vk_buffer_cache: Use emulated null buffers for transform feedback

Vulkan does not support null buffers on transform feedback bindings.
Emulate these using the same null buffer we were using for index
buffers.

src/video_core/renderer_vulkan/vk_buffer_cache.cpp

@@ -152,8 +152,8 @@ void BufferCacheRuntime::BindIndexBuffer(PrimitiveTopology topology, IndexFormat
     }
     if (vk_buffer == VK_NULL_HANDLE) {
         // Vulkan doesn't support null index buffers. Replace it with our own null buffer.
-        ReserveNullIndexBuffer();
-        vk_buffer = *null_index_buffer;
+        ReserveNullBuffer();
+        vk_buffer = *null_buffer;
     }
     scheduler.Record([vk_buffer, vk_offset, vk_index_type](vk::CommandBuffer cmdbuf) {
         cmdbuf.BindIndexBuffer(vk_buffer, vk_offset, vk_index_type);
@@ -195,6 +195,14 @@ void BufferCacheRuntime::BindTransformFeedbackBuffer(u32 index, VkBuffer buffer,
         // Already logged in the rasterizer
         return;
     }
+    if (buffer == VK_NULL_HANDLE) {
+        // Vulkan doesn't support null transform feedback buffers.
+        // Replace it with our own null buffer.
+        ReserveNullBuffer();
+        buffer = *null_buffer;
+        offset = 0;
+        size = 0;
+    }
     scheduler.Record([index, buffer, offset, size](vk::CommandBuffer cmdbuf) {
         const VkDeviceSize vk_offset = offset;
         const VkDeviceSize vk_size = size;
@@ -279,11 +287,11 @@ void BufferCacheRuntime::ReserveQuadArrayLUT(u32 num_indices, bool wait_for_idle
     });
 }
 
-void BufferCacheRuntime::ReserveNullIndexBuffer() {
-    if (null_index_buffer) {
+void BufferCacheRuntime::ReserveNullBuffer() {
+    if (null_buffer) {
         return;
     }
-    null_index_buffer = device.GetLogical().CreateBuffer(VkBufferCreateInfo{
+    null_buffer = device.GetLogical().CreateBuffer(VkBufferCreateInfo{
         .sType = VK_STRUCTURE_TYPE_BUFFER_CREATE_INFO,
         .pNext = nullptr,
         .flags = 0,
@@ -294,12 +302,12 @@ void BufferCacheRuntime::ReserveNullIndexBuffer() {
         .pQueueFamilyIndices = nullptr,
     });
     if (device.HasDebuggingToolAttached()) {
-        null_index_buffer.SetObjectNameEXT("Null index buffer");
+        null_buffer.SetObjectNameEXT("Null index buffer");
     }
-    null_index_buffer_commit = memory_allocator.Commit(null_index_buffer, MemoryUsage::DeviceLocal);
+    null_buffer_commit = memory_allocator.Commit(null_buffer, MemoryUsage::DeviceLocal);
 
     scheduler.RequestOutsideRenderPassOperationContext();
-    scheduler.Record([buffer = *null_index_buffer](vk::CommandBuffer cmdbuf) {
+    scheduler.Record([buffer = *null_buffer](vk::CommandBuffer cmdbuf) {
         cmdbuf.FillBuffer(buffer, 0, VK_WHOLE_SIZE, 0);
     });
 }

src/video_core/renderer_vulkan/vk_buffer_cache.h

@@ -92,7 +92,7 @@ private:
 
     void ReserveQuadArrayLUT(u32 num_indices, bool wait_for_idle);
 
-    void ReserveNullIndexBuffer();
+    void ReserveNullBuffer();
 
     const Device& device;
     MemoryAllocator& memory_allocator;
@@ -105,8 +105,8 @@ private:
     VkIndexType quad_array_lut_index_type{};
     u32 current_num_indices = 0;
 
-    vk::Buffer null_index_buffer;
-    MemoryCommit null_index_buffer_commit;
+    vk::Buffer null_buffer;
+    MemoryCommit null_buffer_commit;
 
     Uint8Pass uint8_pass;
     QuadIndexedPass quad_index_pass;