Here’s the diagram of that movement over time again; take a moment to absorb this, because I’ll use several more of these diagrams.
These can be trickier to interpret than you’d expect from something so simple, especially if the eyes are moving, as we’ll see later.
Now let’s look at the output of a display.
Here, a virtual point is moving across the screen while the eyes again remain fixated straight ahead. The point is illuminated at a single location on the display – the same pixel – for a full frame, because pixels only update once a frame. So instead of a smooth x displacement over time, we get stepped motion as the pixel is redrawn each frame.
Here’s an example of that stepped motion.