VertexBufferManager.h

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/* Copyright (C) 2022 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

/*
 * Allocate and destroy CVertexBuffers
 */

#ifndef INCLUDED_VERTEXBUFFERMANAGER
#define INCLUDED_VERTEXBUFFERMANAGER

#include "lib/types.h"
#include "renderer/VertexBuffer.h"

#include <memory>
#include <utility>
#include <vector>

// CVertexBufferManager: owner object for CVertexBuffer objects; acts as
// 'front end' for their allocation and destruction
class CVertexBufferManager
{
public:
    enum class Group : u32
    {
        DEFAULT,
        TERRAIN,
        WATER,
        COUNT
    };

    // Helper for automatic VBChunk lifetime management.
    class Handle
    {
    public:
        Handle() = default;
        Handle(const Handle&) = delete;
        Handle& operator=(const Handle&) = delete;

        explicit Handle(CVertexBuffer::VBChunk* chunk);
        Handle(Handle&& other);
        Handle& operator=(Handle&& other);

        ~Handle() { Reset(); }

        bool IsValid() const { return m_Chunk != nullptr; }
        explicit operator bool() const { return IsValid(); }
        bool operator!() const { return !static_cast<bool>(*this); }
        void Reset();

        friend void swap(Handle& lhs, Handle& rhs)
        {
            using std::swap;

            swap(lhs.m_Chunk, rhs.m_Chunk);
        }

        CVertexBuffer::VBChunk& operator*() const { return *m_Chunk; }
        CVertexBuffer::VBChunk* operator->() const { return m_Chunk; }
        CVertexBuffer::VBChunk* Get() const { return m_Chunk; }

    private:
        CVertexBuffer::VBChunk* m_Chunk = nullptr;
    };

    /**
     * Try to allocate a vertex buffer of the given size and type.
     *
     * @param vertexSize size of each vertex in the buffer
     * @param numberOfVertices number of vertices in the buffer
     * @param type buffer type
     * @param dynamic will be buffer updated frequently or not
     * @param backingStore if not dynamic, this is nullptr; else for dynamic,
     *            this must be a copy of the vertex data that remains valid for the
     *            lifetime of the VBChunk
     * @return chunk, or empty handle if no free chunks available
     */
    Handle AllocateChunk(
        const size_t vertexSize, const size_t numberOfVertices,
        const Renderer::Backend::IBuffer::Type type,
        const bool dynamic, void* backingStore = nullptr, Group group = Group::DEFAULT);

    /// Returns the given @p chunk to its owning buffer
    void Release(CVertexBuffer::VBChunk* chunk);

    size_t GetBytesReserved() const;
    size_t GetBytesAllocated() const;

    /// Explicit shutdown of the vertex buffer subsystem; releases all currently-allocated buffers.
    void Shutdown();

private:

    /// List of all known vertex buffers
    std::vector<std::unique_ptr<CVertexBuffer>> m_Buffers[static_cast<std::size_t>(Group::COUNT)];
};

extern CVertexBufferManager g_VBMan;

#endif