[impellerc] Namespace user functions (flutter/engine#35155)

engine/src/flutter/impeller/compiler/spirv_sksl.cc

@@ -38,6 +38,8 @@ std::string CompilerSkSL::compile() {
   backend.use_array_constructor = true;
   backend.workgroup_size_is_hidden = true;
 
+  fixup_user_functions();
+
   fixup_anonymous_struct_names();
   fixup_type_alias();
   reorder_type_alias();
@@ -72,6 +74,30 @@ std::string CompilerSkSL::compile() {
   return buffer.str();
 }
 
+void CompilerSkSL::fixup_user_functions() {
+  const std::string prefix = "__flutter_local_";
+  ir.for_each_typed_id<SPIRFunction>([&](uint32_t, const SPIRFunction& func) {
+    const auto& original_name = get_name(func.self);
+    // Just in case. Don't add the prefix a second time.
+    if (original_name.rfind(prefix, 0) == 0) {
+      return;
+    }
+    std::string new_name = prefix + original_name;
+    set_name(func.self, new_name);
+  });
+
+  ir.for_each_typed_id<SPIRFunctionPrototype>(
+      [&](uint32_t, const SPIRFunctionPrototype& func) {
+        const auto& original_name = get_name(func.self);
+        // Just in case. Don't add the prefix a second time.
+        if (original_name.rfind(prefix, 0) == 0) {
+          return;
+        }
+        std::string new_name = prefix + original_name;
+        set_name(func.self, new_name);
+      });
+}
+
 void CompilerSkSL::emit_header() {
   statement("// This SkSL shader is autogenerated by spirv-cross.");
   statement("");

engine/src/flutter/impeller/compiler/spirv_sksl.h

@@ -38,6 +38,8 @@ class CompilerSkSL : public spirv_cross::CompilerGLSL {
 
   void emit_uniform(const spirv_cross::SPIRVariable& var) override;
 
+  void fixup_user_functions();
+
   void detect_unsupported_resources();
   bool emit_constant_resources();
   bool emit_struct_resources();

engine/src/flutter/lib/ui/fixtures/shaders/general_shaders/BUILD.gn

@@ -11,6 +11,7 @@ if (enable_unittests) {
     "blue_green_sampler.frag",
     "children_and_uniforms.frag",
     "functions.frag",
+    "no_builtin_redefinition.frag",
     "no_uniforms.frag",
     "simple.frag",
     "uniforms.frag",

engine/src/flutter/lib/ui/fixtures/shaders/general_shaders/no_builtin_redefinition.frag

@@ -0,0 +1,38 @@
+#version 320 es
+
+// 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.
+
+precision highp float;
+
+layout ( location = 0 ) out vec4 oColor;
+
+layout ( location = 0 ) uniform float a;  // should be 1.0
+
+float saturate(float x) {
+  return clamp(x, 0.0, 1.0);
+}
+
+float addA(float x) {
+  return x + a;
+}
+
+vec2 pairWithA(float x) {
+  return vec2(x, a);
+}
+
+vec3 composedFunction(float x) {
+  return vec3(addA(x), pairWithA(x));
+}
+
+float multiParam(float x, float y, float z) {
+  return x * y * z * a;
+}
+
+void main() {
+  float x = saturate(addA(0.0)); // x = 0 + 1;
+  vec3 v3 = composedFunction(x); // v3 = vec3(2, 1, 1);
+  x = multiParam(v3.x, v3.y, v3.z); // x = 2 * 1 * 1 * 1;
+  oColor = vec4(0.0, x / 2.0, 0.0, 1.0); // vec4(0, 1, 0, 1);
+}

engine/src/flutter/testing/dart/fragment_shader_test.dart

@@ -118,6 +118,16 @@ void main() async {
     expect(throws, equals(true));
   });
 
+  test('user defined functions do not redefine builtins', () async {
+    final FragmentProgram program = await FragmentProgram.fromAsset(
+      'no_builtin_redefinition.frag.iplr',
+    );
+    final Shader shader = program.shader(
+      floatUniforms: Float32List.fromList(<double>[1.0]),
+    );
+    await _expectShaderRendersGreen(shader);
+  });
+
   test('fromAsset accepts a shader with no uniforms', () async {
     final FragmentProgram program = await FragmentProgram.fromAsset(
       'no_uniforms.frag.iplr',