Fix terrain streaming and surface spawning

internal/server/spawner_test.go

@@ -0,0 +1,39 @@
+package server
+
+import (
+	"math"
+	"math/rand"
+	"testing"
+
+	"regionio/internal/world"
+)
+
+func TestSpawnMobNearPlayerUsesSurface(t *testing.T) {
+	cfg := DefaultConfig()
+	cfg.WorldDir = ""
+	srv, err := NewWithCache(cfg, world.NewCache(-1, world.GenerateFlat))
+	if err != nil {
+		t.Fatal(err)
+	}
+	session, err := srv.RegisterPlayer(Profile{Name: "Alice", UUID: OfflineUUID("Alice")}, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	srv.SetPlayerTransform(session, 8.5, 80, 8.5, 0, 0, true)
+
+	if !srv.spawnMobNearPlayer(rand.New(rand.NewSource(1)), 10, 20) {
+		t.Fatal("spawnMobNearPlayer returned false")
+	}
+	entities := srv.Entities().All()
+	if len(entities) != 1 {
+		t.Fatalf("entities = %d, want 1", len(entities))
+	}
+	entity := entities[0]
+	if entity.Y != world.FlatSurfaceY+1 {
+		t.Fatalf("mob Y = %v, want surface Y %d", entity.Y, world.FlatSurfaceY+1)
+	}
+	distance := math.Hypot(entity.X-8.5, entity.Z-8.5)
+	if distance < 15 || distance > 33 {
+		t.Fatalf("mob distance = %v, want near player", distance)
+	}
+}