• Announcements

    • khawk

      Download the Game Design and Indie Game Marketing Freebook   07/19/17

      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
Sign in to follow this  
Followers 0
Chris_F

Shading metals

4 posts in this topic

What's the best way to go about geting realistic metals? I haven't seen it mentioned much. Currenly I am calculating my frenel term as a float3 with schlick's approximation, and different zero incident values based on the reflectance values you can get from here: (http://refractiveindex.info/)

 

Is this a close enough approximation? Are there better ways of handeling it? The colors seem about right to me, and the specular highlight turns white at glancing angles which seems right.

2

Share this post


Link to post
Share on other sites

Depends on how much work you want to go into, and your target platforms.

 

Good enough can be, well, good enough. As long as it's handled is all specular/no diffuse, it can look fine. But if you really wanted to get something better you could apply a better BRDF that handles reproducing metallic materials better, take a look at his stuff:

 

http://www.cs.cornell.edu/~srm/publications/EGSR07-btdf.pdf

http://renderwonk.com/publications/s2010-shading-course/gotanda/course_note_practical_implementation_at_triace.pdf

0

Share this post


Link to post
Share on other sites

Oh wait, you want to do metals with the fresnel equations? If that's the case, your formula from the other thread won't work. Metals usually have complex reflective indices (complex numbers). Fresnel's equations work with complex numbers though, your implementation just doesn't. You need complex multiplication, complex addition and the absolute value (which you didn't implement) needs to work with complex numbers as well. Also since metals have chromatic reflections you would have to calculate your fresnel term for all 3 color channels. I'd use Schlick's approximation, reduce most of it to constant time, and reduce other parts of the formula to scalar calculations, while only the necessary parts get calculated for all color channels.

 

Here's approximately how that code should look like. You should probably calculate the constant part per vertex or per draw call on the CPU, if possible:

 

float2 f0CmplxRed = cmplxDiv(cmplxSub(n1Red, n2Red), cmplxAdd(n1Red, n2Red));
float2 f0CmplxGreen = cmplxDiv(cmplxSub(n1Green, n2Green), cmplxAdd(n1Green, n2Green));
float2 f0CmplxBlue = cmplxDiv(cmplxSub(n1Blue, n2Blue), cmplxAdd(n1Blue, n2Blue));

float3 f0Sqrt = 0;
f0Sqrt.r = cmplxAbs(f0CmplxRed);
f0Sqrt.g = cmplxAbs(f0CmplxGreen);
f0Sqrt.b = cmplxAbs(f0CmplxBlue);

float3 f0 = f0Sqrt * f0Sqrt;
float3 cf0 = 1 - f0;

foreach (light)
{
	float factor = pow(1 - dot(L, H), 5);
	float3 fresnel = f0 + cf0 * factor;
} 

 

 

1

Share this post


Link to post
Share on other sites

Oh wait, you want to do metals with the fresnel equations? If that's the case, your formula from the other thread won't work. Metals usually have complex reflective indices (complex numbers). Fresnel's equations work with complex numbers though, your implementation just doesn't. You need complex multiplication, complex addition and the absolute value (which you didn't implement) needs to work with complex numbers as well. Also since metals have chromatic reflections you would have to calculate your fresnel term for all 3 color channels. I'd use Schlick's approximation, reduce most of it to constant time, and reduce other parts of the formula to scalar calculations, while only the necessary parts get calculated for all color channels.

 

Here's approximately how that code should look like. You should probably calculate the constant part per vertex or per draw call on the CPU, if possible:

 

float2 f0CmplxRed = cmplxDiv(cmplxSub(n1Red, n2Red), cmplxAdd(n1Red, n2Red));
float2 f0CmplxGreen = cmplxDiv(cmplxSub(n1Green, n2Green), cmplxAdd(n1Green, n2Green));
float2 f0CmplxBlue = cmplxDiv(cmplxSub(n1Blue, n2Blue), cmplxAdd(n1Blue, n2Blue));

float3 f0Sqrt = 0;
f0Sqrt.r = cmplxAbs(f0CmplxRed);
f0Sqrt.g = cmplxAbs(f0CmplxGreen);
f0Sqrt.b = cmplxAbs(f0CmplxBlue);

float3 f0 = f0Sqrt * f0Sqrt;
float3 cf0 = 1 - f0;

foreach (light)
{
	float factor = pow(1 - dot(L, H), 5);
	float3 fresnel = f0 + cf0 * factor;
} 

 

But the complex number math is only nesisarry to get the zero incident reflection value from the complex IOR. The website I linked not only lists the complex IORs, but also the reflectance values for arbitrary wavelengths at arbitrary incidents, so I can simply input the f0 values into the shader as a constant for my material or from a texture map. No need to work in term of IOR. I just wanted to know if calculating the reflectance coeficient for just R, G and B was a close enough aproximation to get realistic metal specular reflections.

0

Share this post


Link to post
Share on other sites

he website I linked not only lists the complex IORs, but also the reflectance values for arbitrary wavelengths at arbitrary incidents

I know this website, I've used it quite some time before :)

 

so I can simply input the f0 values into the shader as a constant for my material or from a texture map. No need to work in term of IOR.

I just wanted to let you know, that you need to work with all the 3 channels and the complex numbers. Like I said, you could do it per pixel, per vertex or per draw call on the CPU and simply input f0 and maybe also cf0 into the shader as constants. It depends on where you get your values. If n2Red, n2Green, n2Blue would be stored in a texture, you would have to do it per pixel, or you bake your f0 values into a texture and use the baked texture instead. But if you can do it per draw call, go ahead and calculate it on the cpu.

 

I just wanted to know if calculating the reflectance coeficient for just R, G and B was a close enough aproximation to get realistic metal specular reflections.

Yes, that should be enough. You should worry more about the microfacets though. Blinn-Phong is not such a good distribution term for metals and even more important is shadowing and masking of the microfacets: the geometry / visibility term.

0

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0