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* Initial support for uniform parameters on entry points
The basic feature this work adds is the ability to define a shader entry point like:
```hlsl
[shader("fragment")]
float4 main(
uniform Texture2D t,
uniform SamplerState s,
float2 uv : UV)
{
return t.Sample(s,uv);
}
```
In this example, the `uniform` keyword is used to mark that the given entry point parameters are *not* varying input/output flowing through the pipeline, but rather uniform shader parameters that should function as if the shader was declared more like:
```hlsl
Texture2D t,
SamplerState s,
[shader("fragment")]
float4 main(
float2 uv : UV)
{
return t.Sample(s,uv);
}
```
Allowing `uniform` parameters on entry points makes it easier to define multiple entry points in one file without accidentally polluting the global scope with shader parameters that only certain entry points care about.
This feature is also more or less a prerequisite for allowing generic type parameters directly on entry point functions, since the main use case for those type parameters is for determining what goes in various `ConstantBuffer`s or `ParameterBlock`s.
There are two main pieces to the implementation.
First, we need to be able to compute appropriate layout information for entry points that include `uniform` parameters.
Second, we need to transform the entry point function to move any `uniform` parameters to be ordinary global-scope shader parameters, to make sure that all other back-end passes don't need to worry about this special case.
The latter piece of the implementation is, relatively speaking, simpler.
The pass in `ir-entry-point-uniforms.{h,cpp}` converts entry point parameters that are determined to be uniform (using the already-computed layout information) into fields of a `struct` type and then declares a global shader parameter based on that `struct` type (and applies already-computed layout information to that parameter).
After that, the remaining IR passes (notably including type legalization) will handle things just as for any other global shader parameter.
The changes to the layout step are more significant, but most of the changes are just cleanups and fixes to enable the feature.
The two major changes that enable entry-point `uniform` parameters are:
* In `collectEntryPointParameters` we now dispatch out to a new `computeEntryPointParameterTypeLayout` function, which decided whether to compute the type layout for a `uniform` parameter, or for a varying parameter (what used to be the default behavior handled by `processEntryPointParameterDecl`).
* The main `generateParameterBindings` routine was extended so that it allocates registers/bindings to the resources required by each entry point (using `completeBindingsForParameter`) after it has allocated registers/binding to all of the global-scope parameters (this addition is mirrored in `specializeProgramLayout`).
The effect of these changes is that the `uniform` parameters of any entry points specified in a compile request will be laid out after the global-scope parameters, in the order the entry points were specified in the compile request.
A bunch of smaller changes were made around parameter layout that are worth enumerating so that the diffs make some sense:
* The `EntryPointLayout` type was changed so that instead of trying to *be* a `StructTypeLayout`, it instead *owns* one, in the same fashion as `ProgramLayout`. This commonality was factored into a base class `ScopeLayout`, and a bunch of edits followed from that change.
* Because `uniform` parameters are moved out of the entry point parameter list early in the IR transformations, the logic in `ir-glsl-legalize.cpp` that tried to look up parameter layout information by index would no longer work if the entry point parameter list had been altered. Instead, that logic now looks for the decorations directly on the parameters.
* The `UsedRange` type in `parameter-binding.cpp` was tracking the existing parameter associated with a range using a `ParameterInfo*` (which accounts for the possibility of multiple `VarDecl`s mapping to the same logical shader parameter), when just using a `VarLayout*` is sufficient for all current use cases. The overhead of allocating a `ParameterInfo` seems like overkill for entry-point parameters, where there can't possibly be multiple declarations of the "same" parameter, so avoiding these overheads was a focus when trying to deduplicate code between the global and entry-point parameter cases.
* A bunch of parameter binding logic that was specific to GLSL input has been deleted completely. There was no way to even execute this code in the compiler today, and there is pretty much zero chance of us needing (or wanting) to deal with GLSL input in the future. This includes custom `UsedRangeSet`s specific to each translation unit, which were only needed for global-scope `in` and `out` varying declarations in GLSL.
* A bunch of functions with `EntryPointParameter` in their names were renamed to use `EntryPointVaryingParameter` to help distinguish that they only apply to the varying case, while entry point `uniform` parameters are handled elsewhere.
