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* Copyright 2022 Google Inc.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#include "include/private/SkSLDefines.h"
#include "include/private/SkTHash.h"
#include "src/sksl/codegen/SkSLCodeGenerator.h"
#include <cstdint>
#include <string_view>
#include <type_traits>
#include <utility>
namespace sknonstd {
template <typename T> struct is_bitmask_enum;
} // namespace sknonstd
namespace SkSL {
class AnyConstructor;
class BinaryExpression;
class Block;
class Context;
class ConstructorCompound;
class Expression;
class ExpressionStatement;
class FieldAccess;
class FunctionDeclaration;
class FunctionDefinition;
class Literal;
class OutputStream;
class ProgramElement;
class ReturnStatement;
class Statement;
class Type;
class VarDeclaration;
class VariableReference;
enum class OperatorPrecedence : uint8_t;
struct Modifiers;
struct Program;
struct Swizzle;
* Convert a Program into WGSL code.
class WGSLCodeGenerator : public CodeGenerator {
// See
enum class Builtin {
// Vertex stage:
kVertexIndex, // input
kInstanceIndex, // input
kPosition, // output, fragment stage input
// Fragment stage:
kFrontFacing, // input
kSampleIndex, // input
kFragDepth, // output
kSampleMask, // input, output
// Compute stage:
kLocalInvocationId, // input
kLocalInvocationIndex, // input
kGlobalInvocationId, // input
kWorkgroupId, // input
kNumWorkgroups, // input
// Represents a function's dependencies that are not accessible in global scope. For instance,
// pipeline stage input and output parameters must be passed in as an argument.
// This is a bitmask enum.
enum class FunctionDependencies : uint8_t {
kNone = 0,
kPipelineInputs = 1,
kPipelineOutputs = 2,
// Variable declarations can be terminated by:
// - comma (","), e.g. in struct member declarations or function parameters
// - semicolon (";"), e.g. in function scope variables
// A "none" option is provided to skip the delimiter when not needed, e.g. at the end of a list
// of declarations.
enum class Delimiter {
struct ProgramRequirements {
using DepsMap = SkTHashMap<const FunctionDeclaration*, FunctionDependencies>;
ProgramRequirements() = default;
ProgramRequirements(DepsMap dependencies, bool mainNeedsCoordsArgument)
: dependencies(std::move(dependencies))
, mainNeedsCoordsArgument(mainNeedsCoordsArgument) {}
// Mappings used to synthesize function parameters according to dependencies on pipeline
// input/output variables.
DepsMap dependencies;
// True, if the main function takes a coordinate parameter. This is used to ensure that
// sk_FragCoord is declared as part of pipeline inputs.
bool mainNeedsCoordsArgument;
WGSLCodeGenerator(const Context* context, const Program* program, OutputStream* out)
: INHERITED(context, program, out) {}
bool generateCode() override;
using INHERITED = CodeGenerator;
using Precedence = OperatorPrecedence;
// Called by generateCode() as the first step.
void preprocessProgram();
// Write output content while correctly handling indentation.
void write(std::string_view s);
void writeLine(std::string_view s = std::string_view());
void finishLine();
void writeName(std::string_view name);
// Helpers to declare a pipeline stage IO parameter declaration.
void writePipelineIODeclaration(Modifiers modifiers,
const Type& type,
std::string_view name,
Delimiter delimiter);
void writeUserDefinedIODecl(const Type& type,
std::string_view name,
int location,
Delimiter delimiter);
void writeBuiltinIODecl(const Type& type,
std::string_view name,
Builtin builtin,
Delimiter delimiter);
// Write a function definition.
void writeFunction(const FunctionDefinition& f);
void writeFunctionDeclaration(const FunctionDeclaration& f);
// Write the program entry point.
void writeEntryPoint(const FunctionDefinition& f);
// Writers for supported statement types.
void writeStatement(const Statement& s);
void writeStatements(const StatementArray& statements);
void writeBlock(const Block& b);
void writeExpressionStatement(const ExpressionStatement& s);
void writeReturnStatement(const ReturnStatement& s);
void writeVarDeclaration(const VarDeclaration& varDecl);
// Writers for expressions.
void writeExpression(const Expression& e, Precedence parentPrecedence);
void writeBinaryExpression(const BinaryExpression& b, Precedence parentPrecedence);
void writeFieldAccess(const FieldAccess& f);
void writeLiteral(const Literal& l);
void writeSwizzle(const Swizzle& swizzle);
void writeVariableReference(const VariableReference& r);
// Constructor expressions
void writeAnyConstructor(const AnyConstructor& c, Precedence parentPrecedence);
void writeConstructorCompound(const ConstructorCompound& c, Precedence parentPrecedence);
void writeConstructorCompoundVector(const ConstructorCompound& c, Precedence parentPrecedence);
// Generic recursive ProgramElement visitor.
void writeProgramElement(const ProgramElement& e);
// We bundle all varying pipeline stage inputs and outputs in a struct.
void writeStageInputStruct();
void writeStageOutputStruct();
// Stores the disallowed identifier names.
// TODO(skia:13092): populate this
SkTHashSet<std::string_view> fReservedWords;
ProgramRequirements fRequirements;
int fPipelineInputCount = 0;
// Output processing state.
int fIndentation = 0;
bool fAtLineStart = false;
} // namespace SkSL
namespace sknonstd {
template <>
struct is_bitmask_enum<SkSL::WGSLCodeGenerator::FunctionDependencies> : std::true_type {};
} // namespace sknonstd