render

Prompt file imported from obhor/gargantua (.claude/commands/render.md). Fill in {{arguments}} before use. Copyright stays with the author.

Render the Kerr black hole from kerr.cpp. One source file, both outputs — do not create separate files for still vs video.

Arguments given: {{arguments}}

Do this:

1. Build if kerr is missing or older than kerr.cpp:

   g++ -std=c++17 -O3 -march=native -fopenmp kerr.cpp -o kerr

2. Pick the mode. If {{arguments}} says "video"/"orbit", do a video. If it says "still"/"image", do a still. If it's empty or unclear, ask with AskUserQuestion:

   • Still image — one frame, ~80 s, fast to check a change
   • Orbit video — camera fly-around, ~20 s/frame, ~1.5 h for 300 frames

3. Still:

   ./kerr                      # -> kerr_hamiltonian.ppm

   Convert to PNG:

   python3 -c "from PIL import Image; Image.open('kerr_hamiltonian.ppm').save('kerr_render.png')"

   (or ffmpeg -i kerr_hamiltonian.ppm kerr_render.png if PIL isn't around)

4. Video (default 300 frames, or the number in {{arguments}}):

   ./kerr orbit <frames>       # -> frames/f_%04d.ppm
   ffmpeg -framerate 30 -i frames/f_%04d.ppm \
          -c:v libx264 -crf 18 -pix_fmt yuv420p -movflags +faststart \
          -y gargantua_orbit.mp4

   Frames are already flipped in code — do not add hflip,vflip or you undo it. Delete frames/ afterward (it's hundreds of MB).

5. Show the result. For a still, Read the PNG so the user sees it. Report the output path and the wall-clock time.