Add examples catalog with subcommand dispatch

- Extract game engine from package main to engine/ library package
- Create examples/ package with registry, Entry type, and BuilderDeps
- Register default world as an example (moved from main())
- Add combat example: two teams of units facing each other
- Rewrite main.go as thin dispatch: go run . example [name]
- Update README with examples catalog one-liner

1 files changed, 46 insertions, 0 deletions

diff --git a/engine/patrol_order.go b/engine/patrol_order.go
new file mode 100644
index 0000000..0889f92
--- /dev/null
+++ b/engine/patrol_order.go
@@ -0,0 +1,46 @@
+package engine
+
+import (
+	"age_of_empires/ecs"
+	"age_of_empires/physics"
+
+	"golang.org/x/exp/slog"
+)
+
+type PatrolOrder struct {
+	origin      physics.Point
+	destination physics.Point
+}
+
+func UpdatePatrolSystem(moveMap physics.MoveMap, masks []ecs.Mask, orders []OrderKind, patrols []PatrolOrder, positions []physics.Point, moves []physics.Move) {
+	required := ecs.CM_Position | ecs.CM_Move | ecs.CM_Order | ecs.CM_PatrolOrder
+	for i, mask := range masks {
+		if mask&required == required {
+			order := orders[i]
+			patrol := patrols[i]
+			position := positions[i]
+			move := &moves[i]
+			if order == OrderKindPatrol && !move.IsActive {
+				if position == patrol.destination {
+					*move = physics.NewMove(position, patrol.origin, moveMap)
+				} else {
+					*move = physics.NewMove(position, patrol.destination, moveMap)
+				}
+			}
+		}
+	}
+}
+
+func StartPatrolSystem(destination physics.Point, masks []ecs.Mask, positions []physics.Point, moves []physics.Move, orders []OrderKind, patrols []PatrolOrder) {
+	required := ecs.CM_Position | ecs.CM_Order | ecs.CM_PatrolOrder
+	for i, mask := range masks {
+		if mask&required == required {
+			position := positions[i]
+			order := &orders[i]
+			patrol := &patrols[i]
+			slog.Info("patrolling between", slog.String("origin", position.String()), slog.String("destination", destination.String()))
+			*patrol = PatrolOrder{origin: position, destination: destination}
+			*order = OrderKindPatrol
+		}
+	}
+}