Solution precision fixes (#25199)

* Add test for two chemistry issues

1. rounding issue with reaction processing when making chloral hydrate
2. reliable assert trip due to the ValidateSolution() heat capacity issue.

* Fix FixedPoint2 arithmetic

Fix internal floating point arithmetic in places where it could be avoided.

Fix incorrect rounding mode used in other places (it should always floor, like regular int arithmetic).

I had to add an explicit epsilon value for float -> FixedPoint2 because something like 1.05 is actually like 1.04999 and that'd cause it to be rounded down to 1.04.

This fixes reaction reagent processing in cases where the reagent inputs can't cleanly divide. Previously, when making 30u chloral hydrate by adding the chlorine in 10u increments you'd end up with 0.04 chlorine left over. This was caused by division in the reaction code rounding up in some cases. Changing division here to always round down fixes it.

* Attempt to fix heat capacity precision assert issues.

Fixes #22126

First, we just increase the tolerance of the assert. It was way too low.

Second, actually put a cap on float drift from one-off _heatCapacity changes.

* Fix float -> FixedPoint2 epsilon for negative number, fix tests.

* Fix DamageableTest

* Oh yeah I need to call CleanReturnAsync

Content.IntegrationTests/Tests/Chemistry/SolutionRoundingTest.cs

@@ -0,0 +1,122 @@
+using Content.Server.Chemistry.Containers.EntitySystems;
+using Content.Shared.Chemistry.Components;
+using Content.Shared.Chemistry.Reaction;
+using Content.Shared.Chemistry.Reagent;
+using Content.Shared.FixedPoint;
+using Robust.Shared.GameObjects;
+
+namespace Content.IntegrationTests.Tests.Chemistry;
+
+[TestFixture]
+[TestOf(typeof(ChemicalReactionSystem))]
+public sealed class SolutionRoundingTest
+{
+    // This test tests two things:
+    // * A rounding error in reaction code while I was making chloral hydrate
+    // * An assert with solution heat capacity calculations that I found a repro for while testing the above.
+
+    [TestPrototypes]
+    private const string Prototypes = @"
+- type: entity
+  id: SolutionRoundingTestContainer
+  components:
+  - type: SolutionContainerManager
+    solutions:
+      beaker:
+        maxVol: 100
+
+# This is the Chloral Hydrate recipe fyi.
+- type: reagent
+  id: SolutionRoundingTestReagentA
+  name: reagent-name-nothing
+  desc: reagent-desc-nothing
+  physicalDesc: reagent-physical-desc-nothing
+
+- type: reagent
+  id: SolutionRoundingTestReagentB
+  name: reagent-name-nothing
+  desc: reagent-desc-nothing
+  physicalDesc: reagent-physical-desc-nothing
+
+- type: reagent
+  id: SolutionRoundingTestReagentC
+  name: reagent-name-nothing
+  desc: reagent-desc-nothing
+  physicalDesc: reagent-physical-desc-nothing
+
+- type: reagent
+  id: SolutionRoundingTestReagentD
+  name: reagent-name-nothing
+  desc: reagent-desc-nothing
+  physicalDesc: reagent-physical-desc-nothing
+
+- type: reaction
+  id: SolutionRoundingTestReaction
+  impact: Medium
+  reactants:
+    SolutionRoundingTestReagentA:
+      amount: 3
+    SolutionRoundingTestReagentB:
+      amount: 1
+    SolutionRoundingTestReagentC:
+      amount: 1
+  products:
+    SolutionRoundingTestReagentD: 1
+";
+
+    [Test]
+    public async Task Test()
+    {
+        await using var pair = await PoolManager.GetServerClient();
+        var server = pair.Server;
+        var testMap = await pair.CreateTestMap();
+
+        Solution solution = default;
+        Entity<SolutionComponent> solutionEnt = default;
+
+        await server.WaitPost(() =>
+        {
+            var system = server.System<SolutionContainerSystem>();
+            var beaker = server.EntMan.SpawnEntity("SolutionRoundingTestContainer", testMap.GridCoords);
+
+            system.TryGetSolution(beaker, "beaker", out var newSolutionEnt, out var newSolution);
+
+            solutionEnt = newSolutionEnt!.Value;
+            solution = newSolution!;
+
+            system.TryAddSolution(solutionEnt, new Solution("SolutionRoundingTestReagentC", 50));
+            system.TryAddSolution(solutionEnt, new Solution("SolutionRoundingTestReagentB", 30));
+
+            for (var i = 0; i < 9; i++)
+            {
+                system.TryAddSolution(solutionEnt, new Solution("SolutionRoundingTestReagentA", 10));
+            }
+        });
+
+        await server.WaitAssertion(() =>
+        {
+            Assert.Multiple(() =>
+            {
+                Assert.That(
+                    solution.ContainsReagent("SolutionRoundingTestReagentA", null),
+                    Is.False,
+                    "Solution should not contain reagent A");
+
+                Assert.That(
+                    solution.ContainsReagent("SolutionRoundingTestReagentB", null),
+                    Is.False,
+                    "Solution should not contain reagent B");
+
+                Assert.That(
+                    solution![new ReagentId("SolutionRoundingTestReagentC", null)].Quantity,
+                    Is.EqualTo((FixedPoint2) 20));
+
+                Assert.That(
+                    solution![new ReagentId("SolutionRoundingTestReagentD", null)].Quantity,
+                    Is.EqualTo((FixedPoint2) 30));
+            });
+        });
+
+        await pair.CleanReturnAsync();
+    }
+}

