Copy vector<GLubyte> buffer to framebuffer - c++

Question

I am trying to avoid using glDrawPixels in my code, so I'm looking for an alternative.
Below is the code I'm using to read the framebuffer contents into a vector<GLubyte>. Now I need code to transfer the vector contents back to the framebuffer. I've tried a dozen different attempts, but no luck.
glReadBuffer(GL_COLOR_ATTACHMENT0);
GLuint copy_tex = 0;
glGenTextures(1, &copy_tex);
vector<GLubyte> tex_buf(4 * win_x * win_y, 0);
glActiveTexture(GL_TEXTURE2);
glBindTexture(GL_TEXTURE_2D, copy_tex);
glCopyTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 0, 0, win_x, win_y, 0);
glGetTexImage(GL_TEXTURE_2D, 0, GL_RGBA, GL_UNSIGNED_BYTE, &tex_buf[0]);
for (size_t i = 0; i < win_x; i++)
{
for (size_t j = 0; j < win_y; j++)
{
size_t index = 4 * (i*win_y + j);
tex_buf[index + 0] = 255;
tex_buf[index + 1] = 127;
tex_buf[index + 2] = 0;
}
}
glDrawPixels(win_x, win_y, GL_RGBA, GL_UNSIGNED_BYTE, &tex_buf[0]);
glDeleteTextures(1, &copy_tex);

Answer 1

glGetTexImage returns a texture image. If you want to write the image back to the texture then you can use glTexSubImage2D:
glDrawPixels(GL_TEXTURE_2D, 0, 0, 0, win_x, win_y, GL_RGBA, GL_UNSIGNED_BYTE, &tex_buf[0]);
If you want to copy a block of pixels from one framebuffer object to another then you can use glBlitFramebuffer. For instance copy from a named framebuffer to the default framebuffer:
glBindFramebuffer(GL_READ_FRAMEBUFFER, my_fbo);
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
glBlitFramebuffer(0, 0, win_x, win_y, 0, 0, window_h, window_w, GL_COLOR_BUFFER_BIT, GL_LINEAR);
window_h, window_w can be different to win_x, win_y and is the size of the default framebuffer.