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Tint Architecture
┏━━━━━━━━┓ ┏━━━━━━┓
┃ SPIR━V ┃ ┃ WGSL ┃
┗━━━━┃━━━┛ ┗━━━┃━━┛
▼ ▼
┏━━━━━━━━━┃━━━━━━━━━━━━━━━━━━━━━━━━━━━┃━━━━━━━━┓
┃ ┃ Reader ┃ ┃
┃ ┃ ┃ ┃
┃ ┏━━━━━━━┻━━━━━━┓ ┏━━━━━━┻━━━━━━┓ ┃
┃ ┃ SPIRV-Reader ┃ ┃ WGSL-Reader ┃ ┃
┃ ┗━━━━━━━━━━━━━━┛ ┗━━━━━━━━━━━━━┛ ┃
┗━━━━━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━━━┛
▼
┏━━━━━━━━━━━━━━━━━┻━━━━━━━━━━━━━━━━━┓
┃ ProgramBuilder ┃
┃ (mutable) ┃
┏━━━━━━━━━━━━►┫ ┏━━━━━┓ ┏━━━━━━━┓ ┏━━━━━━━━━┓ ┃
┃ ┃ ┃ AST ┃ ┃ Types ┃ ┃ Symbols ┃ ┃
┃ ┃ ┗━━━━━┛ ┗━━━━━━━┛ ┗━━━━━━━━━┛ ┃
┃ ┗━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━┛
┃ ▼
┃ ┌┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┃┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┐
▲ ┆ Build ▼ ┆
┏━━━┻━━━┓ ┆ ┏━━━━━━━━┻━━━━━━━━┓ ┆
┃ Clone ┃ ┆ ┃ Type Determiner ┃ ┆
┗━━━┳━━━┛ ┆ ┗━━━━━━━━━━━━━━━━━┛ ┆
▲ └┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┃┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┘
┃ ▼
┃ ┏━━━━━━━━━━━━━━━━━━━━━━━┻━━━━━━━━━━━━━━━━━━━━━━┓
┃ ┃ Program ┃
┃ ┃ (immutable) ┃
┣━━━━━━◄┫ ┏━━━━━┓ ┏━━━━━━━┓ ┏━━━━━━━━━━┓ ┏━━━━━━━━━┓ ┃
┃ ┃ ┃ AST ┃ ┃ Types ┃ ┃ Semantic ┃ ┃ Symbols ┃ ┃
┃ ┃ ┗━━━━━┛ ┗━━━━━━━┛ ┗━━━━━━━━━━┛ ┗━━━━━━━━━┛ ┃
┃ ┗━━━━━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━━━┛
▲ ▼
┏━━━━━┻━━━━━┓ ┏━━━━━┻━━━━━┓ ┏━━━━━━━━━━━┓
┃ Transform ┃◄━━━━━━━━━━━━━━━━━◄┃ Validator ┣━━━━━━►┃ Inspector ┃
┗━━━━━━━━━━━┛ ┗━━━━━┳━━━━━┛ ┗━━━━━━━━━━━┛
▼
┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┻━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ Writer ┃
┃ ┃
┃ ┏━━━━━━━━━━━━━━┓ ┏━━━━━━━━━━━━━┓ ┏━━━━━━━━━━━━━┓ ┏━━━━━━━━━━━━┓ ┃
┃ ┃ SPIRV-Writer ┃ ┃ WGSL-Writer ┃ ┃ HLSL-Writer ┃ ┃ MSL-Writer ┃ ┃
┃ ┗━━━━━━━┳━━━━━━┛ ┗━━━━━━┳━━━━━━┛ ┗━━━━━━┳━━━━━━┛ ┗━━━━━━┳━━━━━┛ ┃
┗━━━━━━━━━┃━━━━━━━━━━━━━━━━━━┃━━━━━━━━━━━━━━━━━━┃━━━━━━━━━━━━━━━━━━┃━━━━━━━┛
▼ ▼ ▼ ▼
┏━━━━┻━━━┓ ┏━━━┻━━┓ ┏━━━┻━━┓ ┏━━┻━━┓
┃ SPIR-V ┃ ┃ WGSL ┃ ┃ HLSL ┃ ┃ MSL ┃
┗━━━━━━━━┛ ┗━━━━━━┛ ┗━━━━━━┛ ┗━━━━━┛
Reader
Readers are responsible for parsing a shader program and populating a
ProgramBuilder with the parsed AST, type and symbol information.
The WGSL reader is a recursive descent parser. It closely follows the WGSL grammar in the naming of the parse methods.
ProgramBuilder
A ProgramBuilder is the primary interface to construct an immutable Program.
