Add the Vulkan loader as an optional dependency and use it on Mac

On macOS we can't rely on having the Vulkan loader installed in the
system. So we add the Vulkan loader as an optional dependency of Dawn
and use it on macOS when building Dawn in standalone with Vulkan
support.

Usage of building our own loader might broaden if the loader gains
features that are useful on other OSes. For example the ability to pass
in the "root ICD" entrypoint to the loader so we can have both
Swiftshader and the system driver at the same time.

Bug: dawn:388

Change-Id: I7ade4961cce0463c66846ad17aebf95224f1afcc
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/19723
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

.gitignore

@@ -23,6 +23,7 @@ third_party/swiftshader/
 third_party/spirv-cross/
 third_party/spirv-headers/
 third_party/vulkan-headers/
+third_party/vulkan-loader/
 third_party/vulkan-validation-layers/
 tools
 out

DEPS

@@ -101,17 +101,19 @@ deps = {
     'condition': 'dawn_standalone and checkout_linux',
   },
 
-  # Khronos Vulkan-Headers
+  # Khronos Vulkan headers, validation layers and loader.
   'third_party/vulkan-headers': {
     'url': '{chromium_git}/external/github.com/KhronosGroup/Vulkan-Headers@e01f13e1f777cf592ebd1a5f4836d4cd10ed85f6',
     'condition': 'dawn_standalone',
   },
-
-  # Khronos Vulkan-ValidationLayers
   'third_party/vulkan-validation-layers': {
     'url': '{chromium_git}/external/github.com/KhronosGroup/Vulkan-ValidationLayers@1533266eac486fae0c34bffe4868c4bc91dbe078',
     'condition': 'dawn_standalone',
   },
+  'third_party/vulkan-loader': {
+    'url': '{chromium_git}/external/github.com/KhronosGroup/Vulkan-Loader@3f7e3cbf33a732e945b3780212aad853ca0add29',
+    'condition': 'dawn_standalone',
+  },
 
   'third_party/swiftshader': {
     'url': '{swiftshader_git}/SwiftShader@63ed0e445fa525ee01637350ea92fbdaa2226c73',

build_overrides/dawn.gni

@@ -35,4 +35,5 @@ dawn_shaderc_dir = "//third_party/shaderc"
 dawn_spirv_tools_dir = "//third_party/SPIRV-Tools"
 dawn_spirv_cross_dir = "//third_party/spirv-cross"
 dawn_swiftshader_dir = "//third_party/swiftshader"
+dawn_vulkan_loader_dir = "//third_party/vulkan-loader"
 dawn_vulkan_validation_layers_dir = "//third_party/vulkan-validation-layers"

build_overrides/vulkan_loader.gni

@@ -0,0 +1,18 @@
+# Copyright 2020 The Dawn Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+vulkan_headers_dir = "//third_party/vulkan-headers"
+
+vulkan_gen_subdir = "vulkan_loader"
+vulkan_loader_shared = true

scripts/dawn_features.gni

@@ -74,9 +74,13 @@ declare_args() {
 # Put them in two separate declare_args() when setting the value of one
 # argument based on another.
 declare_args() {
-  # Uses our built version of Vulkan validation layers
+  # Uses our built version of the Vulkan validation layers
   dawn_enable_vulkan_validation_layers =
-      dawn_enable_vulkan && ((is_linux && !is_chromeos) || is_win)
+      dawn_enable_vulkan && ((is_linux && !is_chromeos) || is_win || is_mac)
+
+  # Uses our built version of the Vulkan loader on platforms where we can't
+  # assume to have one present at the system level.
+  dawn_enable_vulkan_loader = dawn_enable_vulkan && is_mac
 }
 
 dawn_supports_glfw_for_windowing =

scripts/dawn_overrides_with_defaults.gni

@@ -62,6 +62,11 @@ if (!defined(dawn_swiftshader_dir)) {
   dawn_swiftshader_dir = ""
 }
 
+if (!defined(dawn_vulkan_loader_dir)) {
+  # Default to the Vulkan loader not being available.
+  dawn_vulkan_loader_dir = ""
+}
+
 if (!defined(dawn_vulkan_validation_layers_dir)) {
   # Default to VVLs not being available.
   dawn_vulkan_validation_layers_dir = ""

src/dawn_native/BUILD.gn

@@ -28,22 +28,28 @@ if (is_mac) {
   }
 }
 
+# The VVLs are an optional dependency, only use it if the path has been set.
 enable_vulkan_validation_layers = dawn_enable_vulkan_validation_layers &&
                                   dawn_vulkan_validation_layers_dir != ""
 if (enable_vulkan_validation_layers) {
   import("//build_overrides/vulkan_validation_layers.gni")
 }
 
