Slidotron_16x9
Build a ready-to-use horizontal slide-reveal rig in one click — two nested 4K comps, mirrored alpha mattes, and a single 0–100 "CTRL" slider that plays the transition.
Category: composition · Version: 2.0.1 · UI: HEADLESS (no dialog)
What it does
Slidotron 16x9 gives you a complete horizontal slider/gallery transition without building a single mask by hand. Select a composition, run the script, and it creates two nested 4K (3840×2160, 60 fps) comps — "Sliders 16x9" and "Slide 16x9" — wires them together with two mirrored rectangular alpha mattes, and drops a "Sliders 16x9" layer carrying a Slider Control effect named "CTRL" into your original comp. Drag that one slider from 0 to 100 and the two matte panels slide in from opposite edges, progressively revealing whatever artwork you place in "Slide 16x9".
The mechanism is a classic two-panel reveal: "Mask L" and "Mask R" are hidden shape layers, each holding a half-width (1920×2160) rectangle on opposite sides of frame. Two instances of "Slide 16x9" are alpha-matted by — and parented to — those masks, so the visible slice of your content physically travels with the mask edge revealing it. Expressions on each mask's X position remap the CTRL value into screen-space offsets.
Your only remaining job: put content in "Slide 16x9" and animate the slider.
Controls & options
There is no dialog. The control surface is what the script builds — and the expressions look these up by name, so don't rename them:
| Item | Location | Default | Purpose |
|---|---|---|---|
| "CTRL" slider (Slider Control effect) | On the "Sliders 16x9" layer in your original comp | 116 (effectively 100 — the expression clamps to 0–100) | The one control: drives both masks' horizontal position. Usable range 0–100. |
| "Mask L" / "Mask R" shape layers | Inside "Sliders 16x9" | Hidden (eye off) | Alpha-matte sources for the two slide instances. Leave disabled. |
| "Slide 16x9" comp | Project panel | Empty, 3840×2160 @ 60 fps | Put your slide/gallery artwork here. Used twice, once per mask. |
| "Sliders 16x9" comp | Project panel | 4 layers (2 masks + 2 slide instances) | The whole rig; this comp is the layer added to your original composition. |
Name binding: each mask's expression reads comp("<your comp>").layer("Sliders 16x9").effect("CTRL")("Slider"). Renaming the "Sliders 16x9" layer or the "CTRL" effect afterward breaks the rig (expression error). Renaming your original comp is safe — its name is read fresh and escaped when the script runs.
Usage
- Select an existing composition — it becomes the host for the rig.
- Run the script. No dialog appears; the rig is built immediately.
- Open "Slide 16x9" and add your slide/gallery artwork.
- Back in your original comp, select the "Sliders 16x9" layer and keyframe its CTRL slider from 0 to 100 to play the reveal. Reset it to 0 first — the script leaves it at 116, which reads as "fully open".
- Only re-enable "Mask L"/"Mask R" if you need to debug the matte shapes; leave them off for normal use.
Notes
- The slider starts at 116, outside the 0–100 range the expressions map;
linear()clamps it, so the rig first appears in the fully-transitioned position until you set the slider to 0. - Both generated comps are 600 s (10 min) long at 60 fps with a dark-gray (38,38,38) background — trim to taste.
- Running the script again doesn't error: AE auto-suffixes the duplicate comp names ("Sliders 16x9 2"), and the new rig's expressions point at whatever comp was active on that run, so rigs don't cross-reference.
- The whole build is one "Slidotron 16x9" undo group.
Requirements & edge cases
- After Effects 23.0 (2023) or later. The rig is wired with
AVLayer.setTrackMatte(), which doesn't exist before AE 23.0. Unlike the 9x16 sibling script, this version has no runtime version check — on older hosts it errors mid-build with a partial rig, so don't run it there. - A composition must be selected/active before running; otherwise it alerts "Please select a composition first" and exits cleanly.
- The generated expressions have no try/catch — renaming the "Sliders 16x9" layer or "CTRL" effect surfaces as an AE expression error on the mask position properties.
How it works
The script is a single top-level try { beginUndoGroup; compCode_…(); endUndoGroup } catch { alert } block; the timestamped function name is a leftover from the "compCode" recorder tool used to capture a hand-built template (which is also why the geometry constants are long recorded decimals rather than round numbers).
After the comp guard, it creates the two 4K comps with app.project.items.addComp(), adds "Sliders 16x9" as a layer in your original comp, and gives it an ADBE Slider Control renamed "CTRL". Inside "Sliders 16x9" it builds each mask shape layer property-group by property-group — vector group, 1920×2160 rect, zero-width stroke, black fill — then separates Position dimensions to expose ADBE Position_0 as the driven X channel. Mask L gets Scale [-100, 100, 100]: the same rectangle geometry, horizontally flipped, serves as the mirror-image left panel.
Two "Slide 16x9" layer instances get setTrackMatte(mask, TrackMatteType.ALPHA) and are parented to their masks. Finally, each mask's X position receives a linear(CTRL, 0, 100, oMin, oMax) expression (Mask L maps to −5→1920, Mask R to 3840→1920), with your comp's name escaped into the comp("…") reference so quotes and backslashes in comp names can't break it.