xmoltoppm 1.0.0

XYZ trajectory to PPM/PNG molecular visualization (Python port of xmoltoppm)

xmoltoppm

Turn XYZ molecular dynamics trajectories into images or movies in one command.

For the full capability set (all options and flags), run xmoltoppm -h or open docs/guide.md (reference-style; detailed options and workflows).

— Publish to PyPI once so the badge and pip install xmoltoppm work.

This package is a Python port of the original Fortran xmoltoppm by Adri C.T. van Duin. See What's new in this version below for updates in this port.

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What it does

xmoltoppm reads XYZ-format trajectory files and draws 2D pictures: atoms as coloured circles, bonds by distance. You get a single snapshot or a numbered sequence of frames ready for video encoding. No interactive prompts—everything is controlled from the command line.

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✨ Features

• Single command to movie: Render every frame (or every Nth) from a trajectory into numbered PPM or PNG files; feed them to ffmpeg and you have a movie.
• One snapshot in seconds: Export the first frame (or any frame) with size, style, and format options in one line.
• Flexible XYZ input: Works with standard 4-column XYZ and with extended formats (e.g. ReaxFF comment line, optional estrain/velocity columns).
• PNG and run metadata: Use --png for PNG output (with Pillow); use --write-run-json to record input path, options, and version for reproducibility.
• Rich styling: Shaded circles, multiple line styles (including directional shadow), strain or velocity coloring, velocity arrows, text and graphics overlays, rotation animation, transparent atoms, config files and presets.

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📦 Installation

Get up and running with pip:

pip install xmoltoppm

Optional PNG support (recommended if you want PNG output):

pip install xmoltoppm[png]
# or
pip install Pillow

Requires Python 3.9+ and NumPy.

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Quick Start

The easiest way to use xmoltoppm:

xmoltoppm -i traj.xyz -o output.ppm
xmoltoppm -i traj.xyz -af 0 -ft 0 -o frames/
xmoltoppm -i traj.xyz --preset movie -af 0 -o movie_frames/

• Line 1: first frame only → one image.
• Line 2: all frames → 0001.ppm, 0002.ppm, … in frames/.
• Line 3: same with pretty defaults (size 800, shaded circles, shadow).

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📖 Practical Examples

Single snapshot

Get one image from the first frame:

xmoltoppm -i traj.xyz -s 500 -cc 1 -il 3 -o snapshot.ppm

For PNG:

xmoltoppm -i traj.xyz -s 500 -cc 1 -il 3 -o snapshot.png --png

Full trajectory to movie frames

Render every frame into numbered files, then encode with ffmpeg:

xmoltoppm -i traj.xyz -s 500 -cc 1 -il 3 -af 0 -ft 0 -o frames/
# Produces frames/0001.ppm, frames/0002.ppm, ...
ffmpeg -framerate 25 -i frames/%04d.ppm -pix_fmt yuv420p movie.mp4

Pretty movie preset and run metadata

Use the built-in “movie” preset and record options for reproducibility:

xmoltoppm -i traj.xyz --preset movie -af 0 -ft 0 -o movie_frames/ --write-run-json

This uses size 800, shaded circles, line style 4 with shadow, and writes a .run.json next to the first output with input path, options, and version.

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Key options

Option	Description
-i, --input	Input XYZ file (required)
-o, --output	Output path or directory base (default: output.ppm)
-s, --size	Canvas size in pixels (default: 500)
-cc	Circle style: 0 flat, 1 shaded
-il	Line style: 0–4 (single/two-colour, shadow, directional)
-af iskip	Output all frames; iskip = frames to skip (0 = every frame)
-ft	Filename type: 0 0001.ppm, 1 1.ppm, 2 molname.ppm
--png	Write PNG instead of PPM (requires Pillow)
--preset movie	Pretty defaults: size 800, shaded, line style 4, shadow
-c, --config	Load options from JSON or YAML file
--max-frames N	Limit to first N frames
--write-run-json	Write sidecar JSON with input, options, version

Run xmoltoppm -h for the full list of options.

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XYZ format

• Line 1: Number of atoms (integer).
• Line 2: Comment. If it has 9 space-separated fields, they are parsed as molname, iteration, energy, cell lengths/angles; otherwise defaults are used.
• Next N lines: One per atom. Minimum: symbol x y z. Optional extra columns: type, estrain, or velocity components.

