Engine stage: trails

Modal

Parameter	Default	Range	What it does
trails	0	0 – 1	How much of the previous frame survives into this one; 0 is no trail, near 1 a long smear.
fb_zoom	1	0.9 – 1.1	Scale the accumulation is grown by each second, so held above 1 the trail tunnels outward.
fb_rotate	0	-1 – 1	Turns per second the accumulation is rotated by, about the feedback centre.
fb_dx	0	-1 – 1	Sideways drift of the accumulation, in frame widths per second.
fb_dy	0	-1 – 1	Vertical drift of the accumulation, in frame heights per second.
fb_center_x	0.5	0 – 1	The horizontal point the zoom and the rotation pivot about, in uv.
fb_center_y	0.5	0 – 1	The vertical point the zoom and the rotation pivot about, in uv.
fb_warp	0	0 – 0.5	Amplitude of a swirl added to the feedback sample, so the trail curls rather than sliding.