This is yet another follow-along of Peter Shirley's Ray Tracing in One Weekend series, with a few more bells and whistles such as multithreading and an SDL window. Some parts of the second book were quite opaque, and these articles by Scratchapixel helped a ton:
Usage: rtc [OPTION...]
Another Peter Shirley Ray Tracer clone
-c, --scene=SCENE_NUM Select a scene to render
-d, --maxdepth=MAX_DEPTH The maximum recursion depth when bouncing rays
-f, --file=FILENAME Save to a PNG file instead of viewing it in a
window
-l, --listscenes List available scenes
-r, --res=RESOLUTION Initial screen resolution, e.g. 1280x720
-s, --samples=NUM_SAMPLES Number of samples per pixel
-t, --numthreads=NUM_THREADS Number of threads to use, defaults to 1
-?, --help Give this help list
--usage Give a short usage message
Mandatory or optional arguments to long options are also mandatory or optional
for any corresponding short options.
