GoKawiilBlogpost Surfel-based global illumination on the web Can we use WebGPU to compute real-time global illumination with surface patches called surfels? Does it look good enough? Is it fast enough? And can we finally construct viable compute-heavy rendering pipelines right here on the open web? Join me on this journey and let's find out!
Above is a quick illustration of what we'll be exploring step by step, through a series of interactive visualizations. But before we continue down that path, dear reader, I implore you to make a choice.
A brief history of light
Greetings, fellow adventurer! Let's begin.
Of course at first, there was nothing, not even light. Then very shortly after the big boom, maybe a second after, the first particles of light were created. Unfortunately for them, for a long, long time the universe was so full of energy, so hot and dense, that these photons could not travel where they wanted to go, but instead almost immediately ran into electrons and scattered, kind of like trying to shine a flashlight through the thickest fog you've ever seen.
Then after some time things cooled down just a bit, it was still scorching hot, but cold enough that electrons and protons stopped frolicking out in the open, became friends and moved in together into atoms. The poor photons that were constantly crashing into things suddenly had space to move - and the fog lifted. The light that was released then is the oldest light we can observe, the cosmic microwave background.
Alas, after this brief spectacle of light, the universe was plunged into darkness yet again. With the photons from the initial boom gone with the wind, there was nothing anywhere that could make new ones. And so the universe waited. Global illumination from year 380,000 to year 400 million was easy peasy, finalColor = vec4(0,0,0,0).
Finally, roughly half a billion years after the universe was born, a bunch of hydrogen bits clumped together so hard that they self-ignited, fused into helium atoms, during which super high energy photons were created, and a new type of lightbulb came into existence - a star. Now, the behaviour of these photons isn't something people would write global illumination theses about - in fact, if Earth was “illuminated” by them there would be no people at all, it would be a sterile frozen wasteland. No, these energetic youngsters need to first calm down and bounce around the star's interior for 100,000 years or so, before all the particle interactions in this cosmic kindergarten whittle them down to visible light energy levels and they reach the surface of the star. Now adults, they are free to roam the universe at the speed of light.
It is precisely these photons that we'll be trying to wrangle in this post. The subject of fascination for many scientists (Haytham's Book of Optics, Newton's corpuscles, Young's light waves, Planck's quanta, Einstein's photoelectric effect) and artists (Leonardo's study of light scattering, Monet's series studying the color of stone in different light, Turner's light studies, Vermeer's alleged mechanical aids) alike, these messengers of light behave in many interesting ways (scattering, diffraction, refraction, gravitational lensing, just to name a few), but for the purposes of our exploration, we're particularly interested in diffuse reflection. Or as Leonardo put it in the late 15th century, the effect of light by which:
It happens very rarely that reflections are of the same color as the body [from which they come] or of the object where they meet. For example: Let the spherical body d f g e be yellow, and the object reflecting its color upon it be b c, which is blue. I say that the part of the spherical body that is struck by this reflection will be tinged a green color, provided that b c is illuminated by the air or the sun.
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