Content.IntegrationTests/Tests/Damageable/DamageableTest.cs

@@ -170,19 +170,19 @@ namespace Content.IntegrationTests.Tests.Damageable
 
                 // Check that damage works properly if it is NOT perfectly divisible among group members
                 types = group3.DamageTypes;
-                damageToDeal = FixedPoint2.New(types.Count * 5 - 1);
+
-                damage = new DamageSpecifier(group3, damageToDeal);
+                Assert.That(types, Has.Count.EqualTo(3));
+
+                damage = new DamageSpecifier(group3, 14);
                 sDamageableSystem.TryChangeDamage(uid, damage, true);
 
                 Assert.Multiple(() =>
                 {
-                    Assert.That(sDamageableComponent.TotalDamage, Is.EqualTo(damageToDeal));
+                    Assert.That(sDamageableComponent.TotalDamage, Is.EqualTo(FixedPoint2.New(14)));
-                    Assert.That(sDamageableComponent.DamagePerGroup[group3.ID], Is.EqualTo(damageToDeal));
+                    Assert.That(sDamageableComponent.DamagePerGroup[group3.ID], Is.EqualTo(FixedPoint2.New(14)));
-                    Assert.That(sDamageableComponent.Damage.DamageDict[type3a.ID], Is.EqualTo(damageToDeal / types.Count));
+                    Assert.That(sDamageableComponent.Damage.DamageDict[type3a.ID], Is.EqualTo(FixedPoint2.New(4.66f)));
-                    Assert.That(sDamageableComponent.Damage.DamageDict[type3b.ID], Is.EqualTo(damageToDeal / types.Count));
+                    Assert.That(sDamageableComponent.Damage.DamageDict[type3b.ID], Is.EqualTo(FixedPoint2.New(4.67f)));
-
+                    Assert.That(sDamageableComponent.Damage.DamageDict[type3c.ID], Is.EqualTo(FixedPoint2.New(4.67f)));
-                    // last one will get 0.01 less, since its not perfectly divisble by 3
-                    Assert.That(sDamageableComponent.Damage.DamageDict[type3c.ID], Is.EqualTo(damageToDeal / types.Count - 0.01));
                 });
 
