Call A2D_DRAG_WINDOW.
* Call JUMP_TABLE_REDRAW_ALL.
* If _offscreen flag_ was not set, redraw desktop icons (DESKTOP_REDRAW_ICONS).
* Set _offscreen flag_ if window's `top` is greater than or equal to the screen bottom (191), clear otherwise.
* If _offscreen flag_ is not set, redraw window.
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#### Window Resize
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* Call A2D_DRAG_RESIZE.
* Call JUMP_TABLE_REDRAW_ALL.
* Call DESKTOP_REDRAW_ICONS.
* Call A2D_RESIZE_WINDOW if needed to adjust scroll bar settings. (Details TBD).
* Redraw window.
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#### Window Scroll
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### Drawing Operations
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### Commands
## DeskTop Jump Table
Call from MAIN (RAMRDOFF/RAMWRTOFF). Call style:
```
jsr $xxxx
```
> NOTE: Most of these calls have not been identified yet.
#### JUMP_TABLE_REDRAW_ALL ($4015)
Redraws all DeskTop windows. Required after a drag or resize. Follow with DESKTOP_REDRAW_ICONS call.
#### JUMP_TABLE_CLEAR_SEL ($401E)
Deselect all DeskTop icons (volumes/files).
#### JUMP_TABLE_CUR_POINTER ($4039)
Changes mouse cursor to the default pointer. Note that bitmap is in the language card memory so it must be swapped in.
#### JUMP_TABLE_CUR_WATCH ($403C)
Changes mouse cursor to a watch. Note that bitmap is in the language card memory so it must be swapped in.
## DeskTop API
Call from AUX (RAMRDON/RAMWRTON). Call style:
```
jsr $8E00
.byte command
.addr params
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```
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> NOTE: Only a single call has been identified so far.
Commands:
#### DESKTOP_REDRAW_ICONS ($0C)
Parameters: none (pass $0000 as address)
Redraws the icons on the desktop (mounted volumes, trash). This call is required in these cases:
* After destroying a window (A2D_DESTROY_WINDOW)
* After repainting the desktop (JUMP_TABLE_REDRAW_ALL) following a drag (A2D_DRAG_WINDOW)
* After repainting the desktop (JUMP_TABLE_REDRAW_ALL) following a resize (A2D_DRAG_RESIZE/A2D_RESIZE_WINDOW)