Check this use of summed area tables for smooth font rendering: https://github.com/DavidGuldbrandsen/SummedAreaFont
References:
Franklin C. Crow
Summed-area tables for texture mapping.
In Proceedings of SIGGRAPH, volume 18(3), pages 207–212, 1984.
Paul Viola & Michael Jones
Rapid Object Detection Using a Boosted Cascade of Simple Features.
In Proceedings of IEEE Conf. Computer Vision and Pattern Recognition, pages 511-518, 2001