Fix offset when 3D sector is above upper wall

Core/Render/OpenGL/Renderers/Legacy/World/Geometry/GeometryRenderer.Sector3D.cs

@@ -225,8 +225,18 @@ public RenderWallSliceResult RenderWallSlices3D(Side side, Wall wall, bool isFro
 
         var renderThrough = style != RenderDataStyle.Normal;
         SectorPlane3D? lastPlane3D = null;
-        SetWallOffset(m_fakeSide, m_fakeWall, offsetY, GetStartAnchorZ(side, wall, otherSector, wallHeights3D), anchorZ, prevAnchorZ);
 
+        double addOffsetZ = 0;
+        double prevAddOffsetZ = 0;
+        // If this 3D sector is above the first plane then add the offset since it's not traversed. This happens when an upper is covering a 3D sector.
+        if (wallHeights3D != null && traversePlanes3D.Length > 0 && (wallHeights3D.Value.TopZ > traversePlanes3D[0].Plane.Z || wallHeights3D.Value.PrevTopZ > traversePlanes3D[0].Plane.PrevZ))
+        {
+            addOffsetZ = wallHeights3D.Value.TopZ - traversePlanes3D[0].Plane.Z;
+            prevAddOffsetZ = wallHeights3D.Value.PrevTopZ - traversePlanes3D[0].Plane.PrevZ;
+        }
+
+        SetWallOffset(m_fakeSide, m_fakeWall, offsetY, GetStartAnchorZ(side, wall, otherSector, wallHeights3D), anchorZ, prevAnchorZ, addOffsetZ, prevAddOffsetZ);
+
         for (int i = 0; i < traversePlanes3D.Length - 1; i++)
         {
             ref var plane3D = ref traversePlanes3D[i];
@@ -384,11 +394,11 @@ private static SectorPlane CalculateAnchorPlane(Side side, Wall wall, Sector oth
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    private static void SetWallOffset(Side side, Wall wall, float saveOffsetY, SectorPlane top, double anchorZ, double prevAnchorZ)
+    private static void SetWallOffset(Side side, Wall wall, float saveOffsetY, SectorPlane top, double anchorZ, double prevAnchorZ, double addOffsetZ = 0, double prevAddOffsetZ = 0)
     {
         // Use scrolling data for offset since normal wall offsets can't interpolate
-        side.ScrollData!.Offset(wall.Location, ScrollOffsetType.Current).Y = saveOffsetY + (float)(anchorZ - top.Z);
-        side.ScrollData!.Offset(wall.Location, ScrollOffsetType.Previous).Y = saveOffsetY + (float)(prevAnchorZ - top.PrevZ);
+        side.ScrollData!.Offset(wall.Location, ScrollOffsetType.Current).Y = saveOffsetY + (float)(anchorZ - top.Z + addOffsetZ);
+        side.ScrollData!.Offset(wall.Location, ScrollOffsetType.Previous).Y = saveOffsetY + (float)(prevAnchorZ - top.PrevZ + prevAddOffsetZ);
     }
 
     private static void AddVertices(DynamicArray<DynamicVertex> vertices, Span<DynamicVertex> add)

README.adoc

@@ -57,6 +57,6 @@ link:/ACS.md[ACS Support]
 
 ## Contact Us
 
-If you want to talk about the game, follow development, or get involved, we have https://discord.gg/sb8P7Nuby8[a Discord server] as well as https://www.doomworld.com/forum/topic/132153-helion-c-0940-824-goodbye-bsp-tree-rendering/[a thread on the Doomworld forums].
+If you want to talk about the game, follow development, or get involved, we have https://discord.gg/uCpmHdqnRc[a Discord server] as well as https://www.doomworld.com/forum/topic/132153-helion-c-0940-824-goodbye-bsp-tree-rendering/[a thread on the Doomworld forums].
 
 If you encounter issues using Helion and would like to report a bug, you can do so either https://github.com/Helion-Engine/Helion/issues[here on GitHub Issues] or in the Doomworld thread above.

Tests/Unit/GameAction/3DSector/Sector3D_Walls.cs

@@ -87,6 +87,25 @@ public void RenderLowerSliceWithNonSolidSector3D()
         result.Vertices.Length.Should().Be(12);
     }
 
+    [Fact(DisplayName = "Render correct offset when 3D sector line is covered by upper texture")]
+    public void RenderSectorLine3DWithUpper()
+    {
+        var sector = GameActions.GetSector(World, 240);
+        sector.Sectors3D.Length.Should().Be(1);
+        var sector3D = sector.Sectors3D[0];
+
+        SetSlices(new WallSlice(128, 80, 192, (0, 32)), new WallSlice(80, 64, 192, (0, 80)), new WallSlice(64, 32, 192, (0, 96)));
+
+        var line = GameActions.GetLine(World, 889);
+        GeometryRenderer.SetTestRenderSectorSliceFunc3D(RenderSlice3D);
+        var lineIndex = sector.Lines.IndexOf(line);
+        lineIndex.Should().NotBe(-1);
+        GeometryRenderer.SetSectorForLineRendering3D(sector3D);
+        GeometryRenderer.RenderSectorLine3D(sector3D, lineIndex, true, true, EmptyRenderSectorWallVertices3D);
+        GeometryRenderer.RestoreSectorSliceFunc3D();
+        AssertSlices();
+    }
+
     [Fact(DisplayName = "Render one-sided middle sector line sliced by single 3D sector with lower unpeg")]
     public void RenderOneSidedMiddleSliceLowerUnpeg()
     {