[Impeller] Refactor impeller.gni

impeller.gni turned from a small include file with minor templates into
a giant 1000 line mess of unrelated templates over time.

Moves templates into their own "TU"s. Once this patch sticks, will
document all the templates and flags. No change in functionality in this
patch. Just moves templates around.

Author: chinmaygarde

ci/licenses_golden/excluded_files

@@ -201,10 +201,10 @@
 ../../../flutter/impeller/tessellator/tessellator_unittests.cc
 ../../../flutter/impeller/toolkit/android/README.md
 ../../../flutter/impeller/toolkit/android/toolkit_android_unittests.cc
-../../../flutter/impeller/tools/build_metal_library.py
 ../../../flutter/impeller/tools/check_licenses.py
 ../../../flutter/impeller/tools/malioc_cores.py
 ../../../flutter/impeller/tools/malioc_diff.py
+../../../flutter/impeller/tools/metal_library.py
 ../../../flutter/impeller/tools/xxd.py
 ../../../flutter/impeller/typographer/typographer_unittests.cc
 ../../../flutter/lib/gpu/analysis_options.yaml

impeller/tools/args.gni

@@ -0,0 +1,62 @@
+# Copyright 2013 The Flutter Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//flutter/common/config.gni")
+import("//flutter/testing/testing.gni")
+
+declare_args() {
+  impeller_debug =
+      flutter_runtime_mode == "debug" || flutter_runtime_mode == "profile"
+
+  # Whether the runtime capture/playback system is enabled.
+  impeller_capture = flutter_runtime_mode == "debug"
+
+  # Whether the Metal backend is enabled.
+  impeller_enable_metal = (is_mac || is_ios) && target_os != "fuchsia"
+
+  # Whether the OpenGLES backend is enabled.
+  impeller_enable_opengles = (is_linux || is_win || is_android || is_mac ||
+                              enable_unittests) && target_os != "fuchsia"
+
+  # Whether the Vulkan backend is enabled.
+  impeller_enable_vulkan = (is_linux || is_win || is_android || is_mac ||
+                            enable_unittests) && target_os != "fuchsia"
+
+  # Whether to use a prebuilt impellerc.
+  # If this is the empty string, impellerc will be built.
+  # If it is non-empty, it should be the absolute path to impellerc.
+  impeller_use_prebuilt_impellerc = ""
+
+  # Whether to use a prebuilt scenec.
+  # If this is the empty string, scenec will be built.
+  # If it is non-empty, it should be the absolute path to scenec.
+  impeller_use_prebuilt_scenec = ""
+
+  # If enabled, all OpenGL calls will be traced. Because additional trace
+  # overhead may be substantial, this is not enabled by default.
+  impeller_trace_all_gl_calls = false
+
+  # Enable experimental 3D scene rendering.
+  impeller_enable_3d = false
+
+  # Enable to get trace statements for canvas usage.
+  impeller_trace_canvas = false
+}
+
+# Arguments that are combinations of other arguments by default but which can
+# be overridden by the user.
+
+declare_args() {
+  # Wether to build and include the validation layers.
+  impeller_enable_vulkan_validation_layers =
+      impeller_enable_vulkan && flutter_runtime_mode == "debug" &&
+      target_cpu == "arm64"
+
+  # Whether Impeller supports rendering on the platform.
+  impeller_supports_rendering =
+      impeller_enable_metal || impeller_enable_opengles ||
+      impeller_enable_vulkan
+
+  impeller_enable_compute = impeller_enable_vulkan || impeller_enable_metal
+}

