Add the Pager Widget

README.md

@@ -133,6 +133,8 @@ most complex.
   * Works the same as CheckButton and RadioButton but draws a separate
     label next to a small check button. Clicking the label will toggle the
     state of the checkbox.
+* [x] **Pager**: a series of numbered buttons to use with a paginated UI.
+  Includes "Forward" and "Next" buttons and buttons for each page number.
 * [x] **Window**: a Frame with a title bar Frame on top.
   * Can be managed by Supervisor to give Window Manager controls to it
     (drag it by its title bar, Close button, window focus, multiple overlapping

pager.go

@@ -0,0 +1,213 @@
+package ui
+
+import (
+	"fmt"
+	"strconv"
+
+	"git.kirsle.net/go/render"
+)
+
+// Pager is a frame with Pagers for paginated UI.
+type Pager struct {
+	BaseWidget
+
+	// Config settings.
+	Page     int // default 1
+	Pages    int
+	PerPage  int // default 20
+	Font     render.Text
+	OnChange func(page, perPage int)
+
+	supervisor *Supervisor
+	child      Widget
+	buttons    []Widget
+	page       string // radio button value of Page
+
+	// Private options.
+	hovering bool
+	clicked  bool
+}
+
+// NewPager creates a new Pager.
+func NewPager(config Pager) *Pager {
+	w := &Pager{
+		Page:     config.Page,
+		Pages:    config.Pages,
+		PerPage:  config.PerPage,
+		Font:     config.Font,
+		OnChange: config.OnChange,
+		buttons:  []Widget{},
+	}
+
+	// default settings
+	if w.Page == 0 {
+		w.Page = 1
+	}
+	if w.PerPage == 0 {
+		w.PerPage = 20
+	}
+
+	w.IDFunc(func() string {
+		return fmt.Sprintf("Pager<%d of %d>", w.Page, w.PerPage)
+	})
+
+	w.child = w.setup()
+
+	return w
+}
+
+// Supervise the pager to make its buttons work.
+func (w *Pager) Supervise(s *Supervisor) {
+	w.supervisor = s
+	for _, btn := range w.buttons {
+		w.supervisor.Add(btn)
+	}
+}
+
+// setup the frame
+func (w *Pager) setup() *Frame {
+	frame := NewFrame("Pager Frame")
+	frame.SetParent(w)
+
+	if w.Pages == 0 {
+		return frame
+	}
+
+	w.buttons = []Widget{}
+	w.page = fmt.Sprintf("%d", w.Page)
+
+	// Previous Page Button
+	prev := NewButton("Previous", NewLabel(Label{
+		Text: "<",
+		Font: w.Font,
+	}))
+	w.buttons = append(w.buttons, prev)
+	prev.Handle(Click, func(ed EventData) error {
+		return w.next(-1)
+	})
+	frame.Pack(prev, Pack{
+		Side: W,
+	})
+
+	// Draw the numbered buttons.
+	for i := 1; i <= w.Pages; i++ {
+		page := fmt.Sprintf("%d", i)
+
+		btn := NewRadioButton(
+			"Page "+page,
+			&w.page,
+			page,
+			NewLabel(Label{
+				Text: page,
+				Font: w.Font,
+			}))
+		w.buttons = append(w.buttons, btn)
+
+		btn.Handle(Click, func(ed EventData) error {
+			if w.OnChange != nil {
+				page, _ := strconv.Atoi(w.page)
+				w.OnChange(page, w.PerPage)
+			}
+			return nil
+		})
+
+		if w.supervisor != nil {
+			w.supervisor.Add(btn)
+		}
+
+		frame.Pack(btn, Pack{
+			Side: W,
+		})
+	}
+
+	// Next Page Button
+	next := NewButton("Next", NewLabel(Label{
+		Text: ">",
+		Font: w.Font,
+	}))
+	w.buttons = append(w.buttons, next)
+	next.Handle(Click, func(ed EventData) error {
+		return w.next(1)
+	})
+	frame.Pack(next, Pack{
+		Side: W,
+	})
+
+	return frame
+}
+
+// next (1) or previous (-1) button
+func (w *Pager) next(value int) error {
+	fmt.Printf("next(%d)\n", value)
+	intvalue, _ := strconv.Atoi(w.page)
+	intvalue += value
+
+	if intvalue < 1 {
+		intvalue = 1
+	} else if intvalue > w.Pages {
+		intvalue = w.Pages
+	}
+
+	w.page = fmt.Sprintf("%d", intvalue)
+
+	if w.OnChange != nil {
+		w.OnChange(intvalue, w.PerPage)
+	}
+
+	return nil
+}
+
+// Compute the size of the Pager.
+func (w *Pager) Compute(e render.Engine) {
+	// Compute the size of the inner widget first.
+	w.child.Compute(e)
+
+	// Auto-resize only if we haven't been given a fixed size.
+	if !w.FixedSize() {
+		size := w.child.Size()
+		w.Resize(render.Rect{
+			W: size.W + w.BoxThickness(2),
+			H: size.H + w.BoxThickness(2),
+		})
+	}
+
+	w.BaseWidget.Compute(e)
+}
+
+// Present the Pager.
+func (w *Pager) Present(e render.Engine, P render.Point) {
+	if w.Hidden() {
+		return
+	}
+
+	w.Compute(e)
+	var (
+		S         = w.Size()
+		ChildSize = w.child.Size()
+	)
+
+	// Draw the widget's border and everything.
+	w.DrawBox(e, P)
+
+	// Offset further if we are currently sunken.
+	var clickOffset int
+	if w.clicked {
+		clickOffset++
+	}
+
+	// Where to place the child widget.
+	moveTo := render.Point{
+		X: P.X + w.BoxThickness(1) + clickOffset,
+		Y: P.Y + w.BoxThickness(1) + clickOffset,
+	}
+
+	// If we're bigger than we need to be, center the child widget.
+	if S.Bigger(ChildSize) {
+		moveTo.X = P.X + (S.W / 2) - (ChildSize.W / 2)
+	}
+
+	// Draw the text label inside.
+	w.child.Present(e, moveTo)
+
+	w.BaseWidget.Present(e, P)
+}