It should be possible using glScissor:
http://www.opengl.org/documentation/specs/man_pages/hardcopy/GL/html/gl/scissor.html
I do not know enough about DX to know what works in a similar way.
http://www.opengl.org/documentation/specs/man_pages/hardcopy/GL/html/gl/scissor.html
I do not know enough about DX to know what works in a similar way.