Working With Buffers

In Unreal Engine, buffers are simply containers of bytes that can store raw data using memory offsets. Understanding how to effectively manage these buffers is essential for tasks like serialization, deserialization, and data storage.

Raw C++ Buffer Management

In raw C++, managing buffers and packing data requires manual handling of memory offsets. For example, consider the following code that packs several uint32_t values into a std::vector<std::byte> buffer:

#include <vector>
#include <cstdint>
#include <cstring>  // For std::memcpy

void PackData()
{
    // Buffer to hold the packed data
    std::vector<std::byte> buffer;

    // Example data
    std::vector<uint32_t> data = { 1234, 5678, 91011 };

    // Calculate the total size needed for the buffer
    size_t totalSize = data.size() * sizeof(uint32_t);

    // Resize the buffer to fit the data
    buffer.resize(totalSize);

    // Copy each uint32_t into the buffer
    for (size_t i = 0; i < data.size(); ++i)
    {
        // Calculate the offset in the buffer
        size_t offset = i * sizeof(uint32_t);

        // Use std::memcpy to copy the data
        std::memcpy(buffer.data() + offset, &data[i], sizeof(uint32_t));
    }
}

In this example, the buffer is resized to hold the data, and each uint32_t value is copied into the buffer at the appropriate offset.

Simplified Buffer Management in Unreal Engine

Unreal Engine simplifies this process with its FMemoryReader and FMemoryWriter classes. These classes handle the serialization and deserialization of data, abstracting away manual memory management.

Using FMemoryWriter

To write data to a buffer, use FMemoryWriter:

#include "Serialization/MemoryWriter.h"
#include "Containers/Array.h"

void SerializeData()
{
    int32 SomeInt = 32;
    TArray<uint8> Buffer;

    {
        // Create a memory writer to serialize data
        FMemoryWriter Writer(Buffer, true /*bSerializeAsSingleBlock*/);
        Writer << SomeInt;
    }
}

Using FMemoryReader

To read data from a buffer, use FMemoryReader:

#include "Serialization/MemoryReader.h"
#include "Containers/Array.h"

void DeserializeData()
{
    int32 DeserializedInt = 0;
    TArray<uint8> Buffer; // Assume this buffer has been filled with data

    {
        // Create a memory reader to deserialize data
        FMemoryReader Reader(Buffer, true /*bDeserializeAsSingleBlock*/);
        Reader << DeserializedInt;
    }
}

Explanation

• FMemoryWriter: Writes data to a TArray<uint8> buffer. The bSerializeAsSingleBlock flag optimizes memory usage by serializing the data in one contiguous block.
• FMemoryReader: Reads data from a TArray<uint8> buffer. The bDeserializeAsSingleBlock flag optimizes memory access during deserialization.

These classes simplify the process of packing and unpacking data, allowing you to focus on higher-level functionality without worrying about manual offset calculations.

Conclusion

Whether you’re working with raw C++ or leveraging Unreal Engine’s built-in classes, managing buffers and memory efficiently is crucial for effective data handling. Unreal Engine’s FMemoryReader and FMemoryWriter provide powerful abstractions that streamline these processes, making your development workflow smoother and more robust.