Space layers 'x' apart, but make sure they land on a whole
pixel

What would be the best way to take a number of layers and make sure they are 'x'
pixels apart (using a slider), but making sure they are positioned on whole
pixels (to avoid the blurry sub-pixel positioning).

Probably the easiest way to force a slider to produce only whole number values
is to add the following expression to the slider. This simplifies the other
expressions that are driven by the slider values.

Math.floor(value);