improve car/bike zordering when crossing z levels

game/src/render/bike.rs

@@ -94,10 +94,17 @@ impl DrawBike {
             );
         }
 
+        let zorder = input
+            .partly_on
+            .into_iter()
+            .chain(vec![input.on])
+            .map(|on| on.get_zorder(map))
+            .max()
+            .unwrap();
         DrawBike {
             id: input.id,
             body_circle,
-            zorder: input.on.get_zorder(map),
+            zorder,
             draw_default: prerender.upload(draw_default),
         }
     }

game/src/render/car.rs

@@ -150,11 +150,20 @@ impl DrawCar {
             );
         }
 
+        // TODO Technically some of the body may need to be at different zorders during
+        // transitions, but that's way too much effort
+        let zorder = input
+            .partly_on
+            .into_iter()
+            .chain(vec![input.on])
+            .map(|on| on.get_zorder(map))
+            .max()
+            .unwrap();
         DrawCar {
             id: input.id,
             body: input.body,
             body_polygon,
-            zorder: input.on.get_zorder(map),
+            zorder,
             draw_default: prerender.upload(draw_default),
         }
     }

sim/src/mechanics/car.rs

@@ -61,6 +61,7 @@ impl Car {
     ) -> DrawCarInput {
         assert!(front >= Distance::ZERO);
         // This goes from back to front
+        let mut partly_on = Vec::new();
         let raw_body = if front >= self.vehicle.length {
             self.router
                 .head()
@@ -83,6 +84,7 @@ impl Car {
                         self.vehicle.id, leftover
                     );
                 }
+                partly_on.push(self.last_steps[i]);
                 let len = self.last_steps[i].length(map);
                 let start = (len - leftover).max(Distance::ZERO);
                 let piece = self.last_steps[i]
@@ -215,6 +217,7 @@ impl Car {
                 CarState::Idling(_, _) => CarStatus::Parked,
             },
             on: self.router.head(),
+            partly_on,
             label: if self.vehicle.vehicle_type == VehicleType::Bus
                 || self.vehicle.vehicle_type == VehicleType::Train
             {

sim/src/mechanics/parking.rs

@@ -208,6 +208,7 @@ impl ParkingSimState {
                     waiting_for_turn: None,
                     status: CarStatus::Parked,
                     on: Traversable::Lane(lane),
+                    partly_on: Vec::new(),
                     label: None,
 
                     body: map
@@ -227,6 +228,7 @@ impl ParkingSimState {
                     status: CarStatus::Parked,
                     // Just used for z-order
                     on: Traversable::Lane(pl.driving_pos.lane()),
+                    partly_on: Vec::new(),
                     label: None,
 
                     body: PolyLine::must_new(vec![

sim/src/render.rs

@@ -34,7 +34,10 @@ pub struct DrawCarInput {
     pub id: CarID,
     pub waiting_for_turn: Option<TurnID>,
     pub status: CarStatus,
+    // Front of the car
     pub on: Traversable,
+    // Possibly the rest
+    pub partly_on: Vec<Traversable>,
     pub label: Option<String>,
 
     // Starts at the BACK of the car.