So any standard XYZ with at least 4 columns per atom works.

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FAQ / Troubleshooting

• “PNG output requires Pillow”
  Install Pillow: pip install Pillow or pip install xmoltoppm[png].

• Does it work with my XYZ file?
  Yes, if each atom line has at least symbol x y z. Extra columns (e.g. type, estrain, velocities) are used when present for coloring, arrows, or vibrational mode.

• No frames written / “no frames read”
  Check that the first line is the atom count (integer) and the next N lines are atom lines. See docs/guide.md for detailed XYZ format.

• Why does shadow seem to move or flip between frames?
  Shadow is view-depth (z) based: “lit” atoms follow which side faces the viewer. As the molecule rotates, the lit side can shift (e.g. top vs bottom). Line style 4 adds a z-based component on bonds; for a fixed world light direction, a future version may add an option.

• Do output images have a fixed size for movies?
  Yes. Every frame is rendered at the same pixel dimensions (square canvas from -s), so ffmpeg and other encoders get a consistent sequence.

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What's new in this version

This port adds the following relative to the original Fortran xmoltoppm:

• Full CLI — No interactive prompts or temp files; all options via arguments.
• PNG and run metadata — --png (with Pillow) and --write-run-json for reproducibility.
• Robust XYZ — Standard 4-column plus optional ReaxFF header and extra columns (estrain, velocities).
• Fixed canvas for movies — Output dimensions stay constant across frames so ffmpeg and other encoders get a consistent sequence.
• Modular code — Separate IO, core, viz, and CLI; tests and extensions are straightforward.

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🤝 Contributing and support

Found a bug or have a question? Open an issue on the project repository. See CONTRIBUTING.md for development setup, tests, and how to add options. For detailed documentation (XYZ format, all options, workflows), see docs/guide.md. See CHANGELOG.md for version history.

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Appendix A: verification — where to look and what to check

After running python scripts/run_ship_verification.py (requires traj.xyz in the project root), outputs go to verification_review/<group>/. A snapshot is also in the repo as verification_review.tar.gz — extract with tar -xzf verification_review.tar.gz. Use this to evaluate accuracy and quality:

Group	Where	What to check
baseline	verification_review/baseline/	102 PPMs; default style; molecule centered, bonds visible; fixed image size every frame.
circle_line_styles_il0 / il3 / il4	…/circle_line_styles_il0/, il3/, il4/	il0: flat circles, single-colour bonds. il3: shaded circles, two-colour + shadow. il4: adds z-based directional component on bonds (may look similar to il3).
shadow / shadow_invert	…/shadow/, …/shadow_invert/	Shadow is view-depth (z) based; as the molecule rotates, lit atoms can shift (top/bottom). shadow_invert flips the bond-direction component.
png_output	…/png_output/	102 PNGs; same content as baseline, PNG format.
overlays_text	…/overlays_text/	Text shows Frame 1, Frame 2, … (output frame number) at fixed position.
overlays_graphics	…/overlays_graphics/	Small inset plot in a fixed corner, not over the atoms.
strain_coloring	…/strain_coloring/	Atoms coloured by estrain; colour gradient vs baseline.
transparent	…/transparent/	Atoms 1–3 outline-only (transparent fill).
rotation_anim	…/rotation_anim/	Frames 0001→0102: molecule rotates 360° around z.
max_frames	…/max_frames/	Exactly 2 frames (0001, 0002).
config_preset	…/config_preset/	Options from sample_config.json.
preset_movie	…/preset_movie/	Size 800, shaded, line style 4, shadow.
recenter	…/recenter/	Molecule re-centred each frame.
supersample	…/supersample/	Sharper (2× render then downscale).
boundary_box	…/boundary_box/	2D frame (0.95× inset rectangle only); view scaled to molecule; no 3D box atoms.
write_run_json	…/write_run_json/	102 PPMs plus 0001.ppm.run.json with input, options, version.

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Appendix B: Example run times

Typical wall times for rendering all frames of a 102-frame trajectory (6 atoms per frame) on a single run:

Scenario	Frames	Wall time (s)
Baseline (default style)	102	~63
PNG output	102	~14
Text overlay	102	~97
Strain coloring	102	~66

Times are from verification_review/timing_report.txt (run python scripts/run_ship_verification.py to regenerate). Your times will depend on trajectory size and hardware.