From c7363b6165a7795d10a8989c241dcdec84d0c7d7 Mon Sep 17 00:00:00 2001
From: Nicolas James <nj3ahxac@gmail.com>
Date: Thu, 15 Jan 2026 18:58:37 +1100
Subject: Add implementation of renderdoc's vulkan layer tutorial

---
 src/layer.cc | 408 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/layer.hh |  22 ++++
 2 files changed, 430 insertions(+)
 create mode 100644 src/layer.cc
 create mode 100644 src/layer.hh

(limited to 'src')

diff --git a/src/layer.cc b/src/layer.cc
new file mode 100644
index 0000000..24cc519
--- /dev/null
+++ b/src/layer.cc
@@ -0,0 +1,408 @@
+#include "layer.hh"
+
+#include <vulkan/utility/vk_dispatch_table.h>
+#include <vulkan/vk_layer.h>
+#include <vulkan/vk_platform.h>
+#include <vulkan/vulkan.h>
+#include <vulkan/vulkan.hpp>
+#include <vulkan/vulkan_core.h>
+
+#include <cstring>
+#include <iostream>
+#include <mutex>
+#include <string_view>
+#include <unordered_map>
+
+namespace low_latency {
+
+static auto mutex = std::mutex{};
+
+struct command_stats {
+    std::uint32_t num_draws;
+    std::uint32_t num_instances;
+    std::uint32_t num_verts;
+};
+static std::unordered_map<VkCommandBuffer, command_stats>
+    commandbuffer_to_stats{};
+static std::unordered_map<void*, VkuInstanceDispatchTable> instance_dispatch;
+static std::unordered_map<void*, VkuDeviceDispatchTable> device_dispatch;
+
+template <typename T>
+concept DispatchableType =
+    std::same_as<std::remove_cvref_t<T>, VkQueue> ||
+    std::same_as<std::remove_cvref_t<T>, VkCommandBuffer> ||
+    std::same_as<std::remove_cvref_t<T>, VkInstance> ||
+    std::same_as<std::remove_cvref_t<T>, VkDevice> ||
+    std::same_as<std::remove_cvref_t<T>, VkPhysicalDevice>;
+template <DispatchableType T> void* get_key(const T& inst) {
+    return *reinterpret_cast<void**>(inst);
+}
+
+static VKAPI_ATTR VkResult VKAPI_CALL
+BeginCommandBuffer(VkCommandBuffer command_buffer,
+                   const VkCommandBufferBeginInfo* begin_info) {
+    const auto lock = std::scoped_lock{mutex};
+    commandbuffer_to_stats[command_buffer] = {};
+    return device_dispatch[get_key(command_buffer)].BeginCommandBuffer(
+        command_buffer, begin_info);
+}
+
+static VKAPI_ATTR void VKAPI_CALL CmdDraw(VkCommandBuffer command_buffer,
+                                          std::uint32_t vertex_count,
+                                          std::uint32_t instance_count,
+                                          std::uint32_t first_vertex,
+                                          std::uint32_t first_instance) {
+
+    const auto lock = std::scoped_lock{mutex};
+
+    if (const auto it = commandbuffer_to_stats.find(command_buffer);
+        it != std::end(commandbuffer_to_stats)) {
+
+        auto& stats = it->second;
+        stats.num_draws++;
+        stats.num_instances += instance_count;
+        stats.num_verts += instance_count * vertex_count;
+    }
+
+    device_dispatch[get_key(command_buffer)].CmdDraw(
+        command_buffer, vertex_count, instance_count, first_vertex,
+        first_instance);
+}
+
+static VKAPI_ATTR void VKAPI_CALL CmdDrawIndexed(VkCommandBuffer command_buffer,
+                                                 uint32_t index_count,
+                                                 uint32_t instance_count,
+                                                 uint32_t first_index,
+                                                 int32_t vertex_offset,
+                                                 uint32_t first_instance) {
+
+    const auto lock = std::scoped_lock{mutex};
+
+    if (const auto it = commandbuffer_to_stats.find(command_buffer);
+        it != std::end(commandbuffer_to_stats)) {
+
+        auto& stats = it->second;
+        stats.num_draws++;
+        stats.num_instances += instance_count;
+        stats.num_verts += instance_count * index_count;
+    }
+
+    device_dispatch[get_key(command_buffer)].CmdDrawIndexed(
+        command_buffer, index_count, instance_count, first_index, vertex_offset,
+        first_instance);
+}
+
+static VKAPI_ATTR VkResult VKAPI_CALL
+EndCommandBuffer(VkCommandBuffer command_buffer) {
+
+    const auto lock = std::scoped_lock{mutex};
+
+    const auto& s = commandbuffer_to_stats[command_buffer];
+
+    std::cout << std::format("Command buffer ended with {} draws, {} "
+                             "instances and {} vertices\n",
+                             s.num_draws, s.num_instances, s.num_verts);
+
+    const auto it = device_dispatch.find(get_key(command_buffer));
+    if (it == std::end(device_dispatch)) {
+        return VK_ERROR_DEVICE_LOST;
+    }
+    return it->second.EndCommandBuffer(command_buffer);
+}
+
+static VKAPI_ATTR VkResult VKAPI_CALL
+CreateInstance(const VkInstanceCreateInfo* pCreateInfo,
+               const VkAllocationCallbacks* pAllocator, VkInstance* pInstance) {
+
+    // Iterate through list starting at pNext until we see create_info and
+    // link_info.
