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Comment by ginko | Hacker News Reader

Shadow mapping[1] has pretty much taken over at this point. This is mainly because of the high overdraw when rendering shadow volumes. You can also filter shadow maps to get soft shadows. This is not really possible with shadow volumes.

Raytraced shadows are starting to become feasible.

[1]http://en.wikipedia.org/wiki/Shadow_mapping

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Let's not forget that he was not the first to come up with this technique. From wikipedia [1]:

William Bilodeau and Michael Songy discovered this technique in October 1998, and presented the technique at Creativity, a Creative Labs developer's conference, in 1999.[2] Sim Dietrich presented this technique at both GDC in March 1999, and at Creativity in late 1999.[3][4] A few months later, William Bilodeau and Michael Songy filed a US patent application for the technique the same year, US 6384822 , entitled "Method for rendering shadows using a shadow volume and a stencil buffer" issued in 2002. John Carmack of id Software independently discovered the algorithm in 2000 during the development of Doom 3.[5] Since he advertised the technique to the larger public, it is often referred to as Carmack's Reverse.

[1] http://en.wikipedia.org/wiki/Shadow_volume

Ah, i initially heard about this as a fix for z-fighting.

<Sigh>, so many things are independently discovered.. Why do we still have patents??

Patents were originally on the specific mechanical system (like the Colt revolver) or chemical composition.

Math was excluded, as was computer code as a specific usage of mathematical logic.

But slowly patents on computer code made its way into patents, initially as code controlling mechanical or chemical processes.

According to an earlier comment, iD used this technique in Doom3. Would Carmack have had to pay patent license fees?

From my memory the only games which ended up using shadow volumes were Doom 3 and games based on the Doom 3 engine. Shadow maps always seemed like the way forward to me. That is purely based on my own "what looks better" scale. Given that most techniques in 3D programming are hacks to make things look better, I was surprised to see Carmack go down the shadow volumes path. It felt like he'd chosen it based on having nicer code versus an overall nicer looking game. This is all my opinion of course.

I find shadow volumes tend to look better, at least cleaner anyway. Shadow mapping if not properly done can look glitchy and aliased. One surprisingly bad offender was Skyrim.

I recall seeing both shadow mapping and volumes in Far Cry. Mapping was generally used outdoors in daylight (parallel casted light), and volumes for point lights. F.E.A.R. used volumes extensively also.

Are there actual production games using ray traced shadows? For non realtime rendering the advantages are soft shadows through lots of rays, rendering in one pass, and no geometry based artifacts. To do them in games though you have to trace against some sort of geometry and that geometry has to be sorted every frame. Simple proxy geo and dynamic bvhs are feasible I'm sure, but it seems to me to be a solution in search of a problem for the time being since all geo to be traced must stay in memory (and for transparency, the opacity textures as well). Now filtering cone sampling of volumes like the Unreal engine is a different story.

I’m wondering what is the technique behind the shadows in this recent Unreal demo: https://www.youtube.com/watch?v=4249b94KtyA

Looks like some sort of volumetric ray marching approach acceleratred by a signed distance field. Does anyone know what it is?

Not only overdraw but also having to be careful with how you craft the scene. SM pretty much allows for arbitrary scenes.

Also small nitpick: you don't filter the shadow map, but the resulting shadow response.

Cool, thanks a bunch for that info.

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