-# Swiftshader is an optional dependency of Dawn so we only use it if the path
-# to it has been set.
+# Swiftshader is an optional dependency, only use it if the path has been set.
 use_swiftshader = dawn_use_swiftshader && dawn_swiftshader_dir != ""
-
 if (use_swiftshader) {
   assert(dawn_enable_vulkan,
          "dawn_use_swiftshader requires dawn_enable_vulkan=true")
   import("${dawn_swiftshader_dir}/src/Vulkan/vulkan.gni")
 }
 
+# The Vulkan loader is an optional dependency, only use it if the path has been
+# set.
+if (dawn_enable_vulkan) {
+  enable_vulkan_loader =
+      dawn_enable_vulkan_loader && dawn_vulkan_loader_dir != ""
+}
+
 config("dawn_native_internal") {
   configs = [ "${dawn_root}/src/common:dawn_internal" ]
 
@@ -102,9 +108,7 @@ if (dawn_enable_opengl) {
 # Public dawn_native headers so they can be publicly visible for
 # dependencies of dawn_native
 source_set("dawn_native_headers") {
-  public_deps = [
-    "${dawn_root}/src/dawn:dawncpp_headers",
-  ]
+  public_deps = [ "${dawn_root}/src/dawn:dawncpp_headers" ]
   all_dependent_configs = [ "${dawn_root}/src/common:dawn_public_include_dirs" ]
   sources = [
     "${dawn_root}/src/include/dawn_native/DawnNative.h",
@@ -554,7 +558,9 @@ source_set("dawn_native_sources") {
         "DAWN_VK_DATA_DIR=\"$vulkan_data_subdir\"",
       ]
     }
-
+    if (enable_vulkan_loader) {
+      data_deps += [ "${dawn_vulkan_loader_dir}:libvulkan" ]
+    }
     if (use_swiftshader) {
       data_deps += [
         "${dawn_swiftshader_dir}/src/Vulkan:icd_file",
@@ -575,17 +581,13 @@ dawn_component("dawn_native") {
   DEFINE_PREFIX = "DAWN_NATIVE"
 
   #Make headers publically visible
-  public_deps = [
-    ":dawn_native_headers",
-  ]
+  public_deps = [ ":dawn_native_headers" ]
 
   deps = [
     ":dawn_native_sources",
     "${dawn_root}/src/common",
   ]
-  sources = [
-    "DawnNative.cpp",
-  ]
+  sources = [ "DawnNative.cpp" ]
   configs = [ ":dawn_native_internal" ]
   public_configs = [ ":dawn_native_weak_framework" ]
 
@@ -605,9 +607,8 @@ dawn_component("dawn_native") {
     sources += [ "vulkan/VulkanBackend.cpp" ]
 
     if (enable_vulkan_validation_layers) {
-      data_deps = [
-        "${dawn_vulkan_validation_layers_dir}:vulkan_validation_layers",
-      ]
+      data_deps =
+          [ "${dawn_vulkan_validation_layers_dir}:vulkan_validation_layers" ]
       if (!is_android) {
         data_deps +=
             [ "${dawn_vulkan_validation_layers_dir}:vulkan_gen_json_files" ]

src/dawn_native/vulkan/BackendVk.cpp

@@ -42,10 +42,10 @@ constexpr char kVulkanLibName[] = "libvulkan.so.1";
 #    endif
 #elif defined(DAWN_PLATFORM_WINDOWS)
 constexpr char kVulkanLibName[] = "vulkan-1.dll";
+#elif defined(DAWN_PLATFORM_MACOS)
+constexpr char kVulkanLibName[] = "libvulkan.dylib";
 #elif defined(DAWN_PLATFORM_FUCHSIA)
 constexpr char kVulkanLibName[] = "libvulkan.so";
-#elif defined(DAWN_ENABLE_SWIFTSHADER)
-const char* kVulkanLibName = kSwiftshaderLibName;
 #else
 #    error "Unimplemented Vulkan backend platform"
 #endif