Init state tick fix

Core/World/Entities/Definition/States/FrameState.cs

@@ -271,7 +271,7 @@ public void Tick(Entity entity)
             return;
 
         CurrentTick--;
-        if (CurrentTick <= 0)
+        if (CurrentTick == 0)
         {
             if (Frame.BranchType == ActorStateBranch.Stop && (Options & FrameStateOptions.DestroyOnStop) != 0)
             {

RELEASENOTES.md

@@ -27,6 +27,7 @@
 - Fix sky texture not working when it's not in the texture namespace.
 - Right-extend "block" characters in ENDOOM to emulate VGA "line graphics enable" mode.
 - Fix A_Refire not calling noise alert.
+- Match Doom behavior in the thing tick function that wouldn't advance the state for zero duration frames and leave them in a -1 loop.
 
 ## Misc:
 - Refactor of old Status Bar renderer to data-driven SBARDEF format.

Tests/Unit/GameAction/Dehacked/FrameStates.cs

@@ -0,0 +1,77 @@
+using FluentAssertions;
+using Helion.Geometry.Vectors;
+using Helion.Resources.IWad;
+using Helion.World.Impl.SinglePlayer;
+using Xunit;
+
+namespace Helion.Tests.Unit.GameAction.Dehacked;
+
+[Collection("GameActions")]
+public class FrameStates
+{
+    private readonly SinglePlayerWorld World;
+
+    public FrameStates()
+    {
+        World = WorldAllocator.LoadMap("Resources/box.zip", "box.WAD", "MAP01", GetType().Name, (world) => { }, IWadType.Doom2);
+    }
+
+    [Fact(DisplayName = "Setting null death state through missile removes entity")]
+    public void NullDeathStateRemovesEntity()
+    {
+        var def = World.EntityManager.DefinitionComposer.GetByName("DoomImp")!;
+        def.DeathState = null;
+        def.Flags.SetSpawnCeiling();
+        def.Flags.SetMissile();
+
+        var entity = GameActions.CreateEntity(World, "DoomImp", Vec3D.Zero, initSpawn: true);
+        entity.IsDisposed.Should().BeFalse();
+        GameActions.TickWorld(World, 35);
+        entity.IsDisposed.Should().BeTrue();
+    }
+
+    [Fact(DisplayName = "Zero tick duration spawn state set -1 and loops")]
+    public void ZeroTickDurationSpawnState()
+    {
+        // The tick function didn't have the same check and wouldn't let a zero duration frame immediately go to the next.
+        // It would decrement and check if it didn't equal zero and this causes it to be infinitely in a -1 frame.
+        var def = World.EntityManager.DefinitionComposer.GetByName("DoomImp")!;
+        var frame = World.ArchiveCollection.EntityFrameTable.Frames[def.SpawnState!.Value];
+        frame.Ticks = 0;
+        frame.NextFrameIndex = frame.MasterFrameIndex;
+
+        var entity = GameActions.CreateEntity(World, "DoomImp", Vec3D.Zero, initSpawn: true);
+        entity.FrameState.Frame.Should().Be(frame);
+        entity.FrameState.CurrentTick.Should().Be(0);
+        entity.Tick();
+        entity.FrameState.Frame.Should().Be(frame);
+        entity.FrameState.CurrentTick.Should().Be(-1);
+        entity.Tick();
+        entity.FrameState.Frame.Should().Be(frame);
+        entity.FrameState.CurrentTick.Should().Be(-1);
+    }
+
+    [Fact(DisplayName = "Zero tick duration after spawn state automatically goes to next frame")]
+    public void ZeroTickDurationAfterSpawnState()
+    {
+        var def = World.EntityManager.DefinitionComposer.GetByName("DoomImp")!;
+        var frame = World.ArchiveCollection.EntityFrameTable.Frames[def.SpawnState!.Value];
+        frame.ActionFunction = null;
+        frame.Ticks = 1;
+        frame.NextFrameIndex = frame.MasterFrameIndex + 1;
+        var nextFrame = frame.NextFrame;
+        nextFrame.ActionFunction = null;
+        nextFrame.Ticks = 0;
+        nextFrame.NextFrameIndex = nextFrame.MasterFrameIndex + 1;
+        var lastFrame = nextFrame.NextFrame;
+        lastFrame.ActionFunction = null;
+        lastFrame.Ticks = 69;
+
+        var entity = GameActions.CreateEntity(World, "DoomImp", Vec3D.Zero, initSpawn: true);
+        entity.FrameState.Frame.Should().Be(frame);
+        entity.FrameState.CurrentTick.Should().Be(1);
+        entity.Tick();
+        entity.FrameState.Frame.Should().Be(lastFrame);
+        entity.FrameState.CurrentTick.Should().Be(69);
+    }
+}