void copy_from(buffer& source)
{
source.unmap();
source.bind();
GL(glBindTexture(GL_TEXTURE_2D, id_));
GL(glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, width_, height_, FORMAT[stride_], TYPE[stride_], NULL));
GL(glBindTexture(GL_TEXTURE_2D, 0));
source.unbind();
source.map(); // Just map it back since map will orphan buffer.
}
