From f7f58ac60bf20c5f8053993d6298702af84816e6 Mon Sep 17 00:00:00 2001
From: xirreal <34745171+xirreal@users.noreply.github.com>
Date: Tue, 24 Feb 2026 11:00:35 +0100
Subject: [PATCH 1/2] Round capacity estimates to multiples of 4 to make sure
 allocations are always aligned

---
 .../caffeinemc/mods/sodium/client/gl/arena/GlBufferArena.java   | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/common/src/main/java/net/caffeinemc/mods/sodium/client/gl/arena/GlBufferArena.java b/common/src/main/java/net/caffeinemc/mods/sodium/client/gl/arena/GlBufferArena.java
index 9e38fd2f60..243a8578f7 100644
--- a/common/src/main/java/net/caffeinemc/mods/sodium/client/gl/arena/GlBufferArena.java
+++ b/common/src/main/java/net/caffeinemc/mods/sodium/client/gl/arena/GlBufferArena.java
@@ -379,7 +379,7 @@ private long estimateNewCapacity(float regionFillFractionInv, List<PendingUpload
         } else {
             newCapacity = (long) (requiredTotalSize * FEW_SEGMENTS_GROWTH_FACTOR);
         }
-        return newCapacity;
+        return (newCapacity + 3) & ~3;
     }
 
     private long getRequiredTotalSize(List<PendingUpload> queue) {

From 3fcdc00a168846ae340785c687dcd6cf364098a5 Mon Sep 17 00:00:00 2001
From: xirreal <34745171+xirreal@users.noreply.github.com>
Date: Thu, 26 Feb 2026 10:19:31 +0100
Subject: [PATCH 2/2] Add explaination for rounding of new capacity estimate

---
 .../mods/sodium/client/gl/arena/GlBufferArena.java       | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/common/src/main/java/net/caffeinemc/mods/sodium/client/gl/arena/GlBufferArena.java b/common/src/main/java/net/caffeinemc/mods/sodium/client/gl/arena/GlBufferArena.java
index 243a8578f7..2b5df04128 100644
--- a/common/src/main/java/net/caffeinemc/mods/sodium/client/gl/arena/GlBufferArena.java
+++ b/common/src/main/java/net/caffeinemc/mods/sodium/client/gl/arena/GlBufferArena.java
@@ -379,6 +379,15 @@ private long estimateNewCapacity(float regionFillFractionInv, List<PendingUpload
         } else {
             newCapacity = (long) (requiredTotalSize * FEW_SEGMENTS_GROWTH_FACTOR);
         }
+        // round up to the next multiple of 4
+        // since the new capacity is estimated using non-integers factors, it may end up not being a multiple of 4
+        // this causes three separate issues:
+        // 1. new segments are always allocated at the end of the free segment, but since the tail is calculated from the capacity,
+        //    segments may end up misaligned
+        // 2. terrain is rendered with glDrawElementsBaseCount, and since baseCount may not be even, gl_VertexID % 4 would
+        //    would not be reliable to detect quads as baseCount is added to the vertex ID
+        // 3. misaligned segments on NVIDIA GPUs seem to confuse the driver into splitting quads across workgroups,
+        //    possibly due to how the shared index buffer works
         return (newCapacity + 3) & ~3;
     }