So, where are the stars?

In my pre­vi­ous rant about dynam­ic expo­sure in Elite Dan­ger­ous (which hon­est­ly applies to any oth­er space game made to date), I made a rough cal­cu­la­tion to pre­dict the bright­ness of stars as they should real­is­ti­cal­ly appear in pho­tos tak­en in out­er space. My pre­dic­tion was, that,

  • for an illu­mi­na­tion of sim­i­lar strength to that on earth,
  • if the sun­lit parts are prop­er­ly exposed,
  • and with an angu­lar res­o­lu­tion of about 2 arc min­utes per pix­el,

then the pix­el-val­ue of a promi­nent star should be in the order of 1 to 3 (out of 255, in 8-bit sRGB encod­ing). Since then I was curi­ous to find some real world val­i­da­tion for that fact, and it seems I have now found it.

ISS_and_Endeavour_EV+0

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Elite Dangerous: Impressions of Deep Space Rendering

I am a backer of the upcom­ing Elite Dan­ger­ous game and have par­tic­i­pat­ed in their pre­mi­um beta pro­gramme from the begin­ning, pos­i­tive­ly enjoy­ing what was there at the ear­ly time. ‘Pre­mi­um beta’ sounds like an oxy­moron, pay­ing a pre­mi­um for an unfin­ished game, but it is noth­ing more than pur­chas­ing the same backer sta­tus as that from the Kick­starter cam­paign.

I came into con­tact with the orig­i­nal Elite dur­ing christ­mas in 1985. Com­pared with the progress I made back then in just two days, my recent per­for­mance in ED is lousy; I think my com­bat rat­ing now would be ‘com­pe­tent’.

But this will not be a game­play review, instead I’m going to share thoughts that were inspired while play­ing ED, most­ly about graph­ics and shad­ing, things like dynam­ic range, sur­face mate­ri­als, phase curves, ‘real’ pho­tom­e­try, and so on; so … after I loaded the game and jumped through hyper­space for the first time (actu­al­ly the sec­ond time), I was greet­ed by this screen fill­ing disk of hot plas­ma:

ED001

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X-Plane announces Physically Based Rendering

I always won­dered when X-Plane would jump on the PBR band­wag­on. I like X-Plane, I think its the best active­ly-devel­oped (*) flight sim­u­la­tor out there, but I always felt that shad­ing could be bet­ter. For instance, there is this unre­al­is­tic ‘Lam­bert-shad­ed’ world ter­rain tex­ture, which becomes too dark at sun­set; anoth­er is the dread­ed ‘con­stant ambi­ent col­or’ that plagues the shad­ing of objects.

Now in this post on the X-Plane devel­op­er blog, Ben announces that Phys­i­cal­ly Based Ren­der­ing is a future devel­op­ment goal, yay! Then he goes on to say that, while sur­face shad­ing will be a solved prob­lem™ because of PBR, oth­ers like par­tic­i­pat­ing media (clouds, atmos­phere) would still need mag­ic tricks for the fore­see­able future. Con­tin­ue read­ing

Slides of my FMX 2013 presentation on Physically Based Shading

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.

Down­load “FMX 2013 Slides (Keynote for­mat)” fmx-11.zip – Down­loaded 2249 times – 8 MB


Down­load “FMX 2013 Slides (Pow­er­point for­mat)” fmx-111.zip – Down­loaded 3664 times – 8 MB

Velvet Assassin on Mac (Patch)

I just got news that Vel­vet Assas­sin has been port­ed over to the Mac and is avail­able on the App Store! 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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Cloud rendering and the relativity of whiteness

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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Comments on Advances in Real Time Rendering 2011

I final­ly got around to write some com­ments on this years Advances in Real Time Ren­der­ing held at SIGGRAPH 2011. Thanks to the RTR-team for mak­ing the notes avail­able. The talk about phys­i­cal­ly-based shad­ing in Call Of Duty has already been men­tioned in my pre­vi­ous post. So, in no par­tic­u­lar order:

Rendering in Cars 2
Christopher Hall, Robert Hall, David Edwards (AVALANCHE Software)

At one point, the talk about ren­der­ing in Cars 2 describes how they use pre-exposed col­ors as shad­er inputs to avoid pre­ci­sion issues when doing the expo­sure after the image has been ren­dered. I have employed pre-exposed col­ors with dynam­ic expo­sure in the past, and I found them tricky to use. Since there is a delay in the expo­sure feed­back (you must know the expo­sure of the pre­vi­ous frame to feed the col­ors for the next frame) you can even get expo­sure oscil­la­tion!

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The Blinn-Phong Normalization Zoo

It is good to see how phys­i­cal­ly based shad­ing is final­ly gain­ing momen­tum in real time graph­ics and games. This is some­thing I have been advo­cat­ing for a long time. Devel­op­ers are spread­ing the word. I was espe­cial­ly sur­prised to learn about Call of Duty: Black Ops join­ing the club [1]. Even a slick 60Hz-shoot­er with no cycles to spare can afford to do PBS today!

This leads me to the top­ic of this post, the nor­mal­iza­tion of the Blinn-Phong spec­u­lar high­light. Why am I writ­ing about it? It came to my mind recent­ly with the cur­rent batch of pub­li­ca­tions from peo­ple adopt­ing phys­i­cal­ly based shad­ing mod­els. This got me check­ing the maths again and I com­piled a list with nor­mal­iza­tion fac­tors for dif­fer­ent shad­ing mod­els, giv­en here in this post. I would also like to elab­o­rate a lit­tle on the mod­el that I wrote about in ShaderX7 [2]. Be aware this post is a large brain dump.

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