Grey is right about the rendering scene to texture and then to screen - that would appear much smoother. You can see this line flickering very clearly if you draw a filled rect without a texture - the edge will flicker from 1 pixel to the other instead of smoothly gliding in between a single pixel. Subpixels are achieved through texture filtering - monitors can't really display stuff in between pixels.
There is another possible 'line issue' that could display a slight portion of the neighbouring texture cell due to texture filtering - this is a different issue than subpixel 'inaccuracy'. This is related to some driver/card implementations and texture clamping.
There is another possible 'line issue' that could display a slight portion of the neighbouring texture cell due to texture filtering - this is a different issue than subpixel 'inaccuracy'. This is related to some driver/card implementations and texture clamping.