[Impeller] Allow metal shaders to compile through SPIR-V with openGL semantics. (#40616)

[Impeller] Allow metal shaders to compile through SPIR-V with openGL semantics.

Author: jonahwilliams

impeller/compiler/compiler.cc

@@ -366,6 +366,22 @@ Compiler::Compiler(const fml::Mapping& source_mapping,
   switch (source_options.target_platform) {
     case TargetPlatform::kMetalDesktop:
     case TargetPlatform::kMetalIOS:
+      spirv_options.SetOptimizationLevel(
+          shaderc_optimization_level::shaderc_optimization_level_performance);
+      if (source_options.use_half_textures) {
+        spirv_options.SetTargetEnvironment(
+            shaderc_target_env::shaderc_target_env_opengl,
+            shaderc_env_version::shaderc_env_version_opengl_4_5);
+        spirv_options.SetTargetSpirv(
+            shaderc_spirv_version::shaderc_spirv_version_1_0);
+      } else {
+        spirv_options.SetTargetEnvironment(
+            shaderc_target_env::shaderc_target_env_vulkan,
+            shaderc_env_version::shaderc_env_version_vulkan_1_1);
+        spirv_options.SetTargetSpirv(
+            shaderc_spirv_version::shaderc_spirv_version_1_3);
+      }
+      break;
     case TargetPlatform::kOpenGLES:
     case TargetPlatform::kOpenGLDesktop:
       spirv_options.SetOptimizationLevel(

impeller/compiler/impellerc_main.cc

@@ -75,6 +75,7 @@ bool Main(const fml::CommandLine& command_line) {
   options.json_format = switches.json_format;
   options.gles_language_version = switches.gles_language_version;
   options.metal_version = switches.metal_version;
+  options.use_half_textures = switches.use_half_textures;
 
   Reflector::Options reflector_options;
   reflector_options.target_platform = switches.target_platform;

impeller/compiler/source_options.h

@@ -29,6 +29,10 @@ struct SourceOptions {
   bool json_format = false;
   std::string metal_version;
 
+  /// @brief Whether half-precision textures should be supported, requiring
+  /// opengl semantics. Only used on metal targets.
+  bool use_half_textures = false;
+
   SourceOptions();
 
   ~SourceOptions();

impeller/compiler/switches.cc

@@ -72,8 +72,8 @@ void Switches::PrintHelp(std::ostream& stream) {
   stream << "[optional] --depfile=<depfile_path>" << std::endl;
   stream << "[optional] --gles-language-verision=<number>" << std::endl;
   stream << "[optional] --json" << std::endl;
-  stream << "[optional] --remap-samplers (force metal sampler index to match "
-            "declared order)"
+  stream << "[optional] --use-half-textures (force openGL semantics when "
+            "targeting metal)"
          << std::endl;
 }
 
@@ -135,7 +135,8 @@ Switches::Switches(const fml::CommandLine& command_line)
       metal_version(
           command_line.GetOptionValueWithDefault("metal-version", "1.2")),
       entry_point(
-          command_line.GetOptionValueWithDefault("entry-point", "main")) {
+          command_line.GetOptionValueWithDefault("entry-point", "main")),
+      use_half_textures(command_line.HasOption("use-half-textures")) {
   auto language =
       command_line.GetOptionValueWithDefault("source-language", "glsl");
   std::transform(language.begin(), language.end(), language.begin(),

impeller/compiler/switches.h

@@ -19,23 +19,24 @@ namespace compiler {
 
 struct Switches {
   TargetPlatform target_platform = TargetPlatform::kUnknown;
-  std::shared_ptr<fml::UniqueFD> working_directory;
-  std::vector<IncludeDir> include_directories;
-  std::string source_file_name;
-  SourceType input_type;
-  std::string sl_file_name;
-  bool iplr;
-  std::string spirv_file_name;
-  std::string reflection_json_name;
-  std::string reflection_header_name;
-  std::string reflection_cc_name;
-  std::string depfile_path;
-  std::vector<std::string> defines;
-  bool json_format;
+  std::shared_ptr<fml::UniqueFD> working_directory = nullptr;
+  std::vector<IncludeDir> include_directories = {};
+  std::string source_file_name = "";
+  SourceType input_type = SourceType::kUnknown;
+  std::string sl_file_name = "";
+  bool iplr = false;
+  std::string spirv_file_name = "";
+  std::string reflection_json_name = "";
+  std::string reflection_header_name = "";
+  std::string reflection_cc_name = "";
+  std::string depfile_path = "";
+  std::vector<std::string> defines = {};
+  bool json_format = false;
   SourceLanguage source_language = SourceLanguage::kUnknown;
-  uint32_t gles_language_version;
-  std::string metal_version;
-  std::string entry_point;
+  uint32_t gles_language_version = 0;
+  std::string metal_version = "";
+  std::string entry_point = "";
+  bool use_half_textures = false;
 
   Switches();
 

impeller/tools/impeller.gni

@@ -305,6 +305,10 @@ template("impellerc") {
       args += [ "--metal-version=$metal_version" ]
     }
 
+    if (defined(invoker.use_half_textures) && invoker.use_half_textures) {
+      args += [ "--use-half-textures" ]
+    }
+
     if (json) {
       args += [ "--json" ]
     }
@@ -403,6 +407,11 @@ template("_impeller_shaders_metal") {
     metal_version = invoker.metal_version
   }
 
+  use_half_textures = false
+  if (defined(invoker.use_half_textures) && invoker.use_half_textures) {
+    use_half_textures = invoker.use_half_textures
+  }
+
   shaders_base_name = string_join("",
                                   [
                                     invoker.name,
@@ -413,6 +422,7 @@ template("_impeller_shaders_metal") {
     shaders = invoker.shaders
     metal_version = metal_version
     sl_file_extension = "metal"
+    use_half_textures = use_half_textures
     shader_target_flag = ""
     defines = [ "IMPELLER_TARGET_METAL" ]
     if (is_ios) {
@@ -666,12 +676,26 @@ template("_impeller_shaders_vk") {
 #
 #    The SPIR-V version required by the shaders.
 #
+# @param[options] use_half_textures
+#
+#    Whether the metal shader is using half-precision textures and requires
+#    openGL semantics when compilig SPIR-V.
+#
 template("impeller_shaders") {
   metal_version = "1.2"
   if (defined(invoker.metal_version)) {
     metal_version = invoker.metal_version
   }
-  not_needed([ "metal_version" ])
+
+  use_half_textures = false
+  if (defined(invoker.use_half_textures) && invoker.use_half_textures) {
+    use_half_textures = true
+  }
+
+  not_needed([
+               "metal_version",
+               "use_half_textures",
+             ])
 
   enable_opengles = impeller_enable_opengles
   if (defined(invoker.enable_opengles)) {
@@ -685,6 +709,7 @@ template("impeller_shaders") {
       name = invoker.name
       shaders = invoker.shaders
       metal_version = metal_version
+      use_half_textures = use_half_textures
     }
   }