[Impeller] use SSBOs for gradients where supported (metal/vulkan) (#37654)

* [Impeller] use uniform array for more efficient small gradients

* ++

* Make this work on Android

* ++

* ++

* ++

* compiler support and basic feature detection

* ++

* ++

* rename to ssbo_fill, move to context

* ++

* ++

* ++

* tests

* ++

* ++

Author: Jonah Williams

ci/licenses_golden/licenses_flutter

@@ -1121,6 +1121,7 @@ FILE: ../../../flutter/impeller/compiler/shader_lib/impeller/branching.glsl
 FILE: ../../../flutter/impeller/compiler/shader_lib/impeller/color.glsl
 FILE: ../../../flutter/impeller/compiler/shader_lib/impeller/constants.glsl
 FILE: ../../../flutter/impeller/compiler/shader_lib/impeller/gaussian.glsl
+FILE: ../../../flutter/impeller/compiler/shader_lib/impeller/gradient.glsl
 FILE: ../../../flutter/impeller/compiler/shader_lib/impeller/texture.glsl
 FILE: ../../../flutter/impeller/compiler/shader_lib/impeller/transform.glsl
 FILE: ../../../flutter/impeller/compiler/shader_lib/impeller/types.glsl
@@ -1291,6 +1292,7 @@ FILE: ../../../flutter/impeller/entity/shaders/glyph_atlas_sdf.frag
 FILE: ../../../flutter/impeller/entity/shaders/glyph_atlas_sdf.vert
 FILE: ../../../flutter/impeller/entity/shaders/gradient_fill.vert
 FILE: ../../../flutter/impeller/entity/shaders/linear_gradient_fill.frag
+FILE: ../../../flutter/impeller/entity/shaders/linear_gradient_ssbo_fill.frag
 FILE: ../../../flutter/impeller/entity/shaders/linear_to_srgb_filter.frag
 FILE: ../../../flutter/impeller/entity/shaders/linear_to_srgb_filter.vert
 FILE: ../../../flutter/impeller/entity/shaders/morphology_filter.frag
@@ -1299,6 +1301,7 @@ FILE: ../../../flutter/impeller/entity/shaders/position.vert
 FILE: ../../../flutter/impeller/entity/shaders/position_color.vert
 FILE: ../../../flutter/impeller/entity/shaders/position_uv.vert
 FILE: ../../../flutter/impeller/entity/shaders/radial_gradient_fill.frag
+FILE: ../../../flutter/impeller/entity/shaders/radial_gradient_ssbo_fill.frag
 FILE: ../../../flutter/impeller/entity/shaders/rrect_blur.frag
 FILE: ../../../flutter/impeller/entity/shaders/rrect_blur.vert
 FILE: ../../../flutter/impeller/entity/shaders/runtime_effect.vert
@@ -1307,6 +1310,7 @@ FILE: ../../../flutter/impeller/entity/shaders/solid_fill.vert
 FILE: ../../../flutter/impeller/entity/shaders/srgb_to_linear_filter.frag
 FILE: ../../../flutter/impeller/entity/shaders/srgb_to_linear_filter.vert
 FILE: ../../../flutter/impeller/entity/shaders/sweep_gradient_fill.frag
+FILE: ../../../flutter/impeller/entity/shaders/sweep_gradient_ssbo_fill.frag
 FILE: ../../../flutter/impeller/entity/shaders/texture_fill.frag
 FILE: ../../../flutter/impeller/entity/shaders/texture_fill.vert
 FILE: ../../../flutter/impeller/entity/shaders/tiled_texture_fill.frag
@@ -1490,6 +1494,7 @@ FILE: ../../../flutter/impeller/renderer/backend/vulkan/texture_vk.h
 FILE: ../../../flutter/impeller/renderer/backend/vulkan/vertex_descriptor_vk.cc
 FILE: ../../../flutter/impeller/renderer/backend/vulkan/vertex_descriptor_vk.h
 FILE: ../../../flutter/impeller/renderer/backend/vulkan/vk.h
+FILE: ../../../flutter/impeller/renderer/backend_features.h
 FILE: ../../../flutter/impeller/renderer/blit_command.cc
 FILE: ../../../flutter/impeller/renderer/blit_command.h
 FILE: ../../../flutter/impeller/renderer/blit_pass.cc

impeller/compiler/code_gen_template.h

@@ -202,7 +202,6 @@ using Shader = {{camel_case(shader_name)}}{{camel_case(shader_stage)}}Shader;
 // Sanity checks for {{def.name}}
 {% if last(def.members).array_elements == 0 %}
 static_assert(std::is_standard_layout_v<Shader::{{def.name}}<0>>);
-static_assert(sizeof(Shader::{{def.name}}<0>) == {{def.byte_length}});
 {% for member in def.members %}
 static_assert(offsetof(Shader::{{def.name}}<0>, {{member.name}}) == {{member.offset}});
 {% endfor %}

