From 4f101d98be95071d39433dfe11ca9707df74e8c5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Branimir=20Karad=C5=BEi=C4=87?= <branimirkaradzic@gmail.com>
Date: Fri, 19 Jun 2026 12:39:42 -0700
Subject: [PATCH] Don't present BGFX_FRAME_FLUSH frames. Fixed D3D12/VK flush
 sync. (#3771)

---
 src/bgfx.cpp           |  4 +++-
 src/bgfx_p.h           |  2 ++
 src/renderer_d3d12.cpp |  1 +
 src/renderer_vk.cpp    | 18 +++++++++++++-----
 src/renderer_vk.h      |  1 +
 5 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/src/bgfx.cpp b/src/bgfx.cpp
index dc45a4874..93e9606aa 100644
--- a/src/bgfx.cpp
+++ b/src/bgfx.cpp
@@ -2778,7 +2778,7 @@ namespace bgfx
 
 		if (!m_flipAfterRender)
 		{
-			if (!m_render->m_flush)
+			if (!m_flushPrevFrame)
 			{
 				BGFX_PROFILER_SCOPE("bgfx/flip", kColorSubmit);
 				flip();
@@ -2825,6 +2825,8 @@ namespace bgfx
 					flip();
 				}
 			}
+
+			m_flushPrevFrame = m_render->m_flush;
 		}
 		else
 		{
diff --git a/src/bgfx_p.h b/src/bgfx_p.h
index 03b6ae3e1..4fe7413ce 100644
--- a/src/bgfx_p.h
+++ b/src/bgfx_p.h
@@ -3928,6 +3928,7 @@ namespace bgfx
 			, m_exit(false)
 			, m_flipAfterRender(false)
 			, m_singleThreaded(false)
+			, m_flushPrevFrame(false)
 		{
 		}
 
@@ -6209,6 +6210,7 @@ namespace bgfx
 		bool m_flipAfterRender;
 		bool m_singleThreaded;
 		bool m_flipped;
+		bool m_flushPrevFrame;
 
 		typedef UpdateBatchT<256> TextureUpdateBatch;
 		BX_ALIGN_DECL_CACHE_LINE(TextureUpdateBatch m_textureUpdateBatch);
diff --git a/src/renderer_d3d12.cpp b/src/renderer_d3d12.cpp
index 763e1f115..4de3c50cb 100644
--- a/src/renderer_d3d12.cpp
+++ b/src/renderer_d3d12.cpp
@@ -7248,6 +7248,7 @@ namespace bgfx { namespace d3d12
 
 		D3D12_GPU_DESCRIPTOR_HANDLE gpuHandle;
 		ScratchBufferD3D12& scratchBuffer = m_scratchBuffer[m_backBufferColorIdx];
+		m_cmd.finish(m_backBufferColorFence[m_backBufferColorIdx]);
 		scratchBuffer.reset(gpuHandle);
 
 		m_uniformScratchBuffer.begin();
diff --git a/src/renderer_vk.cpp b/src/renderer_vk.cpp
index 0353b6f70..3b9129873 100644
--- a/src/renderer_vk.cpp
+++ b/src/renderer_vk.cpp
@@ -8384,6 +8384,9 @@ VK_DESTROY
 			m_lastImageRenderedSemaphore = m_renderDoneSemaphore[m_backBufferColorIdx];
 
 			m_needPresent = true;
+
+			s_renderVK->m_cmd.addWaitSemaphore(m_lastImageAcquiredSemaphore, VK_PIPELINE_STAGE_ALL_COMMANDS_BIT);
+			m_lastImageAcquiredSemaphore = VK_NULL_HANDLE;
 		}
 
 		return true;
@@ -8903,15 +8906,20 @@ VK_DESTROY
 		return result;
 	}
 
+	void CommandQueueVK::addWaitSemaphore(VkSemaphore _semaphore, VkPipelineStageFlags _waitStage)
+	{
+		BX_ASSERT(m_numWaitSemaphores < BX_COUNTOF(m_waitSemaphores), "Too many wait semaphores.");
+
+		m_waitSemaphores[m_numWaitSemaphores]      = _semaphore;
+		m_waitSemaphoreStages[m_numWaitSemaphores] = _waitStage;
+		m_numWaitSemaphores++;
+	}
+
 	void CommandQueueVK::addSwapChain(SwapChainVK& _swapChain)
 	{
 		if (VK_NULL_HANDLE != _swapChain.m_lastImageAcquiredSemaphore)
 		{
-			BX_ASSERT(m_numWaitSemaphores < BX_COUNTOF(m_waitSemaphores), "Too many wait semaphores.");
-
-			m_waitSemaphores[m_numWaitSemaphores]      = _swapChain.m_lastImageAcquiredSemaphore;
-			m_waitSemaphoreStages[m_numWaitSemaphores] = VK_PIPELINE_STAGE_ALL_COMMANDS_BIT;
-			m_numWaitSemaphores++;
+			addWaitSemaphore(_swapChain.m_lastImageAcquiredSemaphore, VK_PIPELINE_STAGE_ALL_COMMANDS_BIT);
 
 			_swapChain.m_lastImageAcquiredSemaphore = VK_NULL_HANDLE;
 		}
diff --git a/src/renderer_vk.h b/src/renderer_vk.h
index 646e75a65..0a0e80c44 100644
--- a/src/renderer_vk.h
+++ b/src/renderer_vk.h
@@ -912,6 +912,7 @@ VK_DESTROY_FUNC(DescriptorSet);
 		void shutdown();
 
 		VkResult alloc(VkCommandBuffer* _outCommandBuffer);
+		void addWaitSemaphore(VkSemaphore _semaphore, VkPipelineStageFlags _waitStage);
 		void addSwapChain(SwapChainVK& _swapChain);
 		void kick(bool _wait = false);
 		void finish(bool _finishAll = false);