OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Copying Pixel Rectangles

To copy pixels between regions of a buffer, or even different framebuffers, use glBlitFramebuffer(). It uses greater pixel filtering during the copy operation, much in the same manner as texture mapping (in fact, the same filtering operations, GL_NEAREST and GL_LINEAR are used during the copy). Additionally, this routine is aware of multisampled buffers and supports copying between different framebuffers (as controlled by framebuffer objects).

void glBlitFramebuffer(GLint srcX0, GLint srcY0, GLint srcX1,                         GLint srcY1, GLint dstX0, GLint dstY0,                         GLint dstX1, GLint dstY1,                         GLbitfield buffers, GLenum filter);

Copies a rectangle of pixel values from one ...