impeller/compiler/compiler.cc

@@ -45,10 +45,14 @@ static CompilerBackend CreateGLSLCompiler(const spirv_cross::ParsedIR& ir,
   sl_options.force_zero_initialized_variables = true;
   sl_options.vertex.fixup_clipspace = true;
   if (source_options.target_platform == TargetPlatform::kOpenGLES) {
-    sl_options.version = 100;
+    sl_options.version = source_options.gles_language_version > 0
+                             ? source_options.gles_language_version
+                             : 100;
     sl_options.es = true;
   } else {
-    sl_options.version = 120;
+    sl_options.version = source_options.gles_language_version > 0
+                             ? source_options.gles_language_version
+                             : 120;
     sl_options.es = false;
   }
   gl_compiler->set_common_options(sl_options);

impeller/compiler/impellerc_main.cc

@@ -73,6 +73,7 @@ bool Main(const fml::CommandLine& command_line) {
       switches.source_file_name, options.type, options.source_language,
       switches.entry_point);
   options.json_format = switches.json_format;
+  options.gles_language_version = switches.gles_language_version;
 
   Reflector::Options reflector_options;
   reflector_options.target_platform = switches.target_platform;

impeller/compiler/shader_lib/impeller/BUILD.gn

@@ -9,6 +9,7 @@ copy("impeller") {
     "color.glsl",
     "constants.glsl",
     "gaussian.glsl",
+    "gradient.glsl",
     "texture.glsl",
     "transform.glsl",
     "types.glsl",

impeller/compiler/shader_lib/impeller/gradient.glsl

@@ -0,0 +1,24 @@
+// 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.
+
+#ifndef GRADIENT_GLSL_
+#define GRADIENT_GLSL_
+
+#include <impeller/texture.glsl>
+
+/// Compute the indexes and mix coefficient used to mix colors for an
+/// arbitrarily sized color gradient.
+///
+/// The returned values are the lower index, upper index, and mix
+/// coefficient.
+vec3 IPComputeFixedGradientValues(float t, float colors_length) {
+  float rough_index = (colors_length - 1) * t;
+  float lower_index = floor(rough_index);
+  float upper_index = ceil(rough_index);
+  float scale = rough_index - lower_index;
+
+  return vec3(lower_index, upper_index, scale);
+}
+
+#endif

impeller/compiler/source_options.h

@@ -24,6 +24,7 @@ struct SourceOptions {
   std::vector<IncludeDir> include_dirs;
   std::string file_name = "main.glsl";
   std::string entry_point_name = "main";
+  uint32_t gles_language_version = 100;
   std::vector<std::string> defines;
   bool json_format = false;
 

impeller/compiler/switches.cc

@@ -69,6 +69,7 @@ void Switches::PrintHelp(std::ostream& stream) {
   stream << "[optional,multiple] --include=<include_directory>" << std::endl;
   stream << "[optional,multiple] --define=<define>" << std::endl;
   stream << "[optional] --depfile=<depfile_path>" << std::endl;
+  stream << "[optional] --gles-language-verision=<number>" << std::endl;
   stream << "[optional] --json" << std::endl;
 }
 
@@ -124,6 +125,9 @@ Switches::Switches(const fml::CommandLine& command_line)
           command_line.GetOptionValueWithDefault("reflection-cc", "")),
       depfile_path(command_line.GetOptionValueWithDefault("depfile", "")),
       json_format(command_line.HasOption("json")),
+      gles_language_version(
+          stoi(command_line.GetOptionValueWithDefault("gles-language-version",
+                                                      "0"))),
       entry_point(
           command_line.GetOptionValueWithDefault("entry-point", "main")) {
   if (!working_directory || !working_directory->is_valid()) {

impeller/compiler/switches.h

@@ -33,6 +33,7 @@ struct Switches {
   std::vector<std::string> defines;
   bool json_format;
   SourceLanguage source_language = SourceLanguage::kUnknown;
+  uint32_t gles_language_version;
   std::string entry_point;
 
   Switches();

impeller/entity/BUILD.gn

@@ -66,6 +66,20 @@ impeller_shaders("entity_shaders") {
   ]
 }
 
+impeller_shaders("modern_entity_shaders") {
+  name = "modern"
+
+  if (impeller_enable_opengles) {
+    gles_language_version = "460"
+  }
+
+  shaders = [
+    "shaders/linear_gradient_ssbo_fill.frag",
+    "shaders/radial_gradient_ssbo_fill.frag",
+    "shaders/sweep_gradient_ssbo_fill.frag",
+  ]
+}
+
 impeller_component("entity") {
   sources = [
     "contents/atlas_contents.cc",
@@ -146,6 +160,7 @@ impeller_component("entity") {
 
   public_deps = [
     ":entity_shaders",
+    ":modern_entity_shaders",
     "../archivist",
     "../image",
     "../renderer",