From c5acacff672d8d8a3acd1ec63dcf41709d06246b Mon Sep 17 00:00:00 2001
From: Philip Rideout <philiprideout@gmail.com>
Date: Mon, 29 Jun 2020 11:06:27 -0700
Subject: [PATCH] Vulkan: add note about #1532.

---
 filament/backend/src/vulkan/VulkanContext.cpp | 15 ++++++++++++++-
 filament/backend/src/vulkan/VulkanContext.h   |  2 +-
 filament/backend/src/vulkan/VulkanDriver.cpp  |  2 +-
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/filament/backend/src/vulkan/VulkanContext.cpp b/filament/backend/src/vulkan/VulkanContext.cpp
index 433e6025ae..4a01f3a6c1 100644
--- a/filament/backend/src/vulkan/VulkanContext.cpp
+++ b/filament/backend/src/vulkan/VulkanContext.cpp
@@ -155,7 +155,7 @@ void selectPhysicalDevice(VulkanContext& context) {
     PANIC_POSTCONDITION("Unable to find suitable device.");
 }
 
-void createVirtualDevice(VulkanContext& context) {
+void createLogicalDevice(VulkanContext& context) {
     VkDeviceQueueCreateInfo deviceQueueCreateInfo[1] = {};
     const float queuePriority[] = {1.0f};
     VkDeviceCreateInfo deviceCreateInfo = {};
@@ -279,7 +279,20 @@ void getPresentationQueue(VulkanContext& context, VulkanSurfaceContext& sc) {
     ASSERT_POSTCONDITION(presentQueueFamilyIndex != 0xffff,
             "This physical device does not support the presentation queue.");
     if (context.graphicsQueueFamilyIndex != presentQueueFamilyIndex) {
+
+        // TODO: Strictly speaking, this code path is incorrect. However it is not triggered on any
+        // Android devices that we've tested with, nor with MoltenVK.
+        //
+        // This is incorrect because we created the logical device early on, before we had a handle
+        // to the rendering surface. Therefore the device was not created with the presentation
+        // queue family index included in VkDeviceQueueCreateInfo.
+        //
+        // This is non-trivial to fix because the driver API allows clients to do certain things
+        // (e.g. upload a vertex buffer) before the swap chain is created.
+        //
+        // https://github.com/google/filament/issues/1532
         vkGetDeviceQueue(context.device, presentQueueFamilyIndex, 0, &sc.presentQueue);
+
     } else {
         sc.presentQueue = context.graphicsQueue;
     }
diff --git a/filament/backend/src/vulkan/VulkanContext.h b/filament/backend/src/vulkan/VulkanContext.h
index 083ca82869..366e32218f 100644
--- a/filament/backend/src/vulkan/VulkanContext.h
+++ b/filament/backend/src/vulkan/VulkanContext.h
@@ -143,7 +143,7 @@ struct VulkanSurfaceContext {
 };
 
 void selectPhysicalDevice(VulkanContext& context);
-void createVirtualDevice(VulkanContext& context);
+void createLogicalDevice(VulkanContext& context);
 void getPresentationQueue(VulkanContext& context, VulkanSurfaceContext& sc);
 void getSurfaceCaps(VulkanContext& context, VulkanSurfaceContext& sc);
 
diff --git a/filament/backend/src/vulkan/VulkanDriver.cpp b/filament/backend/src/vulkan/VulkanDriver.cpp
index 95fdca6df8..8314c855ea 100644
--- a/filament/backend/src/vulkan/VulkanDriver.cpp
+++ b/filament/backend/src/vulkan/VulkanDriver.cpp
@@ -158,7 +158,7 @@ VulkanDriver::VulkanDriver(VulkanPlatform* platform,
     selectPhysicalDevice(mContext);
 
     // Initialize device and graphicsQueue.
-    createVirtualDevice(mContext);
+    createLogicalDevice(mContext);
     mBinder.setDevice(mContext.device);
 
     // Choose a depth format that meets our requirements. Take care not to include stencil formats