Track 2 — Motion

Every knob in this track answers the same question: where does the previous frame get redrawn? You already know zoom. Here are the rest, one at a time on the bench, then combined, then read in the wild.

Lesson 1 · zoom, pushed harder

zoom=1.04

▶ Run the tunnel rush

At 4% per frame the compounding stops being subtle: this is the classic flying-through-a-tunnel move. Above 1 flies outward, below 1 falls inward, and the distance from 1 is speed. Almost every preset keeps it within 0.9–1.1; the drama comes from changing it (as in Lesson 4 of Track 1), not from large constants.

Lesson 2 · rot and the pivot

zoom=1.01
rot=0.02

▶ Run the spiral

rot rotates the previous frame by a fixed angle (in radians) each frame. On its own it smears history into rings. Combined with outward zoom it makes the signature MilkDrop move: the spiral — every trail is simultaneously growing and turning.

Rotation happens around the pivot cx, cy (screen fractions; 0.5,0.5 is dead center):

cx=0.3
cy=0.35

▶ Run the off-center spiral

Moving the pivot breaks the symmetry — the vortex leans, and trails on the far side travel farther per frame than trails near the pivot. Run both and watch how different the same rot feels.

Lesson 3 · dx, dy — the push

dx=0.003
dy=-0.002

▶ Run the drift

dx/dy slide the whole previous frame sideways each frame, in screen fractions. Run it and note which way the image travels versus the signs — the vertical axis in particular will surprise you once here so it never surprises you again. Constant small values give wind; audio-driven values (Track 3) give shoves on the beat.

Lesson 4 · sx, sy — the stretch

sx=1.02
sy=0.98

▶ Run the stretch

Per-axis scaling: this pair widens history 2% per frame while squashing it vertically. It's zoom with an opinion about direction — good for flames (stretch up), water (stretch sideways), and funhouse smears.

Lesson 5 · warp — the wobble

warp=0.2
fWarpAnimSpeed=1
fWarpScale=1.5

▶ Run the wobble

warp displaces the previous frame through a built-in animated noise field — instant liquid. fWarpAnimSpeed sets how fast the field churns, and fWarpScale how large its blobs are.

The classic beginner trap: warp=1 plus high decay turns everything into brown smudge within seconds — the noise field stirs the paint and nothing erases it. Experienced authors keep warp low or zero and build distortion with per-pixel equations instead, where they control the field. The anti-pattern table has the full list.

Lesson 6 · Combining knobs

One knob is a demo; a preset is a negotiation between several. This one uses everything from this track plus a per_frame block:

fDecay=0.97
zoom=1.008
per_frame_1=rot = 0.008 + 0.004*sin(time*0.13);
per_frame_2=wave_r = wave_r + 0.25*(0.6*sin(0.98*time) + 0.4*sin(1.047*time));
per_frame_3=wave_g = wave_g + 0.25*(0.6*sin(0.835*time) + 0.4*sin(1.081*time));
per_frame_4=wave_b = wave_b + 0.25*(0.6*sin(0.814*time) + 0.4*sin(1.011*time));

▶ Run the gentle vortex

Line by line:

• per_frame_1 — the spiral's twist is not constant: it drifts between 0.004 and 0.012 on a slow sine (time*0.13 ≈ one swing per 48 s). The motion never settles, so the eye never files it away.
• per_frame_2–4 — each color channel wanders on a sum of two sines at unrelated frequencies (0.98 vs 1.047, …). Irrational-ratio frequencies never realign, so the palette never repeats. This is color cycling with irrational frequencies — Pattern 5 in the coding guide, and a Geiss signature you'll see next.

Turn one knob. Make the vortex violent: shorten decay, raise the rot swing, and speed up the color sines. Then make it glacial. The same six lines cover the whole mood spectrum.

Lesson 7 · Dissection: Geiss — Happy Drops (Ryan Geiss)

Time to read a real one. This ships in the Stims catalog and is old enough to drink. Its six per_frame lines are pure Track 2 material; its three per_pixel lines are a preview of Tracks 3 and 4.

▶ Open Happy Drops in the editor · Watch it in the app

The lines that matter (the rest of the file is default housekeeping):

fDecay=0.98
warp=0.298816
rot=0
wave_r=0.65
wave_g=0.65
wave_b=0.65
per_frame_1=wave_r = wave_r + 0.350*( 0.60*sin(0.742*time) + 0.40*sin(1.021*time) );
per_frame_2=wave_g = wave_g + 0.350*( 0.60*sin(0.703*time) + 0.40*sin(0.969*time) );
per_frame_3=wave_b = wave_b + 0.350*( 0.60*sin(1.090*time) + 0.40*sin(0.963*time) );
per_frame_4=rot = rot + 0.040*( 0.60*sin(0.381*time) + 0.40*sin(0.279*time) );
per_frame_5=cx = cx + 0.110*( 0.60*sin(0.374*time) + 0.40*sin(0.294*time) );
per_frame_6=cy = cy + 0.110*( 0.60*sin(0.393*time) + 0.40*sin(0.223*time) );
per_pixel_1=dr = 0.01 + 0.03*min(max(bass_att-1,0.0), 0.5)*sin(rad*15);
per_pixel_2=dx = dx + dr*cos(ang)*0.75;
per_pixel_3=dy = dy + dr*sin(-ang);

• per_frame_1–per_frame_3 — Lesson 6's irrational-frequency color drift at full strength. Each channel swings 0.35 either side of a neutral 0.65, so red, green, and blue each wander between 0.3 and 1.0 on their own unrelated sines, and the palette never repeats.
• per_frame_4 — the same two-sine trick applied to motion. The file's base rot is 0, so the twist wanders between -0.04 and 0.04: at its peak twice your spiral's 0.02, but it keeps reversing (each sine takes 16–23 seconds per cycle), so it never settles into a plain spiral.
• per_frame_5/per_frame_6 — the pivot from Lesson 2, set wandering. cx and cy each drift up to 0.11 from center, so the point the rotation turns around slides slowly around the middle of the screen.
• per_pixel_1–per_pixel_3 — the preview. These lines run per mesh point, and rad/ang are each point's distance and direction from the screen center. dr pushes every point about 0.01 outward along its own radial line each frame — a steady outward stream, like a gentle zoom. On top of that, bass_att-1 is how far the bass sits above its average, clamped to 0–0.5: in quiet passages it is zero, but on a bass hit sin(rad*15) adds alternating bands of stronger and weaker push across the radius. Those bands, smeared outward by the feedback loop, are the drops. Track 3 covers bass_att; making knobs vary across the screen is all of Track 4.

Exercise. Remix Happy Drops (Remix in the editor's ⋯ menu preserves the credit lineage): cool the palette by lowering the base wave_r to 0.3 and its swing to 0.15, give rot a base of 0.05 so the twist keeps one direction, and turn the stream inward by changing 0.01 to -0.01 in per_pixel_1. Export it, or copy the URL — the link is the preset.

What you can now read

Most of the pre-2007 classics keep their motion in per_frame, and any preset that does is now legible to you: find the knobs, find the sines driving them, find the eraser.

Next: Track 3 — Listening, where sin(time) gives way to the music.