Yes, sRGB is like µ-law encoding

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I vaguely remem­ber some­one mak­ing a com­ment in a dis­cus­sion about sRGB, that ran along the lines of

So then, is sRGB like µ-law encoding?

This com­ment was not about the color space itself but about the spe­cific pixel for­mats nowa­days branded as ‘sRGB’. In this case, the answer should be yes. And while the tech­ni­cal details are not exactly the same, that anal­ogy with the µ-law very much nails it.

When you think of sRGB pixel for­mats as noth­ing but a spe­cial encod­ing, it becomes clear that using such a for­mat does not make you auto­mat­i­cally “very picky of color repro­duc­tion”. This assump­tion was used by hard­ware ven­dors to ratio­nal­ize the deci­sion to limit the sup­port of sRGB pixel for­mats to 8-​bit pre­ci­sion, because peo­ple “would never want” to have sRGB sup­port for any­thing less. Not true!Screen Shot 2014-03-06 at 19.02.54I’m going to make a case for this later. But first things first.

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Spellforce 2 Demons of the Past

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Spell­force 2 was released in 2006 and will be 8 years old by april. Nev­er­the­less, the third add-​on of the series shipped a month ago. Talk about a long seller!

Of course I’m attached to SF2 because I wrote many parts of its engine back then. This time I was briefly involved to help the devel­op­ers include my attribute-​less nor­mal map algorithm. The orig­i­nal SF2 did not have any nor­mal maps, and there­fore none of the orig­i­nal art assets comes with tan­gent space infor­ma­tion. This is an ideal sce­nario to pimp up the visu­als with­out touch­ing the geom­e­try, sim­ply by mak­ing a shader change and adding nor­mal maps. Con­tinue read­ing →

Slides of my FMX 2013 presentation on Physically Based Shading

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I was kindly invited by Wolf­gang from Con­fetti FX to speak at the FMX 2013 con­fer­ence about phys­i­cally based shad­ing (within the scope of the Real Time Ren­der­ing day). Since I remem­bered the FMX as a con­fer­ence for visual arts, I made the pre­sen­ta­tion inten­tion­ally non-​technical, for fear of alien­at­ing the lis­ten­ers. In ret­ro­spect, my guess was a bit too con­ser­v­a­tive, as there were quite a num­ber of pro­gram­mers in the audience.

Screen Shot 2013-04-24 at 14.53.58

Nev­er­the­less, here are the slides for down­load (with all notes included). The Keynote for­mat is the orig­i­nal and the Pow­er­point for­mat was exported from that and is a lit­tle bro­ken, so you should use the Keynote ver­sion if you can read it.

FMX2013 (Keynote for­mat) (1272)
FMX2013 (Pow­er­point for­mat) (2018)

Followup: Normal Mapping Without Precomputed Tangents

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This post is a follow-​up to my 2006 ShaderX5 arti­cle [4] about nor­mal map­ping with­out a pre-​computed tan­gent basis. In the time since then I have refined this tech­nique with lessons learned in real life. For those unfa­mil­iar with the topic, the moti­va­tion was to con­struct the tan­gent frame on the fly in the pixel shader, which iron­i­cally is the exact oppo­site of the moti­va­tion from [2]:

Since it is not 1997 any­more, doing the tan­gent space on-​the-​fly has some poten­tial ben­e­fits, such as reduced com­plex­ity of asset tools, per-​vertex band­width and stor­age, attribute inter­po­la­tors, trans­form work for skinned meshes and last but not least, the pos­si­bil­ity to apply nor­mal maps to any pro­ce­du­rally gen­er­ated tex­ture coor­di­nates or non-​linear defor­ma­tions. Con­tinue read­ing →

Velvet Assassin on Mac (Patch)

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I just got news that Vel­vet Assas­sin has been ported over to the Mac and is avail­able on the App Store! (It is that game for which I wrote about half of the engine code and the shad­ing model.) How­ever, I was not at all involved in the Mac port and I don’t know the devel­op­ers who did — it came as a sur­prise to me as to any­one else in the for­mer team. Here is a direct iTunes link: http://itunes.apple.com/app/id586878367.

Shader Bug on ATI graphic cards

Unfor­tu­nately there is a shader bug with ATI graph­ics chips. It hap­pened to me while try­ing it out on a 2011 iMac with an ATI Radeon HD 5670. I got reports from friends that this is not a prob­lem of the Mac port itself but it hap­pens on PC too. The prob­lem is related to ATI chips with dri­vers that are newer than 2010 or so. Here is a screenshot:

Screen shot 2013-01-11 at 04.09.06

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FlipCode is back

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Kurt has taken steps to revive Flip­Code.

Flip­code was a place to dis­cuss gamedev + algo­rithms with a unique flair and an out­stand­ing audi­ence, some­thing IMHO gamedev.net never matched. I, too, was a reg­u­lar vis­i­tor, poster, and also con­tributed the odd arti­cle and an IOTD. Ter­rain engines bor­der­ing on 100k polys with­out HW T&L will be for­ever in the past, but the spirit will live on.

Branchless Matrix to Quaternion Conversion

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A rou­tine to con­vert a matrix to a quater­nion was given by Ken Shoe­make [1], and seems to have been accepted as a ‘fact of life’. The code is orga­nized around a switch of four branches, depend­ing on the sign of the diag­o­nal matrix ele­ments. Is it pos­si­ble to do the con­ver­sion entirely with­out branches? No, not in gen­eral, if you must pro­tect against any and all sin­gu­lar­i­ties. Is it pos­si­ble, then, to expand the singularity-​free domain of a branch­less ver­sion so it cov­ers a use­ful range? Well yes, that’s what this post is about. Con­tinue read­ing →

OpenGL 4.3

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I just got the news about the OpenGL 4.3 spec, which was released today, and is avail­able at http://www.opengl.org/registry/. The spec doc­u­ment has been reor­ga­nized and cleared up con­sid­er­ably and is a lot eas­ier to fol­low than the pre­vi­ous spec­i­fi­ca­tions. New fea­tures include (ordered by impor­tance for my projects):

  • Queries for inter­nal tex­ture for­mat parameters
  • Debug out­put callbacks
  • Com­pute shaders
  • Tex­ture views
  • and oth­ers

I’m cur­rently on a project where com­pat­i­bil­ity and scaleabil­ity is prime, so the first two fea­tures are very wel­come as devel­op­ment aids to make the code run robustly on a vari­ety of plat­forms. Com­pute shaders and tex­ture views are of course cool, but require the newest hard­ware, so they are lower in my list.

A nice touch by Nvidia to make to expose the new func­tion­al­ity as exten­sions on older hard­ware.

Cloud rendering and the relativity of whiteness

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Here are some philo­soph­i­cal and rendering-​related ques­tions that I took home from the last vacation. What’s the color of clouds? The stan­dard answer would be, white.
What’s the color of snow? Again, white. Ok, then look at the fol­low­ing pic­ture, where the snow seems con­sid­er­ably whiter. This is the case in almost all pho­tos that I took.

There is an image on Wikipedia from the same gen­eral area on which the bright­ness dif­fer­ence between clouds vs snow is even more pronounced. If you look at the directly lit parts of the snow and con­sider it white (#ffffff), then the directly lit parts of the clouds are at most 50% grey (#bbbbbb). Is that an evi­dence of air pol­lu­tion? Unlikely! (At least not in Tyrol).

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