widget/material: split Decorations state and style

Move Decorations to the widget package and
rename material.Decorate to material.Decorations.
This makes decorations in line with how the
other widgets are used.

Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

widget/decorations.go

@@ -0,0 +1,127 @@
+package widget
+
+import (
+	"fmt"
+	"image"
+	"math/bits"
+
+	"gioui.org/gesture"
+	"gioui.org/io/pointer"
+	"gioui.org/io/system"
+	"gioui.org/layout"
+	"gioui.org/op/clip"
+	"gioui.org/unit"
+)
+
+// Decorations handles the states of window decorations.
+type Decorations struct {
+	move   gesture.Drag
+	clicks []Clickable
+	resize [8]struct {
+		gesture.Hover
+		gesture.Drag
+	}
+	actions   system.Action
+	maximized bool
+}
+
+// LayoutMove lays out the widget that makes a window movable.
+func (d *Decorations) LayoutMove(gtx layout.Context, w layout.Widget) layout.Dimensions {
+	dims := w(gtx)
+	d.move.Events(gtx.Metric, gtx, gesture.Both)
+	st := clip.Rect{Max: dims.Size}.Push(gtx.Ops)
+	d.move.Add(gtx.Ops)
+	if d.move.Pressed() {
+		d.actions |= system.ActionMove
+	}
+	st.Pop()
+	return dims
+}
+
+// Clickable returns the clickable for the given single action.
+func (d *Decorations) Clickable(action system.Action) *Clickable {
+	if bits.OnesCount(uint(action)) != 1 {
+		panic(fmt.Errorf("not a single action"))
+	}
+	idx := bits.TrailingZeros(uint(action))
+	if n := idx - len(d.clicks); n >= 0 {
+		d.clicks = append(d.clicks, make([]Clickable, n+1)...)
+	}
+	click := &d.clicks[idx]
+	if click.Clicked() {
+		if action == system.ActionMaximize {
+			if d.maximized {
+				d.maximized = false
+				d.actions |= system.ActionUnmaximize
+			} else {
+				d.maximized = true
+				d.actions |= system.ActionMaximize
+			}
+		} else {
+			d.actions |= action
+		}
+	}
+	return click
+}
+
+// LayoutResize lays out the resize actions.
+func (d *Decorations) LayoutResize(gtx layout.Context, actions system.Action) {
+	cs := gtx.Constraints.Max
+	wh := gtx.Px(unit.Dp(10))
+	s := []struct {
+		system.Action
+		image.Rectangle
+	}{
+		{system.ActionResizeNorth, image.Rect(0, 0, cs.X, wh)},
+		{system.ActionResizeSouth, image.Rect(0, cs.Y-wh, cs.X, cs.Y)},
+		{system.ActionResizeWest, image.Rect(cs.X-wh, 0, cs.X, cs.Y)},
+		{system.ActionResizeEast, image.Rect(0, 0, wh, cs.Y)},
+		{system.ActionResizeNorthWest, image.Rect(0, 0, wh, wh)},
+		{system.ActionResizeNorthEast, image.Rect(cs.X-wh, 0, cs.X, wh)},
+		{system.ActionResizeSouthWest, image.Rect(0, cs.Y-wh, wh, cs.Y)},
+		{system.ActionResizeSouthEast, image.Rect(cs.X-wh, cs.Y-wh, cs.X, cs.Y)},
+	}
+	for i, data := range s {
+		action := data.Action
+		if actions&action == 0 {
+			continue
+		}
+		rsz := &d.resize[i]
+		rsz.Events(gtx.Metric, gtx, gesture.Both)
+		if rsz.Drag.Dragging() {
+			d.actions |= action
+		}
+		st := clip.Rect(data.Rectangle).Push(gtx.Ops)
+		if rsz.Hover.Hovered(gtx) {
+			pointer.CursorNameOp{Name: action.CursorName()}.Add(gtx.Ops)
+		}
+		rsz.Drag.Add(gtx.Ops)
+		pass := pointer.PassOp{}.Push(gtx.Ops)
+		rsz.Hover.Add(gtx.Ops)
+		pass.Pop()
+		st.Pop()
+	}
+}
+
+// Perform updates the decorations as if the specified actions were
+// performed by the user.
+func (d *Decorations) Perform(actions system.Action) {
+	if actions&system.ActionMaximize != 0 {
+		d.maximized = true
+	}
+	if actions&(system.ActionUnmaximize|system.ActionMinimize|system.ActionFullscreen) != 0 {
+		d.maximized = false
+	}
+}
+
+// Actions returns the set of actions activated by the user.
+func (d *Decorations) Actions() system.Action {
+	a := d.actions
+	d.actions = 0
+	return a
+}
+
+// Maximized returns whether the window is maximized.
+func (d *Decorations) Maximized() bool {
+	return d.maximized
+}