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axefrog

Member Since 08 Apr 2011
Offline Last Active Nov 22 2014 02:19 AM

Topics I've Started

Recommend a book on differential geometry

28 October 2014 - 12:56 PM

I'm currently partway through learning calculus and linear algebra for graphics programming (using books I bought on Amazon), but it's been brought to my attention that I really should add differential geometry to the list.

 

Can anyone recommend a good book on differential geometry before I try my luck with Amazon book roulette?


A radiometry question for those of you who own Real Time Rendering, 3rd Edition

26 October 2014 - 12:47 AM

I'm a bit confused by the following diagram (7.4) on page 207 of Real Time rendering, 3rd Edition:

 

2014-10-26_1634.png

 

The text before and after I think makes a few assumptions and doesn't quite explain what I'm looking at well enough. What I understand:

  • dw is the change in steradians/solid angle w
  • dA is the area irradiated by the light ray with respect to dw
  • n is obviously the surface normal
  • The orange line is clearly a light ray

Why am I confused? The light ray is apparently hitting a surface (hence the surface normal pointing away from the surface), and the angle depicted is the angle between the ray hitting the surface, and the surface normal. But what is the circle at dw indicating? My understanding was that the solid angle is easily visualised as a cone apexed at the light source, with the circle representing a patch surface on a sphere enclosing the light source. Why then is that circle in the diagram apparently situated at the light source? It seems to me that the cone in the diagram should be facing the other way.

 

p.s. I hope the authors don't mind me displaying this diagram. I will remove it and replace it with my own hand-drawn version if requested to do so.


With regards to texturing, what is "linear space" and "nonlinear space"?

24 October 2014 - 12:56 AM

On page 164 of Real Time Rendering (3rd Edition) there is the following passage:

 

"For textures encoded in a nonlinear space (such as most color textures), ignoring gamma correction when filtering will modify the perceived brightness of the mipmap levels. As you get further away from the object and the uncorrected mipmaps get used, the object can look darker overall, and contrast and details can also be affected. For this reason, it is important to convert such textures into linear space, perform all mipmap filtering in that space, and convert the final results back into nonlinear space for storage."

 

It's entirely possible that linear and nonlinear space were described at some earlier point, but I'm damned if I can find where. Please feel free to enlighten me...


Light theory - radiance vs material exitance?

22 October 2014 - 03:41 AM

I'm currently going through chapter 5 of Real Time Rendering and on page 110 (5.5. Shading) there is a distinction made between "exitance" of light from a material, or in other words, the counterpart of "irradiance" that is reflected from the material's surface, where irradiance is the measure of the amount of light hitting the surface, and "radiance", which is the brightness and colour of a single ray of light. It seems to me that the exitance value Mdiffuse, that equation 5.3 shows, represents a ray of light leaving the surface in a given direction is the same thing conceptually as the radiance value perceived at the receiving end of that ray of light. Why then does equation 5.4 then calculate the radiance Ldiffuse as a function of the exitance value? How are they not the same thing?


Steam OS survey - reflection of reality?

18 October 2014 - 09:17 PM

I was just looking at the Steam Hardware & Software Survey, and it shows 95.35% Windows usage, 3.42% Mac usage and 1.16% Linux usage. Naturally this is viewed through the filter of "people who use Steam". For those of you who see actual real sales of your games outside of Steam, do you observe similar distribution figures? Or is Steam more heavily used (proportionally) by Windows users, thus causing slanted numbers?

 

2014-10-19_1312.png


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