From 1d8f6d8ee94cced96cd10033592bc429609f14f7 Mon Sep 17 00:00:00 2001
From: Francis De Brabandere <francisdb@gmail.com>
Date: Wed, 17 Jun 2026 16:05:02 +0200
Subject: [PATCH] Vulkan: do not block acquiring window swap chain images
 (#3752)

Acquiring waited forever for an image on every swap chain from the one
submit thread, so a single swap chain that is no longer served (e.g. a
fully occluded window on a Wayland compositor without fifo-v1, which
stops releasing buffers) stalled rendering of all windows. Window swap
chains now acquire without blocking and are skipped for the frame when
no image is available; only the main back buffer may block, as that is
the frame pacing. Image availability acts as natural back pressure, no
compositor specific behavior is needed.
---
 src/renderer_vk.cpp | 22 +++++++++++++++++-----
 src/renderer_vk.h   |  4 ++--
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/src/renderer_vk.cpp b/src/renderer_vk.cpp
index ae58f8a76..29887ff37 100644
--- a/src/renderer_vk.cpp
+++ b/src/renderer_vk.cpp
@@ -3224,7 +3224,10 @@ VK_IMPORT_DEVICE
 			else
 			{
 				int64_t start = bx::getHPCounter();
-				newFrameBuffer.acquire(m_commandBuffer);
+				// Only block acquiring the main back buffer: window swap chains may not be
+				// served anymore (e.g. fully occluded window on Wayland compositors without
+				// fifo-v1) and must not stall the whole frame.
+				newFrameBuffer.acquire(m_commandBuffer, &newFrameBuffer == &m_backBuffer);
 				m_presentElapsed += bx::getHPCounter() - start;
 			}
 
@@ -8297,7 +8300,7 @@ VK_DESTROY
 		return idx;
 	}
 
-	bool SwapChainVK::acquire(VkCommandBuffer _commandBuffer)
+	bool SwapChainVK::acquire(VkCommandBuffer _commandBuffer, bool _block)
 	{
 		BGFX_PROFILER_SCOPE("SwapChainVK::acquire", kColorFrame);
 
@@ -8321,13 +8324,22 @@ VK_DESTROY
 				result = vkAcquireNextImageKHR(
 					  device
 					, m_swapChain
-					, UINT64_MAX
+					, _block ? UINT64_MAX : 0
 					, m_lastImageAcquiredSemaphore
 					, VK_NULL_HANDLE
 					, &m_backBufferColorIdx
 					);
 			}
 
+			if (!_block
+			&& (VK_NOT_READY == result || VK_TIMEOUT == result) )
+			{
+				// No image available without blocking, e.g. a fully occluded window the
+				// compositor stopped serving; skip this swap chain for this frame instead
+				// of stalling all swap chains. The semaphore was not used, undo the rotation.
+				m_currentSemaphore = (m_currentSemaphore + kMaxBackBuffers - 1) % kMaxBackBuffers;
+				return false;
+			}
 
 			if (result != VK_SUCCESS)
 			{
@@ -8686,7 +8698,7 @@ VK_DESTROY
 		return denseIdx;
 	}
 
-	bool FrameBufferVK::acquire(VkCommandBuffer _commandBuffer)
+	bool FrameBufferVK::acquire(VkCommandBuffer _commandBuffer, bool _block)
 	{
 		BX_ASSERT(NULL != m_nwh, "FrameBufferVK::acquire is only valid for swap-chain framebuffers.");
 		BGFX_PROFILER_SCOPE("FrameBufferVK::acquire", kColorFrame);
@@ -8704,7 +8716,7 @@ VK_DESTROY
 			_commandBuffer = s_renderVK->m_commandBuffer;
 		}
 
-		const bool acquired = m_swapChain.acquire(_commandBuffer);
+		const bool acquired = m_swapChain.acquire(_commandBuffer, _block);
 		m_needPresent = m_swapChain.m_needPresent;
 		m_currentFramebuffer = m_swapChain.m_backBufferFrameBuffer[m_swapChain.m_backBufferColorIdx];
 
diff --git a/src/renderer_vk.h b/src/renderer_vk.h
index 1b7a1bf9f..646e75a65 100644
--- a/src/renderer_vk.h
+++ b/src/renderer_vk.h
@@ -796,7 +796,7 @@ VK_DESTROY_FUNC(DescriptorSet);
 		uint32_t findPresentMode(bool _vsync);
 		TextureFormat::Enum findSurfaceFormat(TextureFormat::Enum _format, VkColorSpaceKHR _colorSpace, bool _srgb);
 
-		bool acquire(VkCommandBuffer _commandBuffer);
+		bool acquire(VkCommandBuffer _commandBuffer, bool _block = true);
 		void present();
 
 		void transitionImage(VkCommandBuffer _commandBuffer);
@@ -875,7 +875,7 @@ VK_DESTROY_FUNC(DescriptorSet);
 
 		void resolve();
 
-		bool acquire(VkCommandBuffer _commandBuffer);
+		bool acquire(VkCommandBuffer _commandBuffer, bool _block = true);
 		void present();
 
 		void markDirty() { m_needResolve = true; }