fix #451: stabilize portal seam rendering

tests/AcDream.App.Tests/Rendering/ParticleBindlessInstanceTests.cs

@@ -14,11 +14,15 @@ public sealed class ParticleBindlessInstanceTests
         // one TextureIndex (a binding=9 handle-table slot, 4 bytes), so the
         // struct shrank by 4 bytes; TextureIndex keeps TextureHandleLow's
         // former offset (64 — right after the four vec4 fields).
-        Assert.Equal(68, Marshal.SizeOf<ParticleRenderer.BillboardGpuInstance>());
+        Assert.Equal(72, Marshal.SizeOf<ParticleRenderer.BillboardGpuInstance>());
         Assert.Equal(
             new IntPtr(64),
             Marshal.OffsetOf<ParticleRenderer.BillboardGpuInstance>(
                 nameof(ParticleRenderer.BillboardGpuInstance.TextureIndex)));
+        Assert.Equal(
+            new IntPtr(68),
+            Marshal.OffsetOf<ParticleRenderer.BillboardGpuInstance>(
+                nameof(ParticleRenderer.BillboardGpuInstance.ClipSlot)));
     }
 
     [Fact]
@@ -40,6 +44,8 @@ public sealed class ParticleBindlessInstanceTests
         // index rather than by a null handle, because Vulkan's descriptor array
         // cannot be asked whether an element was ever written.
         Assert.Contains("layout(location = 6) in uint aTextureIndex;", vertex);
+        Assert.Contains("layout(location = 7) in uint aClipSlot;", vertex);
+        Assert.Contains("clipRegions[aClipSlot]", vertex);
         Assert.Contains("flat out uint vTextureIndex;", vertex);
         Assert.Contains("vTextureIndex = aTextureIndex;", vertex);
         Assert.Contains("#extension GL_ARB_bindless_texture : require", fragment);