very simple pure CPU raymarching demo

[ketmar via Digitalmars-d-announce]

the following[1] is the demo of pure CPU implementation of the 
famous "raymarching" algorithm[2]. of course, doing that in GLSL 
shader will be many times faster (10x? 20x? dunno), but i'm too 
lazy to port the necessary gl headers (and don't want to use 
derelict for some random reason ;-), so i did it on CPU.

it's basically the fragment shader code, executing on CPU instead 
of GPU.

of course, one can use more threads to render image parts, but 
i'm too lazy to implement that (let's say that i left this as an 
excercise for a reader; i know you all love such "excercises").

you will need Adam's simpledisplay.d and color.d from here[3].

no OpenGL required.


[1] http://ketmar.no-ip.org/dmd/zrm3_adam_trd.d
[2] 
http://iquilezles.org/www/articles/raymarchingdf/raymarchingdf.htm
[3] https://github.com/adamdruppe/arsd