feat(tracker): implement draggable list and make unit list use such

tracker/draglist.go

@@ -0,0 +1,157 @@
+package tracker
+
+import (
+	"image"
+	"image/color"
+
+	"gioui.org/io/pointer"
+	"gioui.org/layout"
+	"gioui.org/op"
+	"gioui.org/op/clip"
+	"gioui.org/op/paint"
+	"gioui.org/widget/material"
+)
+
+type DragList struct {
+	SelectedItem int
+	HoverItem    int
+	List         *layout.List
+	drag         bool
+	dragID       pointer.ID
+	tags         []bool
+	swapped      bool
+}
+
+type FilledDragListStyle struct {
+	dragList      *DragList
+	SurfaceColor  color.NRGBA
+	HoverColor    color.NRGBA
+	SelectedColor color.NRGBA
+	Count         int
+	element       func(gtx C, i int) D
+	swap          func(i, j int)
+}
+
+func FilledDragList(th *material.Theme, dragList *DragList, count int, element func(gtx C, i int) D, swap func(i, j int)) FilledDragListStyle {
+	return FilledDragListStyle{
+		dragList:      dragList,
+		element:       element,
+		swap:          swap,
+		Count:         count,
+		SurfaceColor:  dragListSurfaceColor,
+		HoverColor:    dragListHoverColor,
+		SelectedColor: dragListSelectedColor,
+	}
+}
+
+func (s *FilledDragListStyle) Layout(gtx C) D {
+	swap := 0
+
+	paint.FillShape(gtx.Ops, s.SurfaceColor, clip.Rect{Max: image.Pt(gtx.Constraints.Max.X, gtx.Constraints.Max.Y)}.Op())
+	defer op.Save(gtx.Ops).Load()
+
+	if s.dragList.List.Axis == layout.Horizontal {
+		gtx.Constraints.Min.X = gtx.Constraints.Max.X
+	} else {
+		gtx.Constraints.Min.Y = gtx.Constraints.Max.Y
+	}
+
+	listElem := func(gtx C, index int) D {
+		for len(s.dragList.tags) <= index {
+			s.dragList.tags = append(s.dragList.tags, false)
+		}
+		bg := func(gtx C) D {
+			gtx.Constraints = layout.Exact(image.Pt(120, 20))
+			var color color.NRGBA
+			if s.dragList.SelectedItem == index {
+				color = s.SelectedColor
+			} else if s.dragList.HoverItem == index {
+				color = s.HoverColor
+			}
+			paint.FillShape(gtx.Ops, color, clip.Rect{Max: image.Pt(gtx.Constraints.Min.X, gtx.Constraints.Min.Y)}.Op())
+			return D{Size: gtx.Constraints.Min}
+		}
+		inputFg := func(gtx C) D {
+			defer op.Save(gtx.Ops).Load()
+			for _, ev := range gtx.Events(&s.dragList.tags[index]) {
+				e, ok := ev.(pointer.Event)
+				if !ok {
+					continue
+				}
+				switch e.Type {
+				case pointer.Enter:
+					s.dragList.HoverItem = index
+				case pointer.Leave:
+					if s.dragList.HoverItem == index {
+						s.dragList.HoverItem = -1
+					}
+				case pointer.Press:
+					if s.dragList.drag {
+						break
+					}
+					s.dragList.SelectedItem = index
+				}
+			}
+			rect := image.Rect(0, 0, gtx.Constraints.Min.X, gtx.Constraints.Min.Y)
+			pointer.Rect(rect).Add(gtx.Ops)
+			pointer.InputOp{Tag: &s.dragList.tags[index],
+				Types: pointer.Press | pointer.Enter | pointer.Leave,
+			}.Add(gtx.Ops)
+			if index == s.dragList.SelectedItem {
+				for _, ev := range gtx.Events(s.dragList) {
+					e, ok := ev.(pointer.Event)
+					if !ok {
+						continue
+					}
+					switch e.Type {
+					case pointer.Press:
+						s.dragList.dragID = e.PointerID
+					case pointer.Drag:
+						if s.dragList.dragID != e.PointerID {
+							break
+						}
+						if s.dragList.List.Axis == layout.Horizontal {
+							if e.Position.X < 0 {
+								swap = -1
+							}
+							if e.Position.X > float32(gtx.Constraints.Min.X) {
+								swap = 1
+							}
+						} else {
+							if e.Position.Y < 0 {
+								swap = -1
+							}
+							if e.Position.Y > float32(gtx.Constraints.Min.Y) {
+								swap = 1
+							}
+						}
+					case pointer.Release:
+						fallthrough
+					case pointer.Cancel:
+						s.dragList.drag = false
+					}
+				}
+				pointer.InputOp{Tag: s.dragList,
+					Types: pointer.Drag | pointer.Press | pointer.Release,
+					Grab:  s.dragList.drag,
+				}.Add(gtx.Ops)
+			}
+			return layout.Dimensions{Size: gtx.Constraints.Min}
+		}
+		return layout.Stack{Alignment: layout.W}.Layout(gtx,
+			layout.Expanded(bg),
+			layout.Stacked(func(gtx C) D {
+				return s.element(gtx, index)
+			}),
+			layout.Expanded(inputFg))
+	}
+	dims := s.dragList.List.Layout(gtx, s.Count, listElem)
+	if !s.dragList.swapped && swap != 0 && s.dragList.SelectedItem+swap >= 0 && s.dragList.SelectedItem+swap < s.Count {
+		s.swap(s.dragList.SelectedItem, s.dragList.SelectedItem+swap)
+		s.dragList.SelectedItem += swap
+		s.dragList.swapped = true
+	} else {
+		s.dragList.swapped = false
+	}
+	return dims
+}