From 924f01f5833b3b3921c2fe148e08f46519d13a07 Mon Sep 17 00:00:00 2001
From: CamilleLaVey <camillelavey99@gmail.com>
Date: Sat, 29 Nov 2025 18:20:54 -0400
Subject: [PATCH] [vk] BufferCache NullBuffer handling [POSSIBLE REVERT]

---
 .../renderer_vulkan/vk_buffer_cache.cpp       | 39 +++++++++++++++----
 .../renderer_vulkan/vk_buffer_cache.h         |  5 +++
 2 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/src/video_core/renderer_vulkan/vk_buffer_cache.cpp b/src/video_core/renderer_vulkan/vk_buffer_cache.cpp
index 1e974223c8..62983ac78f 100644
--- a/src/video_core/renderer_vulkan/vk_buffer_cache.cpp
+++ b/src/video_core/renderer_vulkan/vk_buffer_cache.cpp
@@ -664,22 +664,41 @@ void BufferCacheRuntime::ReserveNullBuffer() {
     }
 }
 
+VkBufferUsageFlags BufferCacheRuntime::NullBufferUsageFlags() const {
+    VkBufferUsageFlags usage = VK_BUFFER_USAGE_TRANSFER_SRC_BIT | VK_BUFFER_USAGE_TRANSFER_DST_BIT |
+                              VK_BUFFER_USAGE_UNIFORM_TEXEL_BUFFER_BIT |
+                              VK_BUFFER_USAGE_STORAGE_TEXEL_BUFFER_BIT |
+                              VK_BUFFER_USAGE_UNIFORM_BUFFER_BIT | VK_BUFFER_USAGE_STORAGE_BUFFER_BIT |
+                              VK_BUFFER_USAGE_VERTEX_BUFFER_BIT | VK_BUFFER_USAGE_INDEX_BUFFER_BIT |
+                              VK_BUFFER_USAGE_INDIRECT_BUFFER_BIT;
+    if (device.IsExtTransformFeedbackSupported()) {
+        usage |= VK_BUFFER_USAGE_TRANSFORM_FEEDBACK_BUFFER_BIT_EXT;
+    }
+    return usage;
+}
+
+void BufferCacheRuntime::RefreshNullBuffer() {
+    if (!null_buffer) {
+        return;
+    }
+    scheduler.Finish();
+    null_buffer.reset();
+    null_buffer = CreateNullBuffer();
+}
+
 vk::Buffer BufferCacheRuntime::CreateNullBuffer() {
     VkBufferCreateInfo create_info{
         .sType = VK_STRUCTURE_TYPE_BUFFER_CREATE_INFO,
         .pNext = nullptr,
         .flags = 0,
         .size = 4,
-        .usage = VK_BUFFER_USAGE_VERTEX_BUFFER_BIT | VK_BUFFER_USAGE_INDEX_BUFFER_BIT |
-                 VK_BUFFER_USAGE_TRANSFER_DST_BIT | VK_BUFFER_USAGE_INDIRECT_BUFFER_BIT,
+        .usage = NullBufferUsageFlags(),
         .sharingMode = VK_SHARING_MODE_EXCLUSIVE,
         .queueFamilyIndexCount = 0,
         .pQueueFamilyIndices = nullptr,
     };
-    if (device.IsExtTransformFeedbackSupported()) {
-        create_info.usage |= VK_BUFFER_USAGE_TRANSFORM_FEEDBACK_BUFFER_BIT_EXT;
-    }
     vk::Buffer ret = memory_allocator.CreateBuffer(create_info, MemoryUsage::DeviceLocal);
+    null_buffer_usage_flags = create_info.usage;
     if (device.HasDebuggingToolAttached()) {
         ret.SetObjectNameEXT("Null buffer");
     }
@@ -690,6 +709,10 @@ vk::Buffer BufferCacheRuntime::CreateNullBuffer() {
     });
 
     return ret;
-}
-
-} // namespace Vulkan
+        const VkBufferUsageFlags expected_usage = NullBufferUsageFlags();
+        if (null_buffer && null_buffer_usage_flags != expected_usage) {
+            RefreshNullBuffer();
+        }
+        if (!null_buffer) {
+            null_buffer = CreateNullBuffer();
+        }
diff --git a/src/video_core/renderer_vulkan/vk_buffer_cache.h b/src/video_core/renderer_vulkan/vk_buffer_cache.h
index d5d806fc69..66eb2bceb1 100644
--- a/src/video_core/renderer_vulkan/vk_buffer_cache.h
+++ b/src/video_core/renderer_vulkan/vk_buffer_cache.h
@@ -131,6 +131,9 @@ public:
 
     void BindTransformFeedbackBuffers(VideoCommon::HostBindings<Buffer>& bindings);
 
+    /// Forces destruction and recreation of the shared null buffer so new usage flags take effect.
+    void RefreshNullBuffer();
+
     std::span<u8> BindMappedUniformBuffer([[maybe_unused]] size_t stage,
                                           [[maybe_unused]] u32 binding_index,
                                           u32 size) {
@@ -168,6 +171,7 @@ private:
 
     void ReserveNullBuffer();
     vk::Buffer CreateNullBuffer();
+    VkBufferUsageFlags NullBufferUsageFlags() const;
 
     const Device& device;
     MemoryAllocator& memory_allocator;
@@ -179,6 +183,7 @@ private:
     std::shared_ptr<QuadStripIndexBuffer> quad_strip_index_buffer;
 
     vk::Buffer null_buffer;
+    VkBufferUsageFlags null_buffer_usage_flags = 0;
 
     std::unique_ptr<Uint8Pass> uint8_pass;
     QuadIndexedPass quad_index_pass;