# Retail favorite spell-bar overflow pseudocode

This note is the implementation oracle for world-interaction completion Slice
1. Addresses refer to the September 2013 EoR named retail client. The exact
element graph and inherited properties were verified against combat LayoutDesc
`0x21000073` and the existing imported fixture
`combat_21000073.json`.

## Authored element graph

Each of the eight `SpellCastSubMenu` groups contains:

```text
favorite group
  scrollbar 0x100000B5, 685x36
    decrement button 0x10000071, 23x36
      Normal   0x06004CDC
      Rollover 0x06004CDD
    increment button 0x10000072, 23x36
      Normal   0x06004CDE
      Rollover 0x06004CDF
  item list 0x100000B6, x=23, y=2, 639x32

scrollbar property 0x77 = increment button 0x10000072
scrollbar property 0x78 = decrement button 0x10000071
scrollbar property 0x79 = HideDisabled true
item-list property 0x71 = horizontal scrollbar 0x100000B5
```

The spell-bar scrollbar has no authored track or thumb. Its 23-pixel buttons
occupy the space immediately outside the 639-pixel item-list viewport.

## Initialization and ownership

Retail:

- `SpellCastSubMenu::Init @ 0x004C5A90`
- `UIElement_Scrollable::PostInit @ 0x004744B0`
- `UIElement_Scrollable::OnSetAttribute @ 0x00474630`

```text
SpellCastSubMenu.Init(parent, groupId, tabId, tabIndex):
    group = parent.GetChildRecursive(groupId)
    spellItemList = group.GetChildRecursive(0x100000B6)
    register this as the item-list drag handler
    spellTabElement = parent.GetChildRecursive(tabId)

UIElement_Scrollable.OnSetAttribute(property):
    if property id == 0x71:
        horizontalScrollbarId = property element id

UIElement_Scrollable.PostInit():
    horizontalScrollbar = resolve horizontalScrollbarId
    register for scrollbar messages
    UpdateScrollbarSize(horizontal=true)
```

The controller does not synthesize arrow buttons. LayoutDesc owns them; the
ordinary scrollable/listbox relationship owns the offset.

## Size, disabled state, and visibility

Retail:

- `UIElement_Scrollable::UpdateScrollbarSize_ @ 0x004741A0`
- `UIElement_Scrollbar::SetDisabled @ 0x004703D0`
- `UIElement_Scrollbar::SetHideDisabled @ 0x00470400`
- `UIElement_Scrollbar::UpdateLayout @ 0x004710D0`

```text
UpdateScrollbarSize(horizontal):
    content = scrollableWidth
    viewport = element.Width

    if content <= viewport:
        content = viewport
        scrollOffsetX = 0
        disabled = true
    else:
        disabled = false

    scrollbar.Horizontal = true
    scrollbar.Disabled = disabled
    scrollbar.Proportion = min(1, viewport / content)

Scrollbar.UpdateLayout():
    scrollingArea = own rectangle
    position decrement button at the start and subtract its authored width
    position increment button at the end and subtract its authored width
    update thumb/track geometry, when those children exist
    Visible = NOT (Disabled AND HideDisabled)
```

For the favorite bar, disabled plus HideDisabled removes both arrows when every
favorite/empty cell fits. With overflow, the arrows remain visible and the
item list clips the horizontally translated cells.

## Scroll delta and selection exposure

Retail:

- `UIElement_Scrollable::HandleScrollbarMessage_ @ 0x00474370`
- `UIElement_ListBox::InqScrollDelta @ 0x0046DC10`
- `SpellCastSubMenu::SetSelected @ 0x004C5B00`

```text
on decrement:
    delta = -itemList.InqScrollDelta(horizontal, line)
    set horizontal pixel offset += delta

on increment:
    delta = +itemList.InqScrollDelta(horizontal, line)
    set horizontal pixel offset += delta

ItemList.InqScrollDelta(horizontal, line):
    if column count is nonzero:
        return min(viewportWidth, scrollableWidth / columnCount)
    return 0

SpellCastSubMenu.SetSelected(spellId):
    for each item in list order:
        item.Selected = item.spellId == spellId
        if selected:
            endowmentSelected = false
            itemList.ScrollToView(itemIndex)
    selectedSpellId = spellId
```

The favorite cells are 32 pixels wide, so a line arrow moves exactly 32
pixels. Programmatic or keyboard selection exposes the selected cell even when
it was outside the prior viewport.

## Port constraints

- Preserve the imported `0x71`/`0x77`/`0x78` relationships.
- Preserve each authored button's dimension; do not assume the 16-pixel chat
  scrollbar button size.
- Do not fabricate a track/thumb for this arrow-only control.
- Derive disabled state from the shared model's content and viewport extents.
- Hide disabled controls from both drawing and hit-testing.
- Keep every favorite tab's scroll offset independent.