Scenario viewpoint, Z index management, and arrow controls

internal/scenario/manage.go

@@ -13,3 +13,16 @@ func (s *Scenario) CellAtCursor() (maps.Cell, CellPoint) {
 	cell := s.area.Cell(int(s.selectedCell.X), int(s.selectedCell.Y), 0)
 	return cell, CellPoint{IsoPt: s.selectedCell, Z: 0}
 }
+
+func (s *Scenario) ChangeZIdx(by int) {
+	newZ := s.ZIdx + by
+	if newZ < 0 {
+		newZ = 0
+	}
+
+	if newZ > 6 {
+		newZ = 6
+	}
+
+	s.ZIdx = newZ
+}