src/tint/api/common/resource_binding_config.h

// Copyright 2025 The Dawn & Tint Authors
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#ifndef SRC_TINT_API_COMMON_RESOURCE_BINDING_CONFIG_H_
#define SRC_TINT_API_COMMON_RESOURCE_BINDING_CONFIG_H_

#include <unordered_map>
#include <vector>

#include "src/tint/api/common/binding_point.h"
#include "src/tint/api/common/resource_type.h"
#include "src/tint/utils/reflection.h"

namespace tint {

/// Binding information for a `resource_binding`
struct ResourceBindingInfo {
    // The binding point for the supporting storage buffer. This is a post-remapping binding point.
    BindingPoint storage_buffer_binding;

    // The ordering of default bindings which are placed after the user bindings. These will be used
    // as the index to lookup the given `ResourceType` if the user accesses with an incorrect
    // texture type (or out of bounds).
    //
    // These `default_binding_type_order` entries will be used when we need to substitute in a
    // default binding. So, we assume that Dawn is providing the `resource_binding` memory as:
    //
    // `[user 1 (2d_i32), user 2 (3d_f32), user 3 (1d_u32), 1d_u32_default, 2d_f32_default,
    //  3d_f32_default]`
    //
    // We would then have `default_binding_type_order` entries of:
    //
    // `[1d_u32, 2d_f32, 3d_f32]`
    //
    // Then when we compile a `getBinding<T>(ary, i)` call, we will have created the storage buffer,
    // call it `metadata` in this case:
    //
    // ```
    // const len = metadata.array_length;
    // if (i < len && type_to_u32(T) == metadata.bindings[i]) {
    //   return bindings[i];
    // }
    // return bindings[len + index_in_binding_order(T)];
    // ```
    //
    std::vector<ResourceType> default_binding_type_order;

    TINT_REFLECT(ResourceBindingInfo, storage_buffer_binding, default_binding_type_order);
};

// Configuration for the resource binding transform.
//
// The resource binding transform assumes that for each resource_binding there will be an
// entry in the `bindings` hash map. That binding will provide information on the storage buffer
// attached for the resource binding. Specifically, the storage buffer should have a format of:
//
// ```
// struct SB {
//   array_length: u32,
//   bindings: array<u32>,  // Has `array_length` entries (doesn't include the default bindings).
// }
// ```
//
// The values used in the `bindings` are from the `u32` conversion of the `ResourceType` enum
// entries.
//
struct ResourceBindingConfig {
    /// Map from a `resource_binding` binding point to the supporting info structure.
    std::unordered_map<BindingPoint, ResourceBindingInfo> bindings;

    TINT_REFLECT(ResourceBindingConfig, bindings);
};

}  // namespace tint

#endif  // SRC_TINT_API_COMMON_RESOURCE_BINDING_CONFIG_H_