                 // Heal
@@ -224,7 +224,7 @@ namespace Content.IntegrationTests.Tests.Damageable
 
                 Assert.Multiple(() =>
                 {
-                    Assert.That(sDamageableComponent.Damage.DamageDict[type3a.ID], Is.EqualTo(FixedPoint2.New(1.33)));
+                    Assert.That(sDamageableComponent.Damage.DamageDict[type3a.ID], Is.EqualTo(FixedPoint2.New(1.34)));
                     Assert.That(sDamageableComponent.Damage.DamageDict[type3b.ID], Is.EqualTo(FixedPoint2.New(3.33)));
                     Assert.That(sDamageableComponent.Damage.DamageDict[type3c.ID], Is.EqualTo(FixedPoint2.New(0)));
                 });

Content.Shared/Chemistry/Components/Solution.cs

@@ -92,6 +92,12 @@ namespace Content.Shared.Chemistry.Components
         /// </summary>
         [ViewVariables] private bool _heatCapacityDirty = true;
 
+        [ViewVariables(VVAccess.ReadWrite)]
+        private int _heatCapacityUpdateCounter;
+
+        // This value is arbitrary btw.
+        private const int HeatCapacityUpdateInterval = 15;
+
         public void UpdateHeatCapacity(IPrototypeManager? protoMan)
         {
             IoCManager.Resolve(ref protoMan);
@@ -103,6 +109,8 @@ namespace Content.Shared.Chemistry.Components
                 _heatCapacity += (float) quantity *
                                     protoMan.Index<ReagentPrototype>(reagent.Prototype).SpecificHeat;
             }
+
+            _heatCapacityUpdateCounter = 0;
         }
 
         public float GetHeatCapacity(IPrototypeManager? protoMan)
@@ -112,6 +120,15 @@ namespace Content.Shared.Chemistry.Components
             return _heatCapacity;
         }
 
+        public void CheckRecalculateHeatCapacity()
+        {
+            // For performance, we have a few ways for heat capacity to get modified without a full recalculation.
+            // To avoid these drifting too much due to float error, we mark it as dirty after N such operations,
+            // so it will be recalculated.
+            if (++_heatCapacityUpdateCounter >= HeatCapacityUpdateInterval)
+                _heatCapacityDirty = true;
+        }
+
         public float GetThermalEnergy(IPrototypeManager? protoMan)
         {
             return GetHeatCapacity(protoMan) * Temperature;
@@ -165,6 +182,7 @@ namespace Content.Shared.Chemistry.Components
             Temperature = solution.Temperature;
             _heatCapacity = solution._heatCapacity;
             _heatCapacityDirty = solution._heatCapacityDirty;
+            _heatCapacityUpdateCounter = solution._heatCapacityUpdateCounter;
             ValidateSolution();
         }
 
@@ -193,7 +211,7 @@ namespace Content.Shared.Chemistry.Components
                 var cur = _heatCapacity;
                 _heatCapacityDirty = true;
                 UpdateHeatCapacity(null);
-                DebugTools.Assert(MathHelper.CloseTo(_heatCapacity, cur));
+                DebugTools.Assert(MathHelper.CloseTo(_heatCapacity, cur, tolerance: 0.01));
             }
     #endif
         }
@@ -380,7 +398,9 @@ namespace Content.Shared.Chemistry.Components
         public void AddReagent(ReagentPrototype proto, ReagentId reagentId, FixedPoint2 quantity)
         {
             AddReagent(reagentId, quantity, false);
+
             _heatCapacity += quantity.Float() * proto.SpecificHeat;
+            CheckRecalculateHeatCapacity();
         }
 
         public void AddReagent(ReagentQuantity reagentQuantity)
@@ -419,6 +439,7 @@ namespace Content.Shared.Chemistry.Components
 
             _heatCapacity *= scale;
             Volume *= scale;
+            CheckRecalculateHeatCapacity();
 
             for (int i = 0; i < Contents.Count; i++)
             {
@@ -752,6 +773,7 @@ namespace Content.Shared.Chemistry.Components
             }
 
             _heatCapacity += otherSolution._heatCapacity;
+            CheckRecalculateHeatCapacity();
             if (closeTemps)
                 _heatCapacityDirty |= otherSolution._heatCapacityDirty;
             else

