debugui: skip handling input and rendering widgets outside of scroll

Updates #41

Author: hajimehoshi

widget.go

@@ -119,6 +119,14 @@ func (c *Context) widget(id widgetID, opt option, layout func(bounds image.Recta
 		layout(bounds)
 	}
 
+	l, err := c.layout()
+	if err != nil {
+		return nil, err
+	}
+	if !l.body.Overlaps(bounds.Sub(c.currentContainer().layout.ScrollOffset)) {
+		return nil, nil
+	}
+
 	wasFocused := c.handleInputForWidget(id, bounds, opt)
 	var e EventHandler
 	if handleInput != nil {