Use a different visibility buffer for each MTLCommandBuffer in a queue submit.

Docs/Whats_New.md

@@ -31,6 +31,7 @@ Released TBA
 - Detect when size of surface has changed under the covers.
 - Change rounding of surface size provided by Metal from truncation to rounding-with-half-to-even.
 - Queue submissions retain wait semaphores until `MTLCommandBuffer` finishes.
+- Use a different visibility buffer for each `MTLCommandBuffer` in a queue submit.
 - Work around problems with using explicit LoD with arrayed depth images on Apple Silicon.
 - Update `VK_MVK_MOLTENVK_SPEC_VERSION` to version `37`.
 

MoltenVK/MoltenVK/GPUObjects/MVKQueue.h

@@ -199,7 +199,10 @@ protected:
 #pragma mark -
 #pragma mark MVKQueueCommandBufferSubmission
 
-/** Submits the commands in a set of command buffers to the queue. */
+/**
+ * Submits an empty set of command buffers to the queue.
+ * Used for fence-only command submissions.
+ */
 class MVKQueueCommandBufferSubmission : public MVKQueueSubmission {
 
 public:
@@ -218,6 +221,7 @@ protected:
 	void finish() override;
 	virtual void submitCommandBuffers() {}
 
+	MVKCommandEncodingContext _encodingContext;
 	MVKSmallVector<std::pair<MVKSemaphore*, uint64_t>> _signalSemaphores;
 	MVKFence* _fence;
 	id<MTLCommandBuffer> _activeMTLCommandBuffer;

MoltenVK/MoltenVK/GPUObjects/MVKQueue.mm

@@ -367,12 +367,17 @@ void MVKQueueCommandBufferSubmission::commitActiveMTLCommandBuffer(bool signalCo
 	// Another option to wait on emulated semaphores once is to do it in the execute function, but doing it here
 	// should be more performant when prefilled command buffers aren't used, because we spend time encoding commands
 	// first, thus giving the command buffer signalling these semaphores more time to complete.
-	if (!_emulatedWaitDone)
-	{
+	if ( !_emulatedWaitDone ) {
 		for (auto& ws : _waitSemaphores) { ws.first->encodeWait(nil, ws.second); }
 		_emulatedWaitDone = true;
 	}
 
+	// The visibility result buffer will be returned to its pool when the active MTLCommandBuffer
+	// finishes executing, and therefore cannot be used beyond the active MTLCommandBuffer.
+	// By now, it's been submitted to the MTLCommandBuffer, so remove it from the encoding context,
+	// to ensure a fresh one will be used by commands executing on any subsequent MTLCommandBuffers.
+	_encodingContext.visibilityResultBuffer = nullptr;
+
 	// If we need to signal completion, use getActiveMTLCommandBuffer() to ensure at least
 	// one MTLCommandBuffer is used, otherwise if this instance has no content, it will not
 	// finish(), signal the fence and semaphores ,and be destroyed.
@@ -520,8 +525,7 @@ MVKQueueCommandBufferSubmission::~MVKQueueCommandBufferSubmission() {
 template <size_t N>
 void MVKQueueFullCommandBufferSubmission<N>::submitCommandBuffers() {
 	_queue->getPhysicalDevice()->startTimestampCorrelation(_cpuStart, _gpuStart);
-	MVKCommandEncodingContext encodingContext;
-	for (auto& cb : _cmdBuffers) { cb->submit(this, &encodingContext); }
+	for (auto& cb : _cmdBuffers) { cb->submit(this, &_encodingContext); }
 }
 
 template <size_t N>