You can use the
viz.RENDER_RIGHT and
viz.RENDER_LEFT flags to prevent a node from rendering to a specific eye in stereo. In your example, if you wanted the line to only show up on the left eye, then you would use the following code:
Code:
import viz
viz.go(viz.HMD | viz.STEREO)
viz.startlayer(viz.LINE_LOOP)
viz.vertexcolor(viz.BLUE)
viz.linewidth(1)
viz.vertex(0.2,0.2)
viz.vertex(0.2,0.5)
viz.vertex(0.5,0.5)
viz.vertex(0.5,0.2)
line = viz.endlayer(viz.SCREEN)
line.disable(viz.RENDER_RIGHT)