+    auto layer_create_info = [&]() -> VkLayerInstanceCreateInfo* {
+        for (auto base =
+                 reinterpret_cast<const VkBaseInStructure*>(pCreateInfo->pNext);
+             base; base = base->pNext) {
+
+            if (base->sType != VK_STRUCTURE_TYPE_LOADER_INSTANCE_CREATE_INFO) {
+                continue;
+            }
+
+            const auto info =
+                reinterpret_cast<const VkLayerInstanceCreateInfo*>(base);
+            if (info->function != VK_LAYER_LINK_INFO) {
+                continue;
+            }
+            return const_cast<VkLayerInstanceCreateInfo*>(info);
+        }
+        return nullptr;
+    }();
+
+    if (!layer_create_info || !layer_create_info->u.pLayerInfo) {
+        return VK_ERROR_INITIALIZATION_FAILED;
+    }
+
+    // Store our get instance proc addr function and pop it off our list +
+    // advance the list so future layers know what to call.
+    const auto next_gipa =
+        layer_create_info->u.pLayerInfo->pfnNextGetInstanceProcAddr;
+    if (!next_gipa) {
+        return VK_ERROR_INITIALIZATION_FAILED;
+    }
+    layer_create_info->u.pLayerInfo = layer_create_info->u.pLayerInfo->pNext;
+
+    // Call our create instance func, and store vkDestroyInstance, and
+    // vkCreateDevice as well.
+    const auto create_instance_func = reinterpret_cast<PFN_vkCreateInstance>(
+        next_gipa(VK_NULL_HANDLE, "vkCreateInstance"));
+    if (!create_instance_func) {
+        return VK_ERROR_INITIALIZATION_FAILED;
+    }
+
+    if (const auto result =
+            create_instance_func(pCreateInfo, pAllocator, pInstance);
+        result != VK_SUCCESS) {
+
+        return result;
+    }
+
+    const auto lock = std::scoped_lock{mutex};
+    instance_dispatch.emplace(
+        get_key(*pInstance),
+        VkuInstanceDispatchTable{
+            .DestroyInstance = reinterpret_cast<PFN_vkDestroyInstance>(
+                next_gipa(*pInstance, "vkDestroyInstance")),
+            .GetInstanceProcAddr = reinterpret_cast<PFN_vkGetInstanceProcAddr>(
+                next_gipa(*pInstance, "vkGetInstanceProcAddr")),
+            .EnumerateDeviceExtensionProperties =
+                reinterpret_cast<PFN_vkEnumerateDeviceExtensionProperties>(
+                    next_gipa(*pInstance,
+                              "vkEnumerateDeviceExtensionProperties")),
+        }
+
+    );
+
+    return VK_SUCCESS;
+}
+
+static VKAPI_ATTR void VKAPI_CALL
+DestroyInstance(VkInstance instance, const VkAllocationCallbacks* allocator) {
+
+    const auto lock = std::scoped_lock{mutex};
+    instance_dispatch.erase(get_key(instance));
+}
+
+static VKAPI_ATTR VkResult VKAPI_CALL CreateDevice(
+    VkPhysicalDevice physical_device, const VkDeviceCreateInfo* pCreateInfo,
+    const VkAllocationCallbacks* pAllocator, VkDevice* pDevice) {
+
+    auto layer_create_info = [&]() -> VkLayerDeviceCreateInfo* {
+        for (auto base =
+                 reinterpret_cast<const VkBaseInStructure*>(pCreateInfo->pNext);
+             base; base = base->pNext) {
+
+            if (base->sType != VK_STRUCTURE_TYPE_LOADER_DEVICE_CREATE_INFO) {
+                continue;
+            }
+
+            const auto info =
+                reinterpret_cast<const VkLayerDeviceCreateInfo*>(base);
+
+            if (info->function != VK_LAYER_LINK_INFO) {
+                continue;
+            }
+
+            return const_cast<VkLayerDeviceCreateInfo*>(info);
+        }
+        return nullptr;
+    }();
+
+    if (!layer_create_info || !layer_create_info->u.pLayerInfo) {
+        return VK_ERROR_INITIALIZATION_FAILED;
+    }
+
+    const auto next_gipa =
+        layer_create_info->u.pLayerInfo->pfnNextGetInstanceProcAddr;
+    const auto next_gdpa =
