+--------+ +------+
| SPIR-V | | WGSL |
+----|---+ +---|--+
| |
+---------|---------------------------|--------+
| | Reader | |
| | | |
| +-------|------+ +------|------+ |
| | SPIRV-Reader | | WGSL-Reader | |
| +--------------+ +-------------+ |
+-----------------------|----------------------+
|
+--|--+ +---------+
| AST |------| IsValid |
+--|--+ +---------+
|
+--------|--------+
| Type Determiner |
+--------|--------+
|
+-----|-----+
| Validator |
+-----|-----+
|
+-----|-----+
| Inspector |
+-----|-----+
|
+------|-----+
| Transforms |
+------|-----+
|
+-------------------------------------|------------------------------------+
| Writer |
| |
| +--------------+ +-------------+ +-------------+ +------------+ |
| | SPIRV-Writer | | WGSL-Writer | | HLSL-Writer | | MSL-Writer | |
| +-------|------+ +------|------+ +------|------+ +------|-----+ |
+---------|------------------|------------------|------------------|-------+
| | | |
+----|---+ +---|--+ +---|--+ +--|--+
| SPIR-V | | WGSL | | HLSL | | MSL |
+--------+ +------+ +------+ +-----+
The WGSL reader is a recursive descent parser. It closely follows the WGSL grammar in the naming of the parse methods.
The Abstract Syntax Tree is a directed acyclic graph of nodes encoding the structure of the WGSL program.
Many AST nodes have numeric parameters. 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.
After creating the AST for the whole WGSL program, Tint will run an IsValid method which verifies that the produced AST is structurally correct. This means that things like if statements have a condition and body attached.
A later phase of processing, Validation, will check properties such as whether array strides satisfy all the requirements in the WGSL specification.
The type determination stage assigns a result type to each node in the AST. It will do the minimal amount of validation required in order to always be accessing valid nodes, but that doesn't mean the overall AST is valid. (e.g. a 4 component vector type constructor with 5 components will pass type determination but is invalid.)
After the validation step the AST should be a known valid WGSL program.
The inspectors job is to go through the AST 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.
There maybe various transforms we want to run over the AST. This is for things like Vertex Pulling or Robust Buffer Access. These transforms will modify the AST and must produce valid AST after their execution.
Currently the transforms are run individually but we should consider adding a transform manager to maintain and execute the list of transforms.
The writers should be thread safe, we maybe generating the HLSL and MLS output at the same time on different threads. (The writer portion is the only one that needs to be thread safe.)