ludic.nav (18.5): a walker the crowd avoids and never moves

nav_crowd_add_fixed adds a walker with no steering, and nav_crowd_place puts it (snapped to the mesh) where the player is, with the velocity they have, each frame. The others plan round it by that velocity, and whatever it was pushed by is undone at the next placement. crowd_test: six walkers aimed through a standing player come no closer than 1.71 m and all get past, and the player stays where it was put. nav 16/16 on the Mac and the PC; DLL KERNEL32 only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.nav/tests/crowd_test.ludic

@@ -81,4 +81,39 @@ program CrowdTest {
     expect(not nav_crowd_read(nav_st, NAV_PERSON, a))
     expect_eq(nav_crowd_add(nav_st, NAV_PERSON, 5.0, 0.0, 5.0, 0.35, 1.8, 1.4, 0, 2.0), -1)
   }
+
+  test "a player standing in the way is walked round and never moved" (nav_st: mut NavState) {
+    expect(nav_build(nav_st, NAV_PERSON, ground(40, 0), new NavConfig))
+    expect(nav_crowd_start(nav_st, NAV_PERSON, 16, 0.6))
+    let me = nav_crowd_add_fixed(nav_st, NAV_PERSON, 20.0, 0.0, 20.0, 0.4, 1.8)
+    expect(me >= 0)
+    let ids = new []int
+    for i in 0 .. 6 {
+      let id = nav_crowd_add(nav_st, NAV_PERSON, 4.0, 0.0, 19.0 + float(i % 3), 0.35, 1.8, 1.4, 0, 2.0)
+      expect(nav_crowd_target(nav_st, NAV_PERSON, id, 36.0, 0.0, 19.0 + float(i % 3)))
+      push(ids, id)
+    }
+    var worst = 1000.0
+    for k in 0 .. 1800 {
+      expect(nav_crowd_place(nav_st, NAV_PERSON, me, 20.0, 0.0, 20.0, 0.0, 0.0))
+      nav_crowd_step(nav_st, 1.0 / 60.0)
+      for i in 0 .. len(ids) {
+        nav_crowd_read(nav_st, NAV_PERSON, ids[i])
+        let dx = nav_agent_x(nav_st) - 20.0
+        let dz = nav_agent_z(nav_st) - 20.0
+        worst = Math.min(worst, Math.sqrt(dx * dx + dz * dz))
+      }
+    }
+    nav_crowd_place(nav_st, NAV_PERSON, me, 20.0, 0.0, 20.0, 0.0, 0.0)
+    nav_crowd_read(nav_st, NAV_PERSON, me)
+    expect_near(nav_agent_x(nav_st), 20.0, 0.01)
+    var past = 0
+    for i in 0 .. len(ids) {
+      nav_crowd_read(nav_st, NAV_PERSON, ids[i])
+      if nav_agent_x(nav_st) > 34.0 { past += 1 }
+    }
+    print(`crowd: a walker came within {worst} m of the player (radii 0.75); {past} of 6 got past`)
+    expect(worst > 0.65)
+    expect_eq(past, 6)
+  }
 }