• 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
lipsryme

Need help with microfacet brdf

5 posts in this topic

I'm trying to implement a microfacet brdf but my results are wrong somehow.
That's why I was hoping someone can point out what I'm doing wrong or what I'm missing.

-> see below Edited by lipsryme
0

Share this post


Link to post
Share on other sites
Hi

I see at least your half vector is wrong.

"float3 H = normalize(-L - V);" should be: float3 H = normalize(-L + V);
0

Share this post


Link to post
Share on other sites
Actually doing it like that makes it not work at all.
My View direction is being calculated like this:
[CODE]
// Calculate Position from linear view space depth
float3 ViewRay = input.PositionVS.xyz;
float depth = DepthTarget.Sample(PointSampler, input.UV).r;
float3 ViewDir = ViewRay * depth; // subtraction by the cam position not needed since we're already in view space
[/CODE]

Have to say I got it working now with a phong distribution but anything else (the commented out part) gives me wrong results.
[CODE]
// Compute Fresnel Term (F) using Schlick's approximation
float LdotH = max(0, dot(-L, H));
float base = 1 - LdotH;
float exponent = pow(base, 5.0f);
float3 F = saturate(SpecularAlbedo + (1 - SpecularAlbedo) * exponent);

// Lambert
float3 kd = NdotL;
Lr.rgb += (kd / PI) * Ei;


// Normalized Blinn-Phong distribution (D)
float D = 0.0f;
float NdotH = max(0, dot(N, H));
D = ((SpecularPower + 2) / 2 * PI) * pow(NdotH, SpecularPower);

// Beckmann distribution (D)
//float NdotH = max(0, dot(N, H));
//float NdotH2 = NdotH * NdotH;
//float NdotH4 = NdotH * NdotH * NdotH * NdotH;
//float SpecularPower2 = SpecularPower * SpecularPower;
//float Beckmann_exponent = -((1 - NdