Added value changed event for slider.

Added flag for snapping to integer values.

ui/slider.go

@@ -11,7 +11,9 @@ type Slider struct {
 	Minimum     float32
 	Maximum     float32
 	Value       float32
+	Integer     bool
 
+	valueChanged func(float32)
 	handleWidth  float32
 	handle       sliderHandle
 }
@@ -34,11 +36,24 @@ func (s *Slider) handleDrag(pos geom.PointF32) {
 	} else {
 		offset = pos.Y
 	}
-	s.Value = s.Minimum + ((offset-start)/length)*(s.Maximum-s.Minimum)
+	s.setValue(s.Minimum + ((offset-start)/length)*(s.Maximum-s.Minimum))
+}
+
+func (s *Slider) setValue(v float32) {
 	if s.Minimum < s.Maximum {
-		s.Value = geom.Min32(s.Maximum, geom.Max32(s.Minimum, s.Value))
+		v = geom.Min32(s.Maximum, geom.Max32(s.Minimum, v))
 	} else {
-		s.Value = geom.Min32(s.Minimum, geom.Max32(s.Maximum, s.Value))
+		v = geom.Min32(s.Minimum, geom.Max32(s.Maximum, v))
+	}
+	if s.Integer {
+		v = geom.Round32(v)
+	}
+	if s.Value != v {
+		s.Value = v
+		valueChanged := s.valueChanged
+		if valueChanged != nil {
+			valueChanged(s.Value)
+		}
 	}
 }
 
@@ -97,6 +112,7 @@ func (s *Slider) DesiredSize(ctx Context) geom.PointF32 {
 func (s *Slider) Handle(ctx Context, e Event) {
 	s.handle.Handle(ctx, e)
 	s.ControlBase.Handle(ctx, e)
+	s.setValue(s.Value)
 }
 
 func (s *Slider) Render(ctx Context) {
@@ -111,6 +127,10 @@ func (s *Slider) Render(ctx Context) {
 	s.handle.Render(ctx)
 }
 
+func (s *Slider) OnValueChanged(fn func(float32)) {
+	s.valueChanged = fn
+}
+
 type sliderHandle struct {
 	ControlBase