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// Copyright 2024 The Dawn & Tint Authors
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#ifndef SRC_TINT_LANG_WGSL_AST_TRANSFORM_OFFSET_FIRST_INDEX_H_
#define SRC_TINT_LANG_WGSL_AST_TRANSFORM_OFFSET_FIRST_INDEX_H_
#include "src/tint/lang/wgsl/ast/transform/transform.h"
namespace tint::ast::transform {
/// Adds firstVertex/Instance (injected via push constants) to
/// vertex/instance index builtins.
///
/// This transform assumes that the Name and AddBlockAttribute transforms have been run before.
///
/// Some shading languages start vertex and instance numbering at 0,
/// regardless of the firstVertex/firstInstance value specified. This transform
/// adds the value of firstVertex/firstInstance to each builtin. This action is
/// performed by adding a new push constant equal to original builtin +
/// firstVertex/firstInstance to each function that references one of
/// these builtins.
///
/// For D3D, this affects both firstVertex and firstInstance. For OpenGL,
/// it applies to only firstInstance. For this reason, the first_vertex_offset
/// and first_instance_offset are optional, where std::nullopt indicates that
/// no subsitution is to be performed.
///
/// Before:
/// ```
/// @builtin(vertex_index) var<in> vert_idx : u32;
/// @builtin(instance_index) var<in> inst_idx : u32;
/// fn func() -> u32 {
/// return vert_idx * inst_idx;
/// }
/// ```
///
/// After:
/// ```
/// struct PushConstants {
/// first_vertex : u32,
/// first_instance : u32,
/// }
///
/// var<push_constant> push_constants : PushConstants;
///
/// @builtin(vertex_index) var<in> vert_idx : u32;
/// @builtin(instance_index) var<in> inst_idx : u32;
/// fn func() -> u32 {
/// return (vert_idx + push_constants.first_vertex) * (inst_idx +
/// push_constants.first_instance);
/// }
/// ```
///
class OffsetFirstIndex final : public Castable<OffsetFirstIndex, Transform> {
public:
/// Transform configuration options
struct Config final : public Castable<Config, ast::transform::Data> {
/// Constructor
/// @param first_vertex_off Offset of the firstVertex push constant
/// @param first_instance_off Location of the firstInstance push constant
Config(std::optional<int32_t> first_vertex_off, std::optional<int32_t> first_instance_off);
/// Destructor
~Config() override;
/// Offset of the firstVertex push constant
const std::optional<uint32_t> first_vertex_offset;
/// Offset of the firstInstance push constant
const std::optional<uint32_t> first_instance_offset;
};
/// Constructor
OffsetFirstIndex();
/// Destructor
~OffsetFirstIndex() override;
/// @copydoc Transform::Apply
ApplyResult Apply(const Program& program,
const DataMap& inputs,
DataMap& outputs) const override;
};
} // namespace tint::ast::transform
#endif // SRC_TINT_LANG_WGSL_AST_TRANSFORM_OFFSET_FIRST_INDEX_H_