Technical Doodad: Checkpoint Region

The Checkpoint Region acts as an invisible checkpoint flag, remembering
the player's location should they need to respawn there.

New cheat: `show all actors` during Play Mode will make every hidden
actor visible. Useful to see your technical doodads during gameplay!

Developer shell: `Execute(command string)` is available to the
JavaScript interpreter. It simulates another command being run on the
developer console.

dev-assets/doodads/regions/Makefile

@@ -6,6 +6,10 @@ build:
 	doodad convert -t "Goal Region" goal-128.png reg-goal.doodad
 	doodad install-script goal.js reg-goal.doodad
 
+	# Checkpoint Region
+	doodad convert -t "Checkpoint Region" checkpoint-128.png reg-checkpoint.doodad
+	doodad install-script checkpoint.js reg-checkpoint.doodad
+
 	# Fire Region
 	doodad convert -t "Fire Region" fire-128.png reg-fire.doodad
 	doodad install-script fire.js reg-fire.doodad

dev-assets/doodads/regions/checkpoint.js

@@ -0,0 +1,38 @@
+// Checkpoint Region
+// Acts like an invisible checkpoint flag.
+var isCurrentCheckpoint = false;
+
+function main() {
+    Self.Hide();
+    setActive(false);
+
+    // Checkpoints broadcast to all of their peers so they all
+    // know which one is the most recently activated.
+    Message.Subscribe("broadcast:checkpoint", function (currentID) {
+        setActive(false);
+    });
+
+    Events.OnCollide(function (e) {
+        if (isCurrentCheckpoint || !e.Settled) {
+            return;
+        }
+
+        // Only care about the player character.
+        if (!e.Actor.IsPlayer()) {
+            return;
+        }
+
+        // Set the player checkpoint.
+        SetCheckpoint(Self.Position());
+        setActive(true);
+        Message.Broadcast("broadcast:checkpoint", Self.ID())
+    });
+}
+
+function setActive(v) {
+    if (v && !isCurrentCheckpoint) {
+        Flash("Checkpoint!");
+    }
+
+    isCurrentCheckpoint = v;
+}