You can do some pretty impressive things: https://shadertoy.com/

I skimmed it but didn't see any mention of "ray marching", which is raytracing done in a shader. GPUs are pretty fast now. You can just do that. However you do have to encode the scene geometry analytically in the shader - if you try to raytrace a big bag of triangles, it's still too slow. There's more info on this and other techniques at https://iquilezles.org/articles/

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kaoD 5 hours ago | parent | next [-]

Nitpick: "raymarching" is not "raytracing done in a shader" and it's not polygon-based.

Raymarching is a raytracing technique that takes advantage of Signed Distance Functions to have a minimum bound on the ray's distance to complex surfaces, letting you march rays by discrete amounts using this distance[0]. If the distance is still large after a set number of steps the ray is assumed to have escaped the scene.

This allows tracing complex geometry cheaply because, unlike in traditional raytracing, you don't have to calculate each ray's intersection with a large number of analytical shapes (SDFs are O(1), analytical raytracing is O(n)).

There are disadvantages to raymarching. In particular, many useful operations on SDFs only produce a bounded result, actually result in a pseudo-SDF that is not differentiable everywhere, might be non-Euclidean, etc. which might introduce artifacts on the rendering.

You can do analytical raytracing in fragment shaders[1].

[0] https://en.wikipedia.org/wiki/Ray_marching#Sphere_tracing Good visualization of raymarching steps

[1] https://www.shadertoy.com/view/WlXcRM Fragment shader using Monte Carlo raytracing (aka "path tracing")

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dahart 3 hours ago | parent [-]

> Raymarching is a raytracing technique…

Did you mean ‘raymarching is a technique…’? Otherwise you’re somewhat contradicting the first sentence, and also ray marching and ray tracing are two different techniques, which is what you’re trying to say, right?

Raymarching can be polygon based, if you want. It’s not usually on ShaderToy, but there’s no technical reason or rule against raymarching polygons. And use of Monte Carlo with ray tracing doesn’t necessarily imply path tracing, FWIW.

	▲	kaoD an hour ago \| parent [-]
		Sorry, let me clarify, the terms are used imprecisely. Some people use "raytracing" only for the ray intersection technique, but some people (me included, in the post above) consider it an umbrella term and raymarching, path tracing, etc. only as specific techniques of raytracing. So what I meant is "'raymarching' is not 'raytracing in shaders' but just a technique of raytracing, in shaders or not". I was not correcting OP, just adding clarifications on top. > Raymarching can be polygon based, if you want But not polygon-intersection-based, it'd still be a SDF (to an implicit polygon).

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spiralcoaster 2 hours ago | parent | prev | next [-]

Why were you expecting this article to specifically mention ray marching? It looks like a comprehensive beginner article on what shaders are, not an exhaustive list of what you can do with them.

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ianthehenry 4 hours ago | parent | prev [-]

The next chapter is about SDFs, but it is not available yet.

https://www.makingsoftware.com/chapters/rays-and-sdfs