+        layer_create_info->u.pLayerInfo->pfnNextGetDeviceProcAddr;
+    if (!next_gipa || !next_gdpa) {
+        return VK_ERROR_INITIALIZATION_FAILED;
+    }
+    layer_create_info->u.pLayerInfo = layer_create_info->u.pLayerInfo->pNext;
+
+    const auto create_func = reinterpret_cast<PFN_vkCreateDevice>(
+        next_gipa(VK_NULL_HANDLE, "vkCreateDevice"));
+    if (!create_func) {
+        return VK_ERROR_INITIALIZATION_FAILED;
+    }
+
+    if (const auto result =
+            create_func(physical_device, pCreateInfo, pAllocator, pDevice);
+        result != VK_SUCCESS) {
+        return result;
+    }
+
+    const auto lock = std::scoped_lock{mutex};
+    device_dispatch.emplace(
+        get_key(*pDevice),
+        VkuDeviceDispatchTable{
+            .GetDeviceProcAddr = reinterpret_cast<PFN_vkGetDeviceProcAddr>(
+                next_gdpa(*pDevice, "vkGetDeviceProcAddr")),
+            .DestroyDevice = reinterpret_cast<PFN_vkDestroyDevice>(
+                next_gdpa(*pDevice, "vkDestroyDevice")),
+            .BeginCommandBuffer = reinterpret_cast<PFN_vkBeginCommandBuffer>(
+                next_gdpa(*pDevice, "vkBeginCommandBuffer")),
+            .EndCommandBuffer = reinterpret_cast<PFN_vkEndCommandBuffer>(
+                next_gdpa(*pDevice, "vkEndCommandBuffer")),
+            .CmdDraw = reinterpret_cast<PFN_vkCmdDraw>(
+                next_gdpa(*pDevice, "vkCmdDraw")),
+            .CmdDrawIndexed = reinterpret_cast<PFN_vkCmdDrawIndexed>(
+                next_gdpa(*pDevice, "vkCmdDrawIndexed")),
+        });
+
+    return VK_SUCCESS;
+}
+
+static VKAPI_ATTR void VKAPI_CALL
+DestroyDevice(VkDevice device, const VkAllocationCallbacks* allocator) {
+
+    const auto lock = std::scoped_lock{mutex};
+    device_dispatch.erase(get_key(device));
+}
+
+// These are wrong, the tutorial isn't correct afaik.
+static VKAPI_ATTR VkResult VKAPI_CALL EnumerateInstanceLayerProperties(
+    std::uint32_t* pPropertyCount, VkLayerProperties* pProperties) {
+
+    if (pPropertyCount) {
+        *pPropertyCount = 1;
+    }
+
+    if (pProperties) {
+        std::strcpy(pProperties->layerName, LAYER_NAME);
+        std::strcpy(pProperties->description, "Low Latency Layer");
+        pProperties->implementationVersion = 1;
+        pProperties->specVersion = VK_API_VERSION_1_3;
+    }
+
+    return VK_SUCCESS;
+}
+
+static VKAPI_ATTR VkResult VKAPI_CALL EnumerateDeviceLayerProperties(
+    VkPhysicalDevice physical_device, uint32_t* pPropertyCount,
+    VkLayerProperties* pProperties) {
+
+    return EnumerateInstanceLayerProperties(pPropertyCount, pProperties);
+}
+
+static VKAPI_ATTR VkResult VKAPI_CALL EnumerateInstanceExtensionProperties(
+    const char* pLayerName, uint32_t* pPropertyCount,
+    VkExtensionProperties* pProperties) {
+
+    if (!pLayerName || std::string_view{pLayerName} != LAYER_NAME) {
+
+        return VK_ERROR_LAYER_NOT_PRESENT;
+    }
+
+    if (pPropertyCount) {
+        *pPropertyCount = 0;
+    }
+    return VK_SUCCESS;
+}
+
+static VKAPI_ATTR VkResult VKAPI_CALL EnumerateDeviceExtensionProperties(
+    VkPhysicalDevice physical_device, const char* pLayerName,
+    uint32_t* pPropertyCount, VkExtensionProperties* pProperties) {
+
+    if (!pLayerName || std::string_view{pLayerName} != LAYER_NAME) {
+
+        if (physical_device == VK_NULL_HANDLE) {
+            return VK_SUCCESS;
+        }
+
+        const auto lock = std::scoped_lock{mutex};
+        return instance_dispatch[get_key(physical_device)]
+            .EnumerateDeviceExtensionProperties(physical_device, pLayerName,
+                                                pPropertyCount, pProperties);
+    }
+
+    if (pPropertyCount) {
+        *pPropertyCount = 0;
+    }
