App/layers: deactivate surfaces on layers above.

* When activating a surface on layer x, all surfaces on all layers above
  this will be deactivated.
* Remove main_surface special case (we get the same result by putting
  the main_surface on the bottom layer).
* Track LayoutState per layer, make can_split() accept this layer-local
  LayoutState for its decision.
* Sort layers on load according to their ID. That is, do not make use
  Of the layer's z-order attribute, also there is no need to.

Signed-off-by: Marcus Fritzsch <marcus_fritzsch@mentor.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/layers.cpp b/src/layers.cpp
index d0a769a..a0665b7 100644
--- a/src/layers.cpp
+++ b/src/layers.cpp
@@ -87,7 +87,8 @@ struct result<struct layer_map> to_layer_map(nlohmann::json const &j) {
             return unsigned(k.layer_id);
          });
 
-      // XXX need to sort layers?
+      std::sort(stl.layers.begin(), stl.layers.end());
+
       for (auto i : stl.mapping) {
          if (i.name.empty()) {
             return Err<struct layer_map>("Found mapping w/o name");