impeller/tools/compiler.gni

@@ -0,0 +1,291 @@
+# Copyright 2013 The Flutter Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//build/compiled_action.gni")
+import("//flutter/impeller/tools/args.gni")
+
+# Dispatches to the build or prebuilt impellerc depending on the value of
+# the `impeller_use_prebuilt_impellerc` argument.
+# * When the `single_invocation` argument is false, all variables are
+#   forwarded to `compiled_action_foreach` or `action_foreach`, which will
+#   invoke `impellerc` separately for each source.
+# * When the `single_invocation` argument is true, `impellerc` is only
+#   invoked once via `compiled_action` or `action`.
+template("_impellerc") {
+  if (invoker.single_invocation) {
+    if (impeller_use_prebuilt_impellerc == "") {
+      compiled_action(target_name) {
+        forward_variables_from(invoker, "*")
+        tool = "//flutter/impeller/compiler:impellerc"
+      }
+    } else {
+      action(target_name) {
+        forward_variables_from(invoker, "*", [ "args" ])
+        script = "//build/gn_run_binary.py"
+        impellerc_path =
+            rebase_path(impeller_use_prebuilt_impellerc, root_build_dir)
+        args = [ impellerc_path ] + invoker.args
+      }
+    }
+  } else {
+    if (impeller_use_prebuilt_impellerc == "") {
+      compiled_action_foreach(target_name) {
+        forward_variables_from(invoker, "*")
+        tool = "//flutter/impeller/compiler:impellerc"
+      }
+    } else {
+      action_foreach(target_name) {
+        forward_variables_from(invoker, "*", [ "args" ])
+        script = "//build/gn_run_binary.py"
+        impellerc_path =
+            rebase_path(impeller_use_prebuilt_impellerc, root_build_dir)
+        args = [ impellerc_path ] + invoker.args
+      }
+    }
+  }
+}
+
+# Required: shaders                 The list of shaders inputs to compile.
+# Required: shader_target_flags     The target flag(s) to append. Valid options:
+#                                       --sksl
+#                                       --metal-ios
+#                                       --metal-desktop
+#                                       --opengl-es
+#                                       --opengl-desktop
+#                                       --vulkan
+#                                       --runtime-stage-metal
+#                                       --runtime-stage-gles
+#                                       --runtime-stage-vulkan
+#                                   Not required for --shader_bundle mode.
+# Required: sl_file_extension       The file extension to use for output files.
+#                                   Not required for --shader_bundle mode.
+# Optional: iplr                    Causes --sl output to be in iplr/runtime
+#                                   stage flatbuffer format.
+# Optional: shader_bundle           Specifies a Flutter GPU shader bundle
+#                                   configuration.
+#   Required: shader_bundle_output  Specifies the output filename of the shader
+#                                   bundle. This is only required if
+#                                   shader_bundle is supplied.
+# Optional: defines                 Specifies a list of valueless macro
+#                                   definitions.
+# Optional: intermediates_subdir    Specifies the subdirectory in which to put
+#                                   intermediates.
+# Optional: json                    Causes output format to be JSON instead of
+#                                   flatbuffer.
+template("impellerc") {
+  assert(defined(invoker.shaders), "Impeller shaders must be specified.")
+  assert(defined(invoker.shader_target_flags) || defined(invoker.shader_bundle),
+         "The flag to impellerc for target selection must be specified.")
+  assert(defined(invoker.sl_file_extension) || defined(invoker.shader_bundle),
+         "The extension of the SL file must be specified (metal, glsl, etc..).")
+  if (defined(invoker.shader_bundle)) {
+    assert(
+        defined(invoker.shader_bundle_output),
+        "When shader_bundle is specified, shader_bundle_output must also be specified.")
+  }
+
+  if (defined(invoker.shader_target_flags)) {
+    shader_target_flags = invoker.shader_target_flags
+  } else {
+    shader_target_flags = []
+  }
+
+  sksl = false
+  foreach(shader_target_flag, shader_target_flags) {
+    sksl = shader_target_flag == "--sksl"
+  }
+  iplr = false
+  if (defined(invoker.iplr) && invoker.iplr) {
+    iplr = invoker.iplr
+  }
+  json = false
+  if (defined(invoker.json) && invoker.json) {
+    json = invoker.json
+  }
+
+  # Not needed on every path.
+  not_needed([
+               "iplr",
+               "sksl",
+               "shader_bundle",
+               "shader_bundle_output",
+             ])
+
+  _impellerc(target_name) {
+    pool = "//build/toolchain:toolchain_pool"
+    shader_bundle = defined(invoker.shader_bundle)
+
+    # When single_invocation is true, impellerc will be invoked exactly once. When it's
+    # false, impellerc be invoked for each of the source file entries (invoker.shaders).
+    single_invocation = shader_bundle
+
+    if (defined(invoker.intermediates_subdir)) {
+      subdir = invoker.intermediates_subdir
+      generated_dir = "$target_gen_dir/$subdir"
+    } else {
+      generated_dir = "$target_gen_dir"
+    }
+
+    shader_lib_dir = rebase_path("//flutter/impeller/compiler/shader_lib")
+    args = [ "--include=$shader_lib_dir" ] + shader_target_flags
