layout: implement creation and return of the apex

Apex is the dot positioned at the center of a zone that is used to
terminate and tie any band ending in the zone.

src/layout/layout.rs

@@ -6,7 +6,7 @@ use crate::{
     drawing::{
         bend::LooseBendWeight,
         dot::{DotIndex, FixedDotIndex, FixedDotWeight, LooseDotIndex, LooseDotWeight},
-        graph::{PrimitiveIndex, PrimitiveWeight, Retag},
+        graph::{GetLayer, PrimitiveIndex, PrimitiveWeight, Retag},
         rules::RulesTrait,
         seg::{
             FixedSegIndex, FixedSegWeight, LoneLooseSegIndex, LoneLooseSegWeight, SeqLooseSegIndex,
@@ -17,16 +17,17 @@ use crate::{
         Drawing, Infringement, LayoutException,
     },
     geometry::{
-        compound::CompoundManagerTrait, poly::PolyShape, BendWeightTrait, DotWeightTrait,
-        GenericNode, Geometry, GeometryLabel, GetWidth, SegWeightTrait,
+        compound::CompoundManagerTrait, poly::PolyShape, shape::ShapeTrait, BendWeightTrait,
+        DotWeightTrait, GenericNode, Geometry, GeometryLabel, GetWidth, SegWeightTrait,
     },
     graph::{GenericIndex, GetNodeIndex},
     layout::{
         connectivity::{
             BandIndex, BandWeight, ConnectivityLabel, ConnectivityWeight, ContinentIndex,
         },
-        zone::{PourZoneIndex, SolidZoneIndex, Zone, ZoneWeight},
+        zone::{GetMaybeApex, MakePolyShape, PourZoneIndex, SolidZoneIndex, Zone, ZoneWeight},
     },
+    math::Circle,
 };
 
 pub type NodeIndex = GenericNode<PrimitiveIndex, GenericIndex<ZoneWeight>>;
@@ -207,6 +208,25 @@ impl<R: RulesTrait> Layout<R> {
             .compound_members(GenericIndex::new(zone.node_index()))
     }
 
+    pub fn zone_apex(&mut self, zone: GenericIndex<ZoneWeight>) -> FixedDotIndex {
+        if let Some(apex) = self.zone(zone).maybe_apex() {
+            apex
+        } else {
+            self.add_zone_fixed_dot(
+                FixedDotWeight {
+                    circle: Circle {
+                        pos: self.zone(zone).shape().center(),
+                        r: 0.0,
+                    },
+                    layer: self.zone(zone).layer(),
+                    maybe_net: None,
+                },
+                zone,
+            )
+            .unwrap()
+        }
+    }
+
     pub fn drawing(&self) -> &Drawing<ZoneWeight, R> {
         &self.drawing
     }

src/layout/zone.rs

@@ -5,9 +5,9 @@ use petgraph::stable_graph::NodeIndex;
 
 use crate::{
     drawing::{
-        dot::DotIndex,
+        dot::{DotIndex, FixedDotIndex},
         graph::{GetLayer, GetMaybeNet, MakePrimitive, PrimitiveIndex, PrimitiveWeight, Retag},
-        primitive::{GenericPrimitive, Primitive},
+        primitive::{GenericPrimitive, GetLimbs, Primitive},
         rules::RulesTrait,
         Drawing,
     },
@@ -21,6 +21,11 @@ pub trait MakePolyShape {
     fn shape(&self) -> PolyShape;
 }
 
+#[enum_dispatch]
+pub trait GetMaybeApex {
+    fn maybe_apex(&self) -> Option<FixedDotIndex>;
+}
+
 #[derive(Debug)]
 pub struct Zone<'a, R: RulesTrait> {
     pub index: GenericIndex<ZoneWeight>,
@@ -72,6 +77,26 @@ impl<'a, R: RulesTrait> MakePolyShape for Zone<'a, R> {
     }
 }
 
+impl<'a, R: RulesTrait> GetMaybeApex for Zone<'a, R> {
+    fn maybe_apex(&self) -> Option<FixedDotIndex> {
+        self.layout
+            .drawing()
+            .geometry()
+            .compound_members(self.index)
+            .find_map(|primitive_node| {
+                if let PrimitiveIndex::FixedDot(dot) = primitive_node {
+                    if self.layout.drawing().primitive(dot).segs().is_empty()
+                        && self.layout.drawing().primitive(dot).bends().is_empty()
+                    {
+                        return Some(dot);
+                    }
+                }
+
+                None
+            })
+    }
+}
+
 #[enum_dispatch(GetLayer, GetMaybeNet)]
 #[derive(Debug, Clone, Copy, PartialEq)]
 pub enum ZoneWeight {