Why a G-code Preview Is Incomplete: Arcs, Macros and Formats

An incomplete preview can come from unsupported motion or state changes, a bounded renderer, unreadable input or malformed text. Those cases need different next actions. Read each metric's coverage instead of treating the picture or number of recognised lines as a machine compatibility score.

Follow a finding to its source

The owned unsupported-arc control first uses common linear commands, then G2 and a custom macro. InspectMesh groups the unsupported findings, retains original first/last line references and up to three bounded samples, and labels subsequent path coverage incomplete. Selecting an excerpt focuses its read-only panel. Only a retained motion line with a reliable mapping selects a preview layer; metadata and commands outside a parsed path have no exact layer association.

Identify the cause before changing the file

Text recognition is not extension recognition

Renaming a binary container to .gcode does not make it plain text. Prusa documents a binary G-code format and native conversion/viewing support; InspectMesh does not decode that format or vendor containers. Import rejects undecodable bytes and control characters. A readable extension still needs successfully parsed instructions. Files are limited to 25 MiB; source lines over 4,096 characters are unavailable to keep parameter processing bounded.

Which metrics can remain useful?

A supported PrusaSlicer 2.9.6 normal-mode duration comment can remain a recognised declaration when an arc makes extents incomplete. It is neither measured elapsed time nor proof that every path was inspected. A missing or ambiguous consumption field remains unavailable, never zero. Multiple tools cannot be silently collapsed into a single spool; unsupported length metadata needs manual interpretation and confirmed diameter/density before mass conversion.

Mode assumptions also matter. G90/G91 after M82/M83 is disclosed as firmware-dependent extrusion classification in the conservative model. G92 E resets logical extrusion without ordinary XYZ movement; G92 XYZ changes the frame and does not prove machine-space bounds.

Reproduce the distinction

1. Load the unsupported-arc, ambiguous-metadata, malformed-number and comments-only analytical controls from Examples.
2. Compare coverage, unavailable offers and original line evidence.
3. Keep JSON/copy/print with their limitations, then open the original job in the appropriate native viewer.

All snippets are hand-authored parser controls, incomplete and unsafe to execute on a printer. No native software screenshots or physical print results are claimed.

Use the existing review tools

Open the read-only G-code viewer, follow the general G-code review procedure, and download the owned analytical controls. Source geometry fit remains in the model-fit guide; arrangement remains in the existing layout guide.

Sources and evidence boundary

Official sources reviewed 10 October 2026: PrusaSlicer G-code viewer, Prusa binary G-code, Marlin G92, Marlin M82, Klipper commands, and Prusa sequential printing. InspectMesh's declarations are bounded file observations; diagrams and snippets are original analytical examples, not machine approval.