* The `completeBindingsForParameter` function was re-worked into something that can be used for both global-scope shader parameters (where we have a `ParameterInfo` and possibly explicit bindings) and entry-point parameters (where we expect to have neither). This helps unify the (fairly subtle) logic for how we allocate and assign bindings for resources, constant buffers, parameter blocks, etc.
* A small change was made so that the entry-point stage is attached directly to top-level parameters of the entry point, and *not* recursively to every field along the way. This could be a breaking change for some applications, but it makes more logical sense (to me); we'll have to check if this affects Falcor. This change produces different output for several of the reflection tests, but the changes are consistent with no longer attaching stage information to sub-fields of varying `struct`-type parameters.
* Because there is a bunch of repeated logic in `parameter-binding.cpp` that has to do with computing a `struct` layout for ordinary/uniform data, I tried to factor that into a single `ScopeLayoutBuilder` type, which handles computing the offsets for any parameters with ordinary data, and then also handles wrapping up the layout in a constant buffer layout if there was any ordinary data at the end.
* A similar convenience routine `maybeAllocateConstantBufferBinding` was added because I noticed multiple places in `parameter-binding.cpp` that were trying to allocate a constant buffer binding for global uniforms, and they were wildly inconsistent (and in most cases used logic that would only work for D3D).
* The main `generateParameterBindings` routine is significantly shortened by using all of these utilities that were introduced. I tried to comment the places that changed to explain the overall flow correctly.
* The `specializeProgramLayout` routine (used to take a `ProgramLayout` from `generateParameterBindings` and specialize it based on knowledge of global generic arguments) had basically been rewritten with more explicit commenting/rationale for what happens in each step. It makes use of the same shared utilities as `generateParameterBindings` and `collectEntryPointParameters`.
In terms of testing:
* I added a test case to specifically test the new behavior, and in particular I made sure to include a mix of both global and entry-point parameters and also to have entry-point parameters of both ordinary and resource/object types.
* I tweaked an existing test for global type parameters to use an entry-point `uniform` parameter instead of a global one, in an effort to migrate it toward being able to use an explicitly generic entry point.
* fixups from merge
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Fixes #301
The problem here is that if you have input GLSL code like:
```glsl
// example.vs
in vec3 pos;
```
and:
```glsl
// example.fs
in vec3 worldPos;
```
Then both `pos` and `worldPos` are reflected as global variables (parameters of the *program*), which both get bound to "varying input" resources, but there is no way to tell through the API that `pos` is a vertex parameter while `worldPos` is a fragment one.
The original request in issue #301 was to expose parameters like this not as a global variables, but rather as parameters of the entry point in their specific file. That is, treat it as if the user had written, e.g.:
```glsl
// example.vs
void vsMain(in vec3 pos) { ... }
```
Doing that would unify the GLSL and HLSL/Slang cases a bit, but would require the Slang reflection API to lie about the structure of code the user wrote. At a more basic level, that would have been hard to implement because the current reflection API just exposes the underlying AST, and the AST *needs* to leave `pos` at the global scope so that when we go and spit GLSL back out we retain the original structure.
This PR implements a more simplistic solution, where the user is allowed to query the stage that a varying parameter "belongs" to. For right now I'm only enabling this to work for varying parameters (but it doesn't care if they are entry-point or global-scope varyings). Despite what I said on #301, this should work for both the top-level parameter's variable layout, *and* any variable layouts for fields within its type reflection.
In terms of implementation, I took the simple but wasteful route: every `VarLayout` now has a `stage` field that is by default initialized to `SLANG_STAGE_NONE`. When collecting varying parameters, I take advantage of the fact that everything bottlenecks through `processEntryPointParameter()` which takes an `EntryPointParameterState` so that I can set the `VarLayout::stage` field for any varying parameter in one place.
While I was making this change, I also did a bit of cleanup so that the "official" names for the varying parameter categories are `VARYING_INPUT` and `VARYING_OUTPUT`, with `VERTEX_INPUT` and `FRAGMENT_OUTPUT` being "deprecated" in principle. I didn't do the bulk rename inside the codebase yet.
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