rgbSplit() reads the red, green and blue of each pixel from three slightly different places. Each of red, green and blue is an [x, y] offset in game pixels, so a split of one pixel stays one pixel wide however big the canvas is drawn.
Small and still, it is a cheap lens. Large and shaken for a few frames, it is a hit landing. This example keeps green where it was and moves red and blue in opposite directions.
Click to change direction, ↑ ↓ for how far they split and Space to switch it off.