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A light ray marcher built in C
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I C the Light

a distance estimating ray marcher written in C

quaternion julia set rendered with I C the Light

On ray marching (from Syntopia):

Classic raytracing shoots one (or more) rays per pixel and calculates where the rays intersect the geometry in the scene. Normally the geometry is described by a set of primitives, like triangles or spheres, and some kind of spatial acceleration structure is used to quickly identify which primitives intersect the rays.

Distance Estimation, on the other hand, is a ray marching technique.

Instead of calculating the exact intersection between the camera ray and the geometry, you proceed in small steps along the ray and check how close you are to the object you are rendering. When you are closer than a certain threshold, you stop. In order to do this, you must have a function that tells you how close you are to the object: a Distance Estimator. The value of the distance estimator tells you how large a step you are allowed to march along the ray, since you are guaranteed not to hit anything within this radius.

Supplementary information and reference links can be found at



The code lives in source/, as you might expect. The render loop and main() are in icthelight.c.

Images will be written to output/.

Compiling / Running

To compile with SDL, you’ll need a copy of SDL 2.0.4, which can be downloaded here. I don't expect this to change any time in the near future, so don't worry if this gets a bit out of date.

To compile without SDL, comment out #define USE_REAL_SDL in source/sdl.h to add a set of stub functions that let I C the Light compile without error (you will get a bunch of unused function parameter warnings, though). Obviously, a window won’t be created, but writing the images still works fine.

To run, you’ll need a copy of SDL2.dll to live in the same directory as the executable, which can be found in the runtime binaries section here.

If you compiled with SDL, run with --window or -w to generate a window for output display.



Anything generally stable that represents more than incremental progress.


Alpha work in various states of disrepair. Might not compile, might be terribly broken.


I C the Light is licensed under the MIT/expat license, a copy of which is included in license.txt.

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