Realtime heatmap with canvas & js

Couple notes- it's not a true "heatmap" since it only works when the mouse is moving. If I two-finger scroll to another place, it doesn't register that the mouse has been over a new spot until I move it again. Likewise, if I hover over a spot for a long time then quickly move it somewhere else, it doesn't turn red, only registers a small blue dot because the mouse was not moving (only works when mouse is moving).

Then again I think the applications for this tech/visual effect are much wider than an analytical heatmap.