VectorPaint accordion strips: maintain alternating folds and panel continuity

English translation of the Chinese original, translated on 2026-11-06. Original publication dates, attribution, code and version notes are retained.

An accordion strip needs continuity across folds; shading cannot replace structure. Build an original four-panel, three-fold diagram distinguishing perimeter, internal creases and mountain/valley conventions, then draw a more compressed state. This simulates neither paper motion nor exact fold angles and provides no automatic origami or fabrication paths.

Define four panels, three creases and the viewpoint

On an 1100 by 700 pixel canvas, place four panels A–D left to right with only three internal creases, numbered 1–3. Outer left/right edges are not extra folds. Define an oblique view of an upright folded strip with consistent up/down orientation. Sketch a zigzag top and corresponding bottom translated downward by the same amount. This is a checkable static composition, not a calculation of physical fold angles or height from screen geometry.

Connect adjacent quadrilaterals through shared vertices

Use top x positions 100,250,400,550,700 pixels with y alternating 250,200,250,200,250. Translate each bottom point downward 200 pixels and close panels between neighbouring pairs. Check coincident common edges without white seams. These numbers are illustration choices, not exact perspective projections of physical panels. Coincident-looking vertices may not be linked, so editing one requires checking both neighbouring faces instead of expecting automatic following.

State mountain/valley conventions before shading

Label creases mountain, valley, mountain from the explicitly defined viewing side; the other side needs a renewed explanation. Colour alone does not establish fold identity. Inspect equal pale fills to distinguish creases from perimeter, then add restrained alternating values without making panels look like disconnected cards. A physical paper mockup needs orientation-specific folding checks; this screen diagram is not a verified production pattern. Preserve numbered creases before decoration can obscure the convention.

Avoid doubled strokes on creases and perimeter

Inspect stroke sources where neighbouring panels double a shared edge, then retain one crease treatment or reduce duplication. Uniformly thinner strokes do not repair local double lines. Top and bottom turns must meet the same crease endpoints rather than offsetting half a panel. Hide colour and trace creases 1–3, excluding extra verticals that split a face. Hand-drawn references remain artwork to hide as appropriate; check native-grid/guide output separately rather than treating them as structure.

Change the illustrated opening relationship for a compressed state

In a separate copy, change horizontal top-point intervals from 150 to 100 pixels while retaining five boundaries and matching bottom points for a compressed illustration. Panel count and crease IDs remain unchanged; audit each connection. Narrower projection does not mean shorter paper, and this does not calculate the 3D angles preserving physical face width. Label it a state schematic rather than claiming horizontal scaling simulates folding. Keep equal canvas sizes and record manual adjustments; physical production requires a separate mockup.

Join artwork across faces before handling occlusion

For a spanning decorative line, record its face positions in an unfolded source and arrange segments in the current illustration. Keep continuity at folds rather than jumping heights. Use short independent face IDs instead of stretching one flat sentence across four panels and calling it true perspective text. Retain full artwork behind occlusion in the compressed view rather than deleting invisible areas arbitrarily. Establish the undecorated framework first and hide decoration when needed to inspect creases; it does not prove depth relationships.

Keep sources and inspect the narrowest panel in output

Save five-point references, four-panel baseline and both states. In exports, count panels/creases and inspect narrow areas, seams and labels. Check transparent output on another background; white patches do not become holes. Name accordion schematic, state and revision and reopen it to exclude test coordinates or duplicate faces. Explain independent adjoining paths for editable delivery. A paper sample needs separate dimensions, folding and joining decisions; this provides no material-thickness or safety guarantee. Two static states imply neither automatic articulation nor animation.

Trace displaced creases back to shared points

For five apparent panels, inspect outer-edge counting and duplicate objects rather than deleting colour to force four. Compare top/bottom endpoints of one crease for misalignment instead of moving labels. If values conflict with mountain/valley labels, return to viewing side and convention before reversing colours. Repair interrupted artwork through its cross-face source rather than thick cover lines. Recheck four panels, three creases, five boundaries and state explanations so each connection is accountable, not merely a row of unrelated alternating trapezoids.