Content.Shared/FixedPoint/FixedPoint2.cs

@@ -20,6 +20,9 @@ namespace Content.Shared.FixedPoint
         public static FixedPoint2 Epsilon { get; } = new(1);
         public static FixedPoint2 Zero { get; } = new(0);
 
+        // This value isn't picked by any proper testing, don't @ me.
+        private const float FloatEpsilon = 0.00001f;
+
 #if DEBUG
         static FixedPoint2()
         {
@@ -47,7 +50,17 @@ namespace Content.Shared.FixedPoint
 
         public static FixedPoint2 New(float value)
         {
-            return new((int) MathF.Round(value * ShiftConstant, MidpointRounding.AwayFromZero));
+            return new((int) ApplyFloatEpsilon(value * ShiftConstant));
+        }
+
+        private static float ApplyFloatEpsilon(float value)
+        {
+            return value + FloatEpsilon * Math.Sign(value);
+        }
+
+        private static double ApplyFloatEpsilon(double value)
+        {
+            return value + FloatEpsilon * Math.Sign(value);
         }
 
         /// <summary>
@@ -60,17 +73,12 @@ namespace Content.Shared.FixedPoint
 
         public static FixedPoint2 New(double value)
         {
-            return new((int) Math.Round(value * ShiftConstant, MidpointRounding.AwayFromZero));
+            return new((int) ApplyFloatEpsilon(value * ShiftConstant));
         }
 
         public static FixedPoint2 New(string value)
         {
-            return New(FloatFromString(value));
+            return New(Parse.Float(value));
-        }
-
-        private static float FloatFromString(string value)
-        {
-            return float.Parse(value, CultureInfo.InvariantCulture);
         }
 
         public static FixedPoint2 operator +(FixedPoint2 a) => a;
@@ -85,17 +93,17 @@ namespace Content.Shared.FixedPoint
 
         public static FixedPoint2 operator *(FixedPoint2 a, FixedPoint2 b)
         {
-            return new((int) MathF.Round(b.Value * a.Value / (float) ShiftConstant, MidpointRounding.AwayFromZero));
+            return new(b.Value * a.Value / ShiftConstant);
         }
 
         public static FixedPoint2 operator *(FixedPoint2 a, float b)
         {
-            return new((int) MathF.Round(a.Value * b, MidpointRounding.AwayFromZero));
+            return new((int) ApplyFloatEpsilon(a.Value * b));
         }
 
         public static FixedPoint2 operator *(FixedPoint2 a, double b)
         {
-            return new((int) Math.Round(a.Value * b, MidpointRounding.AwayFromZero));
+            return new((int) ApplyFloatEpsilon(a.Value * b));
         }
 
         public static FixedPoint2 operator *(FixedPoint2 a, int b)
@@ -105,12 +113,12 @@ namespace Content.Shared.FixedPoint
 
         public static FixedPoint2 operator /(FixedPoint2 a, FixedPoint2 b)
         {
-            return new((int) MathF.Round((ShiftConstant * a.Value) / (float) b.Value, MidpointRounding.AwayFromZero));
+            return new((int) (ShiftConstant * (long) a.Value / b.Value));
         }
 
         public static FixedPoint2 operator /(FixedPoint2 a, float b)
         {
-            return new((int) MathF.Round(a.Value / b, MidpointRounding.AwayFromZero));
+            return new((int) ApplyFloatEpsilon(a.Value / b));
         }
 
         public static bool operator <=(FixedPoint2 a, int b)
@@ -185,7 +193,7 @@ namespace Content.Shared.FixedPoint
 
         public readonly int Int()
         {
-            return (int) ShiftDown();
+            return Value / ShiftConstant;
         }
 
