code: func (ctr *rowConstructor) SpaceBegin(widget_count int) (bounds rect.Rect) {
  	layout := ctr.win.layout
  	panelLayout(ctr.win.ctx, ctr.win, ctr.height, widget_count, 0)
  	layout.Row.Type = layoutStaticFree
  
  	layout.Row.Ratio = nil
  	layout.Row.ItemWidth = 0
  	layout.Row.ItemRatio = 0.0
  	layout.Row.ItemOffset = 0
  	layout.Row.Filled = 0
  
  	style := ctr.win.style()
  	spacing := style.Spacing
  	padding := style.Padding
  
  	bounds.W = layout.Width - 2*padding.X
  	bounds.H = layout.Row.Height - spacing.Y
  
  	return bounds
  }
docs: // Starts new row that will contain widget_count widgets.
  // The size and position of widgets inside this row will be specified
  // by callling LayoutSpacePush/LayoutSpacePushScaled.