feat(markup): a list column can draw a button in each row

docs/plugin-ui-markup.md

@@ -313,13 +313,14 @@ The two forms cannot be mixed on one list.
       selected="{SelectedMonster}" onchange="{SelectMonster}">
   <column type="check" width="20"  values="{MonsterFlags}" onchange="{ToggleFlag}"/>
   <column type="text"  width="127" items="{MonsterNames}"  onclick="{PingMonster}"/>
-  <column type="icon"  width="*"   iconkind="did" values="{MonsterIcons}" onclick="{MoveUp}"/>
+  <column type="icon"  width="20"  iconkind="did" values="{MonsterIcons}" onclick="{MoveUp}"/>
+  <column type="button" width="*"  items="{MonsterActions}" onclick="{ActOnMonster}"/>
 </list>
 ```
 
 | Attribute | Column type | Required | Binding |
 |---|---|---|---|
-| `type` | all | yes | `text`, `check`, or `icon` |
+| `type` | all | yes | `text`, `check`, `icon`, or `button` |
 | `width` | all | see below | pixels, or `*` for auto |
 | `items` | `text` | yes | `IReadOnlyList<string>` |
 | `colors` | `text` | no | `IReadOnlyList<uint>` or `<int>`, `0xRRGGBB` per row |
@@ -329,19 +330,44 @@ The two forms cannot be mixed on one list.
 | `values` | `icon` | yes | `IReadOnlyList<uint>` or `<int>` |
 | `iconkind` | `icon` | no | `did` (default), `spell`, or `item` |
 | `onclick` | `icon` | yes | `Action<int>` with the row index |
+| `items` | `button` | yes | `IReadOnlyList<string>`, each row's caption; an empty caption draws no button |
+| `onclick` | `button` | yes | `Action<int>` with the row index; the click does not select the row |
+| `buttonw`, `buttonh` | `button` | no | pixels; the button's size, centred in its cell (default: the whole cell) |
 
 Widths: `*` shares the remaining width equally with every other `*` column.
 The last column is always automatic; it takes the whole remainder unless
 another column is also `*`. Every other column needs a positive `width` or
 `*`. Columns that would overflow the list are clamped and later ones draw
 nothing. Remainder pixels go to the last sharing column.
 
-Rows: the row count is the longest bound column. A `text` or `icon` cell past
-its own column's data draws nothing; a `check` cell draws unchecked. A click
+Rows: the row count is the longest bound column. A `text`, `icon` or `button`
+cell past its own column's data draws nothing; a `check` cell draws unchecked. A click
 in a `text` column without `onclick` selects the row and fires the list's
 `onchange`; any other click fires the column's own callback and leaves the
 selection alone. A click past a column's own data does nothing.
 
+A `button` cell is drawn as a button one pixel inside its cell, or at
+`buttonw` by `buttonh` centred in the cell (never larger than the cell; set
+either alone to size only that side), with its caption centred in the list's
+text colour and cut off at the button's edges. Without a theme its face and
+border are those of an unthemed `<button>`. On a themed window the face is the
+theme's background colour (the list itself is drawn in the field colour that
+a themed `<button>` uses) and the border is the theme's border colour. Unlike
+a `<button>`, it lightens while hovered and darkens while pressed. A disabled
+list draws its buttons' face, border and caption faded and fires none of them.
+
+It fires like a `<button>`, when the left button comes up over the button it
+went down on, so a press dragged off the button cancels it; a click beside a
+smaller button does nothing. Because `onclick` gets a row index, a press is
+also cancelled if, before the release, the list scrolls, its row count changes,
+or the pressed button's own caption changes or becomes empty. Changes in the
+row's other columns, such as a distance that updates every frame, do not
+cancel it, so a plugin that reorders rows with the same count should change
+the caption too, or the click fires for whatever item is at the pressed row.
+A cell with an empty caption is not a button and ignores clicks.
+On a host older than button columns, a `type="button"` column fails the build
+of its window as an unknown type.
+
 There is no header row; place `<label>` elements above the list. A `check`
 cell draws the same lamp glyph as `<toggle>`. When rows overflow the list's
 height it reserves a 16-pixel scrollbar at its right edge, drawn with the

src/AcDream.App/UI/MarkupDocument.cs

@@ -1009,12 +1009,29 @@ private static UiMarkupListColumn BuildListColumn(
                     : null;
                 return UiMarkupListColumn.Icon(width, valuesSource, resolve, onClick, isAutoWidth);
             }
+            case "button":
+            {
+                var captionSource = BindStringList(
+                    (string?)columnEl.Attribute("items"), binding, ColumnContext(index, "button", "items"));
+                var onClick = BindRequiredIntAction(
+                    (string?)columnEl.Attribute("onclick"), binding, ColumnContext(index, "button", "onclick"));
+                return UiMarkupListColumn.Button(width, captionSource, onClick, isAutoWidth,
+                    ButtonSize(columnEl, "buttonw", index), ButtonSize(columnEl, "buttonh", index));
+            }
             default:
                 throw new FormatException(
-                    $"column[{index}] has unknown type=\"{type}\" (expected text, check, or icon)");
+                    $"column[{index}] has unknown type=\"{type}\" (expected text, check, icon, or button)");
         }
     }
 
+    private static float ButtonSize(XElement columnEl, string attribute, int index)
+    {
+        float size = FOr(columnEl, attribute, 0f);
+        if (size < 0f)
+            throw new FormatException($"{ColumnContext(index, "button", attribute)} must not be negative");
+        return size;
+    }
+
     private static string ColumnContext(int index, string type, string attribute) =>
         $"column[{index}] type=\"{type}\" {attribute}";
 

src/AcDream.App/UI/PluginMarkupTheme.cs

@@ -91,10 +91,13 @@ void Bind(Func<UiDatFont?> get, Action<UiDatFont?> set)
             case UiMarkupList list:
                 var lb = list.BackgroundColor; var le = list.BorderColor; var lt = list.TextColor;
                 var ls = list.SelectedColor; var band = list.SelectionBandEnabled;
+                var lbf = list.ButtonColor; var lbe = list.ButtonBorderColor;
                 panel.AddThemeAction(p => {
                     list.ThemePalette = p; list.BackgroundColor = p?.Field ?? lb;
                     list.BorderColor = p?.Border ?? le; list.TextColor = p?.Text ?? lt;
                     list.SelectedColor = p?.Selected ?? ls; list.SelectionBandEnabled = p is not null || band;
+                    // The list's own ground is the field colour, so its buttons take the window's.
+                    list.ButtonColor = p?.Background ?? lbf; list.ButtonBorderColor = p?.Border ?? lbe;
                 });
                 break;
             case UiScrollbar scroll:

src/AcDream.App/UI/UiControlState.cs

@@ -0,0 +1,4 @@
+namespace AcDream.App.UI;
+
+/// <summary>The look a control takes from the pointer and its own enabled flag.</summary>
+internal enum UiControlState { Normal, Hovered, Pressed, Disabled }