         // Implicit operators ftw
@@ -266,7 +274,7 @@ namespace Content.Shared.FixedPoint
             if (value == "MaxValue")
                 Value = int.MaxValue;
             else
-                this = New(FloatFromString(value));
+                this = New(Parse.Float(value));
         }
 
         public override readonly string ToString() => $"{ShiftDown().ToString(CultureInfo.InvariantCulture)}";

Content.Tests/Shared/Chemistry/FixedPoint2_Tests.cs

@@ -4,7 +4,7 @@ using NUnit.Framework;
 
 namespace Content.Tests.Shared.Chemistry
 {
-    [TestFixture, TestOf(typeof(FixedPoint2))]
+    [TestFixture, TestOf(typeof(FixedPoint2)), Parallelizable]
     public sealed class FixedPoint2_Tests
     {
         [Test]
@@ -18,8 +18,11 @@ namespace Content.Tests.Shared.Chemistry
         }
 
         [Test]
-        [TestCase(1.001f, "1")]
+        [TestCase(0.999f, "0.99")]
-        [TestCase(0.999f, "1")]
+        [TestCase(1.005f, "1")]
+        [TestCase(1.015f, "1.01")]
+        [TestCase(1.05f, "1.05")]
+        [TestCase(-1.05f, "-1.05")]
         public void FixedPoint2FloatTests(float value, string expected)
         {
             var result = FixedPoint2.New(value);
@@ -27,8 +30,10 @@ namespace Content.Tests.Shared.Chemistry
         }
 
         [Test]
-        [TestCase(1.001d, "1")]
+        [TestCase(0.999, "0.99")]
-        [TestCase(0.999d, "1")]
+        [TestCase(1.005, "1")]
+        [TestCase(1.015, "1.01")]
+        [TestCase(1.05, "1.05")]
         public void FixedPoint2DoubleTests(double value, string expected)
         {
             var result = FixedPoint2.New(value);
@@ -36,8 +41,10 @@ namespace Content.Tests.Shared.Chemistry
         }
 
         [Test]
-        [TestCase("1.005", "1.01")]
+        [TestCase("0.999", "0.99")]
-        [TestCase("0.999", "1")]
+        [TestCase("1.005", "1")]
+        [TestCase("1.015", "1.01")]
+        [TestCase("1.05", "1.05")]
         public void FixedPoint2StringTests(string value, string expected)
         {
             var result = FixedPoint2.New(value);
@@ -45,11 +52,9 @@ namespace Content.Tests.Shared.Chemistry
         }
 
         [Test]
-        [TestCase(1.001f, 1.001f, "2")]
+        [TestCase(1, 1, "2")]
-        [TestCase(1.001f, 1.004f, "2")]
+        [TestCase(1.05f, 1, "2.05")]
-        [TestCase(1f, 1.005f, "2.01")]
+        public void ArithmeticAddition(float aFloat, float bFloat, string expected)
-        [TestCase(1f, 2.005f, "3.01")]
-        public void CalculusPlus(float aFloat, float bFloat, string expected)
         {
             var a = FixedPoint2.New(aFloat);
             var b = FixedPoint2.New(bFloat);
@@ -60,10 +65,9 @@ namespace Content.Tests.Shared.Chemistry
         }
 
         [Test]
-        [TestCase(1.001f, 1.001f, "0")]
+        [TestCase(1, 1, "0")]
-        [TestCase(1.001f, 1.004f, "0")]
+        [TestCase(1f, 2.5f, "-1.5")]
-        [TestCase(1f, 2.005f, "-1.01")]
+        public void ArithmeticSubtraction(float aFloat, float bFloat, string expected)
-        public void CalculusMinus(float aFloat, float bFloat, string expected)
         {
             var a = FixedPoint2.New(aFloat);
             var b = FixedPoint2.New(bFloat);
@@ -77,7 +81,8 @@ namespace Content.Tests.Shared.Chemistry
         [TestCase(1.001f, 3f, "0.33")]
         [TestCase(0.999f, 3f, "0.33")]
         [TestCase(2.1f, 3f, "0.7")]
-        public void CalculusDivision(float aFloat, float bFloat, string expected)
+        [TestCase(0.03f, 2f, "0.01")]
+        public void ArithmeticDivision(float aFloat, float bFloat, string expected)
         {
             var a = FixedPoint2.New(aFloat);
             var b = FixedPoint2.New(bFloat);
@@ -88,9 +93,24 @@ namespace Content.Tests.Shared.Chemistry
         }
 
