How to Avoid OpenGL Errors When Using RAII in C ?

Resolving OpenGL Object Issues in C RAII Classes

Background

In C , RAII (Resource Acquisition Is Initialization) is employed to ensure automatic resource cleanup. When an object goes out of scope, its destructor is called, releasing any resources it holds.

Problem

Consider a C class with an OpenGL object managed through RAII:

class BufferObject {
public:
  BufferObject() { glGenBuffers(1, &buff_); }
  ~BufferObject() { glDeleteBuffers(1, &buff_); }
};

When used in certain scenarios, such as storing in a vector or returning from a function, problems arise with OpenGL errors.

Analysis

The issue stems from the lack of proper copy/move semantics. When copying the object (e.g., push_back), only the member variables are copied, leaving both objects with the same OpenGL buffer object. Upon destruction, the first object deletes the buffer, rendering the second object invalid.

Solution: Implementing Move Semantics

To resolve this, the class should be converted to a move-only type, removing the copy constructor and copy assignment operator. Instead, move constructors and move assignment operators should be provided that transfer ownership of the resource:

class BufferObject {
public:
  BufferObject(const BufferObject &) = delete;
  BufferObject &operator=(const BufferObject &) = delete;

  BufferObject(BufferObject &&other) : buff_(other.buff_) {
    other.buff_ = 0;
  }

  BufferObject &operator=(BufferObject &&other) {
    if (this != &other) {
      Release();
      buff_ = other.buff_;
      other.buff_ = 0;
    }
    return *this;
  }
};

This ensures that only one object owns the OpenGL buffer at any given time.

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