VertexAccess.h

//
//  VertexAccess.h
//  avara3d
//
//  Created by Morgan Davis on 1/5/26.
//  Copyright © 2026 Morgan K Davis. All rights reserved.
//
 
#ifndef AVARA3D_MESH_VERTEXACCESS_H
#define AVARA3D_MESH_VERTEXACCESS_H
 
#include <cstddef>
#include <cstdint>
#include <optional>
#include <span>
 
#include "a3d/Math.h"
#include "a3d/mesh/VertexLayout.h"
#include "a3d/mesh/VertexLayoutDesc.h"
 
namespace a3d {
 
    class MeshElement;
 
    struct VertexStreamView {
        const std::byte* base   = nullptr;
        uint32_t         count  = 0;
        uint16_t         offset = 0; // attribute offset
        VertexLayout     layout = VertexLayout::None;
    };
 
    inline uint16_t VertexStreamStride(const VertexStreamView& v) {
        return GetVertexLayoutDesc(v.layout).stride;
    }
 
    inline const std::byte* VertexBaseAt(const VertexStreamView& v, uint32_t i) {
        return v.base + std::size_t(i) * std::size_t(VertexStreamStride(v));
    }
 
    struct VertexAccess {
 
        static const VertexAttribDesc* FindAttrib(const VertexLayoutDesc& desc, VertexSemantic semantic);
        static const VertexAttribDesc* GetPositionAttribF32x3(VertexLayout layout);
        static math::vec3              ReadVec3(const std::byte* base, uint16_t offset);
        static void                    WriteVec3(std::byte* base, uint16_t offset, const math::vec3& vec);
        static std::optional<VertexStreamView> GetStreamView(const MeshElement& element,
                                                             VertexSemantic     semantic,
                                                             VertexAttribFormat expectedFormat);
 
        static std::optional<VertexStreamView> GetPositionStreamView(const MeshElement& element);
    };
 
}
 
#endif // AVARA3D_MESH_VERTEXACCESS_H