         [Test]
-        [TestCase(1.001f, 0.999f, "1")]
+        [TestCase(1.001f, 3f, "0.33")]
-        [TestCase(0.999f, 3f, "3")]
+        [TestCase(0.999f, 3f, "0.33")]
-        public void CalculusMultiplication(float aFloat, float bFloat, string expected)
+        [TestCase(2.1f, 3f, "0.7")]
+        [TestCase(0.03f, 2f, "0.01")]
+        [TestCase(1f, 1 / 1.05f, "1.05")]
+        public void ArithmeticDivisionFloat(float aFloat, float b, string expected)
+        {
+            var a = FixedPoint2.New(aFloat);
+
+            var result = a / b;
+
+            Assert.That($"{result}", Is.EqualTo(expected));
+        }
+
+        [Test]
+        [TestCase(1, 1, "1")]
+        [TestCase(1, 3f, "3")]
+        public void ArithmeticMultiplication(float aFloat, float bFloat, string expected)
         {
             var a = FixedPoint2.New(aFloat);
             var b = FixedPoint2.New(bFloat);
@@ -100,6 +120,17 @@ namespace Content.Tests.Shared.Chemistry
             Assert.That($"{result}", Is.EqualTo(expected));
         }
 
+        [Test]
+        [TestCase(1, 1, "1")]
+        [TestCase(1, 1.05f, "1.05")]
+        public void ArithmeticMultiplicationFloat(float aFloat, float b, string expected)
+        {
+            var a = FixedPoint2.New(aFloat);
+            var result = a * b;
+
+            Assert.That($"{result}", Is.EqualTo(expected));
+        }
+
         [Test]
         [TestCase(0.995f, 100)]
         [TestCase(1.005f, 101)]

Content.Tests/Shared/DamageTest.cs

@@ -121,9 +121,9 @@ namespace Content.Tests.Shared
             damageSpec = new(_prototypeManager.Index<DamageGroupPrototype>("Brute"), 4);
             Assert.That(damageSpec.DamageDict.TryGetValue("Blunt", out damage));
             Assert.That(damage, Is.EqualTo(FixedPoint2.New(1.33)));
-            Assert.That(damageSpec.DamageDict.TryGetValue("Piercing", out damage));
-            Assert.That(damage, Is.EqualTo(FixedPoint2.New(1.33)));
             Assert.That(damageSpec.DamageDict.TryGetValue("Slash", out damage));
+            Assert.That(damage, Is.EqualTo(FixedPoint2.New(1.33)));
+            Assert.That(damageSpec.DamageDict.TryGetValue("Piercing", out damage));
             Assert.That(damage, Is.EqualTo(FixedPoint2.New(1.34))); // doesn't divide evenly, so the 0.01 goes to the last one
 
             damageSpec = new(_prototypeManager.Index<DamageTypePrototype>("Piercing"), 4);
@@ -161,7 +161,7 @@ namespace Content.Tests.Shared
             Assert.That(damageSpec.DamageDict["Blunt"], Is.EqualTo(FixedPoint2.New(30)));
             Assert.That(damageSpec.DamageDict["Piercing"], Is.EqualTo(FixedPoint2.New(-40))); // resistances don't apply to healing
             Assert.That(!damageSpec.DamageDict.ContainsKey("Slash"));  // Reduction reduced to 0, and removed from specifier
-            Assert.That(damageSpec.DamageDict["Radiation"], Is.EqualTo(FixedPoint2.New(65.63)));
+            Assert.That(damageSpec.DamageDict["Radiation"], Is.EqualTo(FixedPoint2.New(65.62)));
         }
 
         // Default damage Yaml