src/transform/emit_vertex_point_size.cc

// Copyright 2020 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/transform/emit_vertex_point_size.h"

#include <memory>
#include <utility>

#include "src/ast/assignment_statement.h"
#include "src/ast/block_statement.h"
#include "src/ast/float_literal.h"
#include "src/ast/identifier_expression.h"
#include "src/ast/scalar_constructor_expression.h"
#include "src/ast/type/f32_type.h"
#include "src/ast/type_manager.h"
#include "src/ast/variable.h"

namespace tint {
namespace transform {
namespace {

const char kPointSizeVar[] = "tint_pointsize";

}  // namespace

EmitVertexPointSize::EmitVertexPointSize() = default;
EmitVertexPointSize::~EmitVertexPointSize() = default;

Transform::Output EmitVertexPointSize::Run(ast::Module* in) {
  Output out;
  out.module = in->Clone();
  auto* mod = &out.module;

  if (!mod->HasStage(ast::PipelineStage::kVertex)) {
    // If the module doesn't have any vertex stages, then there's nothing to do.
    return out;
  }

  auto* f32 = mod->create<ast::type::F32>();

  // Declare the pointsize builtin output variable.
  auto* pointsize_var =
      mod->create<ast::Variable>(Source{},                    // source
                                 kPointSizeVar,               // name
                                 ast::StorageClass::kOutput,  // storage_class
                                 f32,                         // type
                                 false,                       // is_const
                                 nullptr,                     // constructor
                                 ast::VariableDecorationList{
                                     // decorations
                                     mod->create<ast::BuiltinDecoration>(
                                         ast::Builtin::kPointSize, Source{}),
                                 });
  mod->AddGlobalVariable(pointsize_var);

  // Build the AST expression & statement for assigning pointsize one.
  auto* one = mod->create<ast::ScalarConstructorExpression>(
      Source{}, mod->create<ast::FloatLiteral>(Source{}, f32, 1.0f));
  auto* pointsize_ident = mod->create<ast::IdentifierExpression>(
      Source{}, mod->RegisterSymbol(kPointSizeVar), kPointSizeVar);
  auto* pointsize_assign =
      mod->create<ast::AssignmentStatement>(Source{}, pointsize_ident, one);

  // Add the pointsize assignment statement to the front of all vertex stages.
  for (auto* func : mod->functions()) {
    if (func->pipeline_stage() == ast::PipelineStage::kVertex) {
      func->body()->insert(0, pointsize_assign);
    }
  }

  return out;
}

}  // namespace transform
}  // namespace tint