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// Copyright 2022 The Tint Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "src/tint/transform/clamp_frag_depth.h"
#include <utility>
#include "src/tint/ast/attribute.h"
#include "src/tint/ast/builtin_attribute.h"
#include "src/tint/ast/builtin_value.h"
#include "src/tint/ast/function.h"
#include "src/tint/ast/module.h"
#include "src/tint/ast/struct.h"
#include "src/tint/ast/type.h"
#include "src/tint/program_builder.h"
#include "src/tint/sem/function.h"
#include "src/tint/sem/statement.h"
#include "src/tint/sem/struct.h"
#include "src/tint/utils/scoped_assignment.h"
#include "src/tint/utils/vector.h"
TINT_INSTANTIATE_TYPEINFO(tint::transform::ClampFragDepth);
namespace tint::transform {
namespace {
bool ContainsFragDepth(utils::VectorRef<const ast::Attribute*> attributes) {
for (auto* attribute : attributes) {
if (auto* builtin_attribute = attribute->As<ast::BuiltinAttribute>()) {
if (builtin_attribute->builtin == ast::BuiltinValue::kFragDepth) {
return true;
}
}
}
return false;
}
bool ReturnsFragDepthAsValue(const ast::Function* fn) {
return ContainsFragDepth(fn->return_type_attributes);
}
bool ReturnsFragDepthInStruct(const sem::Info& sem, const ast::Function* fn) {
if (auto* struct_ty = sem.Get(fn)->ReturnType()->As<sem::Struct>()) {
for (auto* member : struct_ty->Members()) {
if (ContainsFragDepth(member->Declaration()->attributes)) {
return true;
}
}
}
return false;
}
bool ShouldRun(const Program* program) {
auto& sem = program->Sem();
for (auto* fn : program->AST().Functions()) {
if (fn->PipelineStage() == ast::PipelineStage::kFragment &&
(ReturnsFragDepthAsValue(fn) || ReturnsFragDepthInStruct(sem, fn))) {
return true;
}
}
return false;
}
} // anonymous namespace
ClampFragDepth::ClampFragDepth() = default;
ClampFragDepth::~ClampFragDepth() = default;
Transform::ApplyResult ClampFragDepth::Apply(const Program* src, const DataMap&, DataMap&) const {
ProgramBuilder b;
CloneContext ctx{&b, src, /* auto_clone_symbols */ true};
// Abort on any use of push constants in the module.
for (auto* global : src->AST().GlobalVariables()) {
if (auto* var = global->As<ast::Var>()) {
if (var->declared_address_space == ast::AddressSpace::kPushConstant) {
TINT_ICE(Transform, b.Diagnostics())
<< "ClampFragDepth doesn't know how to handle module that already use push "
"constants.";
return Program(std::move(b));
}
}
}
if (!ShouldRun(src)) {
return SkipTransform;
}
auto& sem = src->Sem();
auto& sym = src->Symbols();
// At least one entry-point needs clamping. Add the following to the module:
//
// enable chromium_experimental_push_constant;
//
// struct FragDepthClampArgs {
// min : f32,
// max : f32,
// }
// var<push_constant> frag_depth_clamp_args : FragDepthClampArgs;
//
// fn clamp_frag_depth(v : f32) -> f32 {
// return clamp(v, frag_depth_clamp_args.min, frag_depth_clamp_args.max);
// }
b.Enable(ast::Extension::kChromiumExperimentalPushConstant);
b.Structure(b.Symbols().New("FragDepthClampArgs"),
utils::Vector{b.Member("min", b.ty.f32()), b.Member("max", b.ty.f32())});
auto args_sym = b.Symbols().New("frag_depth_clamp_args");
b.GlobalVar(args_sym, b.ty.type_name("FragDepthClampArgs"), ast::AddressSpace::kPushConstant);
auto base_fn_sym = b.Symbols().New("clamp_frag_depth");
b.Func(base_fn_sym, utils::Vector{b.Param("v", b.ty.f32())}, b.ty.f32(),
utils::Vector{b.Return(b.Call("clamp", "v", b.MemberAccessor(args_sym, "min"),
b.MemberAccessor(args_sym, "max")))});
// If true, the currently cloned function returns frag depth directly as a scalar
bool returns_frag_depth_as_value = false;
// If valid, the currently cloned function returns frag depth in a struct
// The symbol is the name of the helper function to apply the depth clamping.
Symbol returns_frag_depth_as_struct_helper;
// Map of io struct to helper function to return the structure with the depth clamping applied.
utils::Hashmap<const ast::Struct*, Symbol, 4u> io_structs_clamp_helpers;
// Register a callback that will be called for each visted AST function.
// This call wraps the cloning of the function's statements, and will assign to
// `returns_frag_depth_as_value` or `returns_frag_depth_as_struct_helper` if the function's
// return value requires depth clamping.
ctx.ReplaceAll([&](const ast::Function* fn) {
if (fn->PipelineStage() != ast::PipelineStage::kFragment) {
return ctx.CloneWithoutTransform(fn);
}
if (ReturnsFragDepthAsValue(fn)) {
TINT_SCOPED_ASSIGNMENT(returns_frag_depth_as_value, true);
return ctx.CloneWithoutTransform(fn);
}
if (ReturnsFragDepthInStruct(sem, fn)) {
// At most once per I/O struct, add the conversion function:
//
// fn clamp_frag_depth_S(s : S) -> S {
// return S(s.first, s.second, clamp_frag_depth(s.frag_depth), s.last);
// }
auto* struct_ty = sem.Get(fn)->ReturnType()->As<sem::Struct>()->Declaration();
auto helper = io_structs_clamp_helpers.GetOrCreate(struct_ty, [&] {
auto* return_ty = fn->return_type;
auto fn_sym = b.Symbols().New("clamp_frag_depth_" +
sym.NameFor(return_ty->As<ast::TypeName>()->name));
utils::Vector<const ast::Expression*, 8u> initializer_args;
for (auto* member : struct_ty->members) {
const ast::Expression* arg = b.MemberAccessor("s", ctx.Clone(member->symbol));
if (ContainsFragDepth(member->attributes)) {
arg = b.Call(base_fn_sym, arg);
}
initializer_args.Push(arg);
}
utils::Vector params{b.Param("s", ctx.Clone(return_ty))};
utils::Vector body{
b.Return(b.Construct(ctx.Clone(return_ty), std::move(initializer_args))),
};
b.Func(fn_sym, params, ctx.Clone(return_ty), body);
return fn_sym;
});
TINT_SCOPED_ASSIGNMENT(returns_frag_depth_as_struct_helper, helper);
return ctx.CloneWithoutTransform(fn);
}
return ctx.CloneWithoutTransform(fn);
});
// Replace the return statements `return expr` with `return clamp_frag_depth(expr)`.
ctx.ReplaceAll([&](const ast::ReturnStatement* stmt) -> const ast::ReturnStatement* {
if (returns_frag_depth_as_value) {
return b.Return(stmt->source, b.Call(base_fn_sym, ctx.Clone(stmt->value)));
}
if (returns_frag_depth_as_struct_helper.IsValid()) {
return b.Return(stmt->source,
b.Call(returns_frag_depth_as_struct_helper, ctx.Clone(stmt->value)));
}
return nullptr;
});
ctx.Clone();
return Program(std::move(b));
}
} // namespace tint::transform