| name | openscad-check-renders |
| description | Inspect OpenSCAD preview render images for a model and fix geometry mismatches. Use when the user asks to check renders, compare expected versus actual model shape, review preview.iso.png or preview.xy.png, or diagnose visual problems after SCAD changes. |
OpenSCAD Check Renders
Workflow
Numbers first, pixels second: start from the machine-readable render report,
then use images to locate what the numbers flagged.
- Read
<model>.geometry.json (regenerate with npm run render -- models/<folder>
if missing/stale) and check before looking at any image:
minZ ~0 — otherwise the part floats above the build plate (invisible in
previews because of --viewall --autocenter).dims and per-part dims vs README/SCAD parameters.parts count vs the intended number of printed parts; tiny extra parts are
boolean debris, a missing part means a fragment was silently dropped.cgal.warnings — "unknown variable" means geometry silently disappeared;
non-manifold warnings mean broken booleans.expected.mismatches when the model declares expected_dims/expected_parts.
- Open the render images again even if they were opened earlier. After every SCAD
change, assume all PNGs changed:
preview.iso/xy/xz/yz.png — exterior camera views (bbox overlay bottom-left).<model>.cut-x/y/z.png — cross-sections through the bbox middle: use these to
verify wall thickness, pocket depth, internal cavities and clearances. Grid step
is 10 mm; the darker line marks coordinate 0.
- Identify the intended geometry from the README, SCAD parameters, user request, and nearby model context.
- Compare expected geometry against actual render geometry:
- Overall dimensions and orientation.
- Visible missing or extra cutouts.
- Misaligned holes, frames, pins, ribs, lips, or clips.
- Unexpected intersections, floating parts, inverted axes, or wrong Z placement.
When a detail is ambiguous at full size, zoom into the specific PNG region instead
of judging from the overview.
- Trace each visual problem back to the responsible variables/modules in the SCAD file.
- Fix the SCAD with the smallest geometry-preserving change that addresses the mismatch.
- Regenerate renders after each fix with
npm run render -- models/<folder> (or rely on a running npm run watch) and repeat until both the numbers (step 1) and the images match the expected model.
Notes
Prefer measured evidence (geometry.json, cut views with the 10 mm grid) over
impressions from perspective views. Mention any remaining uncertainty when the
expected physical dimensions are not documented.
