Port EcsDesc flag

Author: BeanCheeseBurrito

src/Flecs.NET.Tests/Cpp/QueryBuilderTests.cs

@@ -0,0 +1,71 @@
+using Flecs.NET.Core;
+using Xunit;
+
+namespace Flecs.NET.Tests.Cpp
+{
+    public class QueryBuilderTests
+    {
+        public QueryBuilderTests()
+        {
+            FlecsInternal.Reset();
+        }
+
+        [Fact]
+        public void CascadeDesc()
+        {
+            using World world = World.Create();
+
+            Entity tag = world.Entity();
+            Entity foo = world.Entity();
+            Entity bar = world.Entity();
+
+            Entity e0 = world.Entity().Add(tag);
+            Entity e1 = world.Entity().IsA(e0);
+            Entity e2 = world.Entity().IsA(e1);
+            Entity e3 = world.Entity().IsA(e2);
+
+            Query q = world.Query(
+                filter: world.FilterBuilder().With(tag).Cascade().Descend()
+            );
+
+            e1.Add(bar);
+            e2.Add(foo);
+
+            bool e1Found = false;
+            bool e2Found = false;
+            bool e3Found = false;
+
+            int count = 0;
+            q.Each((Entity e) =>
+            {
+                count ++;
+
+                if (e == e1) {
+                    Assert.False(e1Found);
+                    Assert.True(e2Found);
+                    Assert.True(e3Found);
+                    e1Found = true;
+                }
+
+                if (e == e2) {
+                    Assert.False(e1Found);
+                    Assert.False(e2Found);
+                    Assert.True(e3Found);
+                    e2Found = true;
+                }
+
+                if (e == e3) {
+                    Assert.False(e1Found);
+                    Assert.False(e2Found);
+                    Assert.False(e3Found);
+                    e3Found = true;
+                }
+            });
+
+            Assert.True(e1Found);
+            Assert.True(e2Found);
+            Assert.True(e3Found);
+            Assert.Equal(3, count);
+        }
+    }
+}

src/Flecs.NET/Core/Ecs.cs

@@ -310,6 +310,11 @@ public static partial class Ecs
         /// </summary>
         public const uint Cascade = EcsCascade;
 
+        /// <summary>
+        ///     Equivalent to <see cref="EcsDesc"/>
+        /// </summary>
+        public const uint Desc = EcsDesc;
+
         /// <summary>
         ///     Equivalent to <see cref="EcsParent"/>
         /// </summary>

src/Flecs.NET/Core/FilterBuilder.cs

@@ -160,6 +160,16 @@ public ref FilterBuilder Cascade<T>()
             return ref Cascade(Type<T>.Id(World));
         }
 
+        /// <summary>
+        ///     Use with cascade to iterate results in descending (bottom -> top) order
+        /// </summary>
+        /// <returns></returns>
+        public ref FilterBuilder Descend() {
+            AssertTermId();
+            CurrentTermId.flags |= EcsDesc;
+            return ref this;
+        }
+
         /// <summary>
         ///     The parent flag is short for Up(EcsChildOf).
         /// </summary>