Summary

Like code . opens VS Code with the current directory, gerbv . should open all recognized gerber/drill/PnP files from a directory. Currently gerbv treats . as a filename, which fails.

Changes

• src/gerbv.c — Add gerbv_is_loadable_file() content probe that runs the same four detection functions used by gerbv_open_image (RS-274X, Excellon, PnP, RS-274D)
• src/gerbv.h — Declare gerbv_is_loadable_file()
• src/main.c — Add scan_directory() helper and modify the CLI file-loading loop to handle directory arguments

How it works

When a CLI argument is a directory, scan_directory() iterates its entries, probes each regular file with gerbv_is_loadable_file(), and collects matches into a sorted list. The probe reuses the exact same detection functions as gerbv_open_image — no extension guessing. This handles extensionless files and dot-prefixed files like .GBL, .GTL (Altium output) since detection is purely content-based.

Usage

Export mode

Directory arguments work with --export too. All files from the directory are loaded as layers and composited into a single output image, exactly as if each file had been listed individually:

# These are equivalent:
gerbv --export=png -o board.png ./gerbers/
gerbv --export=png -o board.png gerbers/copper.gbr gerbers/mask.gbr gerbers/drill.drl

The output is one image with all layers stacked and color-coded — the same view you'd see in the GUI.

Design decisions

• Content-based, not extension-based — gerber files have inconsistent naming across EDA tools (Altium, KiCad, Eagle all differ). Probing file contents is the only reliable detection method.
• Not recursive — only scans the specified directory, not subdirectories. This matches the code . convention and avoids surprises with nested output directories.
• No hidden-file filter — some gerber files are dot-prefixed with no basename (e.g. .GBL). Since every file is content-probed, non-gerber files are silently skipped regardless of name.
• Alphabetical ordering — files are sorted case-insensitively for predictable layer ordering.

Closes #308

Test plan

• cmake --build build — clean build, zero warnings
• ctest — 94/104 pass (unchanged from baseline)
• gerbv test/inputs/ — loads all test gerber/drill files
• gerbv . from empty dir — prints "No loadable files found"
• gerbv file.gbr — single file unchanged
• gerbv --export=png -o out.png test/inputs/ — directory works with export