There are a number of methods exposed which make creating of the Program
simpler. A ProgramBuilder can only be used once, and must be discarded after
the Program is constructed.
A Program is built from the ProgramBuilder by std::move()ing the
ProgramBuilder to a new Program object. When built, type determination is
run so the produced Program will contain all the needed semantic information.
At any time before building the Program, ProgramBuilder::IsValid() may be
called to ensure the AST is structurally correct. This checks that things
like if statements have a condition and body attached.
If further changes to the Program are needed (say via a Transform) then a
new ProgramBuilder can be produced by cloning the Program into a new
ProgramBuilder.
Unlike Programs, ProgramBuilders are not part of the public Tint API.
AST
The Abstract Syntax Tree is a directed acyclic graph of ast::Nodes which
encode the syntactic structure of the WGSL program.
The root of the AST is the ast::Module class which holds each of the declared
functions, variables and user defined types (type aliases and structures).
Each ast::Node represents a single part of the program's source, and so
ast::Nodes are not shared.
The AST does not perform any verification of its content. For example, the
ast::StrideDecoration node has numeric stride parameter, which is a count of
the number of bytes from the start of one array element to the start of the
next. The AST node itself does not constrain the set of stride values that you
can set, aside from storing it as an unsigned integer.
Types
Types are constructed during the Reader and Type Determination phases, and are
held by the Program or ProgramBuilder. AST and semantic nodes can both
reference types.
Each type::Type node uniquely represents a particular spelling of a WGSL
type within the program, so you can compare type::Type* pointers to check for
equivalence of type expressions.
For example, there is only one type::Type node for the i32 type, no matter
how many times it is mentioned in the source program.
However, if MyI32 is a type alias for i32, then they will have two different
type nodes.
Semantic information
Semantic information is held by semantic::Nodes which describe the program at
a higher / more abstract level than the AST. This includes information such as
the resolved type of each expression, the resolved overload of an intrinsic
function call, and the module scoped variables used by each function.
Semantic information is generated by the TypeDeterminer when the Program
is built from a ProgramBuilder.
The semantic::Info class holds a map of ast::Nodes to semantic::Nodes.
This map is many-to-one - i.e. while a AST node might have a single
corresponding semantic node, the reverse may not be true. For example:
many ast::IdentifierExpression nodes may map to a single semantic::Variable,
and so the semantic::Variable does not have a single corresponding
ast::Node.
Unlike ast::Nodes, semantic nodes may not necessarily form a directed acyclic
graph, and the semantic graph may contain diamonds.
Symbols
Symbols represent a unique string identifier in the source program. These string
identifiers are transformed into symbols within the Readers.
During the Writer phase, symbols may be emitted as strings using a Namer.
A Namer may output the symbol in any form that preserves the uniqueness of
that symbol.
Type Determiner
The TypeDeterminer will automatically run when a Program is built.
A TypeDeterminer creates the Programs semantic information by analyzing the
Programs AST and type information.
The TypeDeterminer will do the minimal amount of validation required in order
to always be accessing valid nodes, reporting any errors found in the
Program's diagnostics. Even if the TypeDeterminer doesn't generate any
errors doesn't mean the generated Program is semantically valid. Use the
Validator to check for a Program's final validity.
Program
A Program holds an immutable version of the information from the
ProgramBuilder along with semantic information generated by the
TypeDeterminer.
Like ProgramBuilder, Program::IsValid() may be called to ensure the AST is
structurally correct and that the TypeDeterminer did not report any errors.
Program::IsValid() does not perform semantic validation, use the Validator
to check for a Program's final validity.
Unlike the ProgramBuilder, a Program is fully immutable, and is part of the
public Tint API. The immutable nature of Programs make these entirely safe
to share between multiple threads without the use of synchronization primitives.
Validation
The Validator checks a Program for static validity as specified by the WGSL
language, and reports any validation errors found. Attempting to pass a
Program that does not pass validation on to later stages will result in
undefined behavior.
Inspector
The inspectors job is to go through the Program and pull out various pieces of
information. The information may be used to pass information into the downstream
compilers (things like specialization constants) or may be used to pass into
transforms to update the AST before generating the resulting code.
The input Program to the inspector must be valid (pass validation).
Transforms
There maybe various transforms we want to run over the Program.
This is for things like Vertex Pulling or Robust Buffer Access.
A transform operates by cloning the input Program into a new ProgramBuilder,
applying the required changes, and then finally building and returning a new
output Program. As type determination is always run when a Program is built,
Transforms will always emit a Program with semantic information.
The input Program to a transform must be valid (pass validation).
If the input Program of a transform is valid then the transform must guarantee
that the output program is also valid.
Writers
A writer is responsible for writing the Program in the target shader language.
The input Program to a writer must be valid (pass validation).