CMake Ray Tracer

A simple ray tracer written in pure CMake. Inspired by raytracer.hpp. More information can be found at my blog.

Usage

The ray tracer writes its output to stderr, so you can use it with:

cmake -Dimage_width=64 -Dimage_height=64 -Dnum_procs=4 -P CMakeLists.txt 2> image.ppm

Which writes the output to image.ppm. Then use an image viewer capable of opening PPM files (or this) to view.

Alternatively, the ray tracer can directly write PNG files courtesy of @benmcmorran (PowerShell required for now). Use the use_png variable to set the name of the PNG file without the extension. The example below will write output to render.png.

cmake -Dimage_width=64 -Dimage_height=64 -Dnum_procs=4 -Duse_png=render -P CMakeLists.txt

num_procs controls the number of worker processes spawned. It is recommended to set this to a value no greater than the number of cores in your CPU, for maximum performance.

For now, to keep the code simple, you are required to keep image_width, image_height and num_procs as powers of 2, otherwise the image may not be fully formed. If not specified, these arguments default to the values shown above.

Performance

Using cmake 3.19.2 on Linux 5.4 on a i5-10210U (4 cores, 8 threads), running this command:

for X in 1 2 4 8 16 32 64 128 256 512 ; do echo SIZE $X ; time cmake -Dimage_width=$X -Dimage_height=$X -Dnum_procs=8 -P CMakeLists.txt 2> image_size_${X}.ppm  ; done

PowerShell alternative:

1, 2, 4, 8, 16, 32, 64, 128, 256, 512 | foreach {Write-Host $_; (Measure-Command { cmake "-Dimage_width=$_" "-Dimage_height=$_" "-Dnum_procs=$Env:NUMBER_OF_PROCESSORS" -P CMakeLists.txt 2> image_size_$_.ppm }).TotalSeconds}

Figures reported by time command below (reformatted). As usual, the "real" time is the wall clock time. The others are summed on all processors.

size	real	user	sys
1	0,054s	0,130s	0,051s
2	0,035s	0,098s	0,041s
4	0,077s	0,274s	0,018s
8	0,106s	0,460s	0,023s
16	0,367s	1,871s	0,059s
32	1,296s	7,617s	0,132s
64	5,175s	29,455s	0,356s
128	21,093s	2m06,299s	1,566s
256	1m33,395s	9m21,875s	5,999s
512	7m23,094s	45m36,327s	32,588s

Contributing

All contributions (issue, PRs) are welcome. This project is licensed under the MIT license.