+
+    # When we're in single invocation mode, we can't use source enumeration.
+    if (!single_invocation) {
+      depfile_path = "$generated_dir/{{source_file_part}}.d"
+      depfile_intermediate_path = rebase_path(depfile_path, root_build_dir)
+      depfile = depfile_path
+      args += [
+        "--input={{source}}",
+        "--include={{source_dir}}",
+        "--depfile=$depfile_intermediate_path",
+      ]
+
+      if (defined(invoker.shader_target_flag)) {
+        args += [ "${invoker.shader_target_flag}" ]
+      }
+    }
+
+    if (defined(invoker.gles_language_version)) {
+      gles_language_version = invoker.gles_language_version
+      args += [ "--gles-language-version=$gles_language_version" ]
+    }
+
+    if (defined(invoker.metal_version)) {
+      assert(is_mac || is_ios)
+      metal_version = invoker.metal_version
+      args += [ "--metal-version=$metal_version" ]
+    }
+
+    if (defined(invoker.use_half_textures) && invoker.use_half_textures) {
+      args += [ "--use-half-textures" ]
+    }
+    if (defined(invoker.require_framebuffer_fetch) &&
+        invoker.require_framebuffer_fetch) {
+      args += [ "--require-framebuffer-fetch" ]
+    }
+
+    if (json) {
+      args += [ "--json" ]
+    }
+
+    if (iplr) {
+      # When building in IPLR mode, the compiler may be executed twice
+      args += [ "--iplr" ]
+    }
+
+    # The `sl_output` is the raw shader file output by the compiler. For --iplr
+    # and --shader-bundle, this is used as the filename for the flatbuffer to
+    # output.
+
+    if (shader_bundle) {
+      # When a shader bundle is specified, don't bother supplying flags for
+      # the reflection state as these are ignored. In this mode, the compiler
+      # is invoked multiple times and the reflection state for each shader is
+      # written to the output flatbuffer.
+      sl_output = "$generated_dir/${invoker.shader_bundle_output}"
+      sl_output_path = rebase_path(sl_output, root_build_dir)
+
+      args += [
+        "--sl=$sl_output_path",
+        "--shader-bundle=${invoker.shader_bundle}",
+      ]
+
+      outputs = [ sl_output ]
+    } else if (sksl) {
+      # When SkSL is selected as a `shader_target_flags`, don't generate
+      # C++ reflection state. Nothing needs to use it and it's likely invalid
+      # given the special cases when generating SkSL.
+      # Note that this configuration is orthogonal to the "--iplr" flag
+      sl_output =
+          "$generated_dir/{{source_file_part}}.${invoker.sl_file_extension}"
+      sl_output_path = rebase_path(sl_output, root_build_dir)
+
+      spirv_intermediate = "$generated_dir/{{source_file_part}}.spirv"
+      spirv_intermediate_path = rebase_path(spirv_intermediate, root_build_dir)
+      args += [
+        "--sl=$sl_output_path",
+        "--spirv=$spirv_intermediate_path",
+      ]
+
+      outputs = [ sl_output ]
+    } else {
+      # The default branch. Here we just generate one shader along with all of
+      # its C++ reflection state.
+
+      sl_output =
+          "$generated_dir/{{source_file_part}}.${invoker.sl_file_extension}"
+      sl_output_path = rebase_path(sl_output, root_build_dir)
+
+      reflection_json_intermediate = "$generated_dir/{{source_file_part}}.json"
+      reflection_header_intermediate = "$generated_dir/{{source_file_part}}.h"
+      reflection_cc_intermediate = "$generated_dir/{{source_file_part}}.cc"
+
+      spirv_intermediate = "$generated_dir/{{source_file_part}}.spirv"
+      spirv_intermediate_path = rebase_path(spirv_intermediate, root_build_dir)
+      reflection_json_path =
+          rebase_path(reflection_json_intermediate, root_build_dir)
+      reflection_header_path =
+          rebase_path(reflection_header_intermediate, root_build_dir)
+      reflection_cc_path =
+          rebase_path(reflection_cc_intermediate, root_build_dir)
+
+      args += [
+        "--sl=$sl_output_path",
+        "--spirv=$spirv_intermediate_path",
+        "--reflection-json=$reflection_json_path",
+        "--reflection-header=$reflection_header_path",
+        "--reflection-cc=$reflection_cc_path",
+      ]
+
+      outputs = [
+        sl_output,
+        reflection_header_intermediate,
+        reflection_cc_intermediate,
+      ]
+    }
+
+    if (defined(invoker.defines)) {
+      foreach(def, invoker.defines) {
+        args += [ "--define=$def" ]
+      }
+    }
+
+    if (single_invocation) {
+      inputs = invoker.shaders
+    } else {
+      sources = invoker.shaders
+    }
+  }
+}
+
+template("impellerc_reflect") {
+  assert(
+      defined(invoker.impellerc_invocation),
+      "The target that specifies the ImpellerC invocation to reflect must be defined.")
+
+  reflect_config = "reflect_$target_name"
+  config(reflect_config) {
+    include_dirs = [ get_path_info(
+            get_label_info("//flutter/impeller:impeller", "target_gen_dir"),
+            "dir") ]
+  }
+
+  impellerc_invocation = invoker.impellerc_invocation
+
+  source_set(target_name) {
+    public_configs = [ ":$reflect_config" ]
+    public = filter_include(get_target_outputs(impellerc_invocation), [ "*.h" ])
+    sources = filter_include(get_target_outputs(impellerc_invocation),
+                             [
+                               "*.h",
+                               "*.cc",
+                               "*.mm",
+                             ])
+
+    deps = [
+      "//flutter/impeller/core",
+      impellerc_invocation,
+    ]
+  }
+}