Added ProgressBar and implemented it on GTK+.

basicctrls.go

@@ -147,7 +147,6 @@ func NewTextbox() Textbox {
 // - TODO set page step?
 // - TODO wrapping
 // - TODO negative values
-// - TODO ensuring values entered in text box stay within bounds (OS X seems to take care of this automatically; not sure about Windows or GTK+...)
 type Spinbox interface {
 	Control
 
@@ -170,3 +169,19 @@ func NewSpinbox(min int, max int) Spinbox {
 	}
 	return newSpinbox(min, max)
 }
+
+// ProgressBar is a Control that displays a horizontal bar which shows the level of completion of an operation.
+type ProgressBar interface {
+	Control
+
+	// Percent and SetPrecent get and set the current percentage indicated by the ProgressBar, respectively.
+	// This value must be between 0 and 100; all other values cause SetPercent to panic.
+	Percent() int
+	SetPercent(percent int)
+}
+
+// NewProgressBar creates a new ProgressBar.
+// It will initially show a progress of 0%.
+func NewProgressBar() ProgressBar {
+	return newProgressBar()
+}

zz_test.go

@@ -150,11 +150,11 @@ func (tw *testwin) addfe() {
 	tw.festack.SetStretchy(4)
 	tw.festack.SetStretchy(6)
 	sb := NewSpinbox(0, 100)
-	sl := NewLabel("")
+	sp := NewProgressBar()
 	sb.OnChanged(func() {
-		sl.SetText(fmt.Sprintf("%d", sb.Value()))
+		sp.SetPercent(sb.Value())
 	})
-	tw.festack2 = newVerticalStack(sb, sl, Space(), Space(), NewTextbox())
+	tw.festack2 = newVerticalStack(sb, sp, Space(), Space(), NewTextbox())
 	tw.festack2.SetStretchy(3)
 	tw.festack2.SetStretchy(4)
 	tw.festack = newHorizontalStack(tw.festack, tw.festack2)