+    return VK_SUCCESS;
+}
+
+} // namespace low_latency
+
+static const auto instance_functions =
+    std::unordered_map<std::string_view, const PFN_vkVoidFunction>{
+        {"vkGetInstanceProcAddr",
+         reinterpret_cast<PFN_vkVoidFunction>(LowLatency_GetInstanceProcAddr)},
+
+        {"vkEnumerateInstanceLayerProperties",
+         reinterpret_cast<PFN_vkVoidFunction>(
+             low_latency::EnumerateInstanceLayerProperties)},
+        {"vkEnumerateInstanceExtensionProperties",
+         reinterpret_cast<PFN_vkVoidFunction>(
+             low_latency::EnumerateInstanceExtensionProperties)},
+
+        {"vkCreateInstance",
+         reinterpret_cast<PFN_vkVoidFunction>(low_latency::CreateInstance)},
+        {"vkDestroyInstance",
+         reinterpret_cast<PFN_vkVoidFunction>(low_latency::DestroyInstance)},
+    };
+
+static const auto device_functions =
+    std::unordered_map<std::string_view, const PFN_vkVoidFunction>{
+        {"vkGetDeviceProcAddr",
+         reinterpret_cast<PFN_vkVoidFunction>(LowLatency_GetDeviceProcAddr)},
+
+        {"vkEnumerateDeviceLayerProperties",
+         reinterpret_cast<PFN_vkVoidFunction>(
+             low_latency::EnumerateDeviceLayerProperties)},
+        {"vkEnumerateDeviceExtensionProperties",
+         reinterpret_cast<PFN_vkVoidFunction>(
+             low_latency::EnumerateDeviceExtensionProperties)},
+
+        {"vkCreateDevice",
+         reinterpret_cast<PFN_vkVoidFunction>(low_latency::CreateDevice)},
+        {"vkDestroyDevice",
+         reinterpret_cast<PFN_vkVoidFunction>(low_latency::DestroyDevice)},
+
+        {"vkCmdDraw",
+         reinterpret_cast<PFN_vkVoidFunction>(low_latency::CmdDraw)},
+        {"vkCmdDrawIndexed",
+         reinterpret_cast<PFN_vkVoidFunction>(low_latency::CmdDrawIndexed)},
+
+        {"vkBeginCommandBuffer",
+         reinterpret_cast<PFN_vkVoidFunction>(low_latency::BeginCommandBuffer)},
+        {"vkEndCommandBuffer",
+         reinterpret_cast<PFN_vkVoidFunction>(low_latency::EndCommandBuffer)},
+    };
+
+VKAPI_ATTR PFN_vkVoidFunction VKAPI_CALL
+LowLatency_GetDeviceProcAddr(VkDevice device, const char* const pName) {
+
+    if (const auto it = device_functions.find(pName);
+        it != std::end(device_functions)) {
+
+        return it->second;
+    }
+
+    const auto lock = std::scoped_lock{low_latency::mutex};
+    return low_latency::device_dispatch[low_latency::get_key(device)]
+        .GetDeviceProcAddr(device, pName);
+}
+
+VKAPI_ATTR PFN_vkVoidFunction VKAPI_CALL
+LowLatency_GetInstanceProcAddr(VkInstance instance, const char* const pName) {
+
+    for (const auto& functions : {device_functions, instance_functions}) {
+        const auto it = functions.find(pName);
+        if (it == std::end(functions)) {
+            continue;
+        }
+        return it->second;
+    }
+
+    const auto lock = std::scoped_lock{low_latency::mutex};
+    return low_latency::instance_dispatch[low_latency::get_key(instance)]
+        .GetInstanceProcAddr(instance, pName);
+}
\ No newline at end of file
diff --git a/src/layer.hh b/src/layer.hh
new file mode 100644
index 0000000..5633c63
--- /dev/null
+++ b/src/layer.hh
@@ -0,0 +1,22 @@
+#ifndef LAYER_HH_
+#define LAYER_HH_
+
+#include <vulkan/vk_platform.h>
+#include <vulkan/vulkan.hpp>
+
+extern "C" {
+
+VKAPI_ATTR PFN_vkVoidFunction VKAPI_CALL
+LowLatency_GetInstanceProcAddr(VkInstance instance, const char* const pname);
+
+VKAPI_ATTR PFN_vkVoidFunction VKAPI_CALL
+LowLatency_GetDeviceProcAddr(VkDevice device, const char* pName);
+}
+
+namespace low_latency {
+
+static constexpr auto LAYER_NAME = "VK_LAYER_NJ3AHXAC_LowLatency";
+
+}
+
+#endif
\ No newline at end of file
-- 
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