fast_tex_to_px.cpp

// .h
ofBufferObject pixelBufferBack, pixelBufferFront;

// on setup
pixelBufferBack.allocate(3840 * 2160 * 4, GL_DYNAMIC_READ);
pixelBufferFront.allocate(3840 * 2160 * 4, GL_DYNAMIC_READ);

// func
void fast_tex_to_px(ofTexture& tex)
{
	ofPixels pix2;
	tex.copyTo(pixelBufferBack);
	pixelBufferFront.bind(GL_PIXEL_UNPACK_BUFFER);
	unsigned char * p = pixelBufferFront.map<unsigned char>(GL_READ_ONLY);
	pix2.setFromExternalPixels(p, tex.getWidth(), tex.getHeight(), OF_PIXELS_RGBA);
	pixelBufferFront.unmap();
	pixelBufferFront.unbind(GL_PIXEL_UNPACK_BUFFER);
	swap(pixelBufferBack, pixelBufferFront);
}