Comment call to vkCreateInstance with a potential pitfall (#2642)

Although we could in principle write this explanatory message to stderr, that
would entangle this call with the layer search above for what is probably a
very unlikely possibility on any normal system.

1 files changed, 7 insertions, 1 deletions

diff --git a/tools/gfx/vulkan/vk-device.cpp b/tools/gfx/vulkan/vk-device.cpp
index 866b53d23..b5eec0b72 100644
--- a/tools/gfx/vulkan/vk-device.cpp
+++ b/tools/gfx/vulkan/vk-device.cpp
@@ -221,7 +221,13 @@ Result DeviceImpl::initVulkanInstanceAndDevice(
         for (auto apiVersion : apiVersionsToTry)
         {
             applicationInfo.apiVersion = apiVersion;
-            if (m_api.vkCreateInstance(&instanceCreateInfo, nullptr, &instance) == VK_SUCCESS)
+            // If r is VK_ERROR_LAYER_NOT_PRESENT, it's almost certainly
+            // because the layer shared library failed to load (we check that
+            // the layer is known earlier). It might, for example, be absent
+            // from the system library search path, and not referenced with an
+            // absolute path in VkLayer_khronos_validation.json.
+            const auto r = m_api.vkCreateInstance(&instanceCreateInfo, nullptr, &instance) ;
+            if (r == VK_SUCCESS)
             {
                 break;
             }