axmol/core/renderer/backend/metal/BufferMTL.h

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 Copyright (c) 2018-2019 Xiamen Yaji Software Co., Ltd.

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#pragma once

#include "../Buffer.h"
#import <Metal/Metal.h>

NS_AX_BACKEND_BEGIN

/**
 * @addtogroup _metal
 * @{
 */

/**
 * @brief Used to store vertex and index data data.
 * Dynamic buffer data refers to frequently updated data stored in a buffer.
 * To avoid creating new buffers per frame and to minimize processor idle time between frames, implement a triple
 * buffering model to update dynamic buffer.
 */
class BufferMTL : public Buffer
{
public:
    /// @name Constructor, Destructor and Initializers
    /**
     * @brief BufferMTL constructor
     * @param mtlDevice The device for which MTLBuffer object was created.
     * @param size Specifies the size in bytes of the buffer object's new data store.
     * @param type Specifies the target buffer object. The symbolic constant must be BufferType::VERTEX or
     * BufferType::INDEX.
     * @param usage Specifies the expected usage pattern of the data store. The symbolic constant must be
     * BufferUsage::STATIC, BufferUsage::DYNAMIC.
     */
    BufferMTL(id<MTLDevice> mtlDevice, std::size_t size, BufferType type, BufferUsage usage);
    ~BufferMTL();

    /// @name Update Buffer
    /**
     * @brief Update buffer data
     * @param data Specifies a pointer to data that will be copied into the data store for initialization.
     * @param size Specifies the size in bytes of the data store region being replaced.
     * @see `updateSubData(void* data, unsigned int offset, unsigned int size)`
     */
    virtual void updateData(void* data, std::size_t size) override;

    /**
     * @brief Update buffer sub-region data
     * @param data Specifies a pointer to the new data that will be copied into the data store.
     * @param offset Specifies the offset into the buffer object's data store where data replacement will begin,
     * measured in bytes.
     * @param size Specifies the size in bytes of the data store region being replaced.
     * @see `updateData(void* data, unsigned int size)`
     */
    virtual void updateSubData(void* data, std::size_t offset, std::size_t size) override;

    /**
     * Emply implementation. Mainly used in EGL context lost.
     */
    virtual void usingDefaultStoredData(bool needDefaultStoredData) override{};

    /// @name Setters & Getters
    id<MTLBuffer> getMTLBuffer() const;

    /**
     * @brief a triple buffering
     * Will switch to next buffer and use the buffer in the following render pass in current frame.
     */
    void beginFrame();

private:
    void updateIndex();

    id<MTLBuffer> _mtlBuffer            = nil;
    NSMutableArray* _dynamicDataBuffers = nil;
    int _currentFrameIndex              = 0;
    bool _indexUpdated                  = false;
};

// end of _metal group
/// @}
NS_AX_BACKEND_END