Practica Boxel

Sat 30 January 2021
By Bram

Today, I unveiled my latest work-in-progress: "Practica Boxel." Here is the video, introducing the tool, which does WYSIWYG Global Illumination.

In a way, it is a continuation of my SIMD-raytracer of a few years back. But when doing that (on CPU with AVX) I realised that only firing one primary ray for a pixel, and only one shadow-ray, with optionally a specular bounce, will get you limited advantages over rasterizing triangles. Shadows are easier, with no need of kludges like shadowmaps. But that's about it.

The real big win when leaving the rasterizing world, is when you compute indirect light, with diffuse bounces. You can get that awesome soft look from radiosity solutions, e.g. But calculating indirect diffuse is prohibitively expensive for a CPU. For that, you need the power of thousands of GPU cores.

So I wrote CUDA code to do this, leveraging the algorithm by Henrik Wann Jensen: Photon Mapping. A straight up path tracer is too slow for 60FPS use, but a Photon Mapper can be made fast enough, when your scene is simple enough.

So how do we get a simple scene? Use boxes! And thus, Practica Boxel was born. The name is a pun on Magica Voxel, but instead of using voxels, abitrary sized boxes (still axis aligned) are used.

Since no proper box-editing tool seems to exist, I had to write my own. This task is made a little easier when you have Dear ImGui do the heavy lifting w.r.t. user-interface.

So, what does accurate lighting bring to games? Well, for starters, you can prominently feature Darkness in your games. No ambient light, No black screens, but actual darkness, as can be witnessed in this 2 second clip:

"And then, the tomb closed..."
(Proper GI is an excellent basis for a convincing horror game.)

—Bram Stolk (@BramStolk) January 24, 2021

Where will this project go next? I could turn it into an indie game, but my preference would be to get external funding to create a complete tool-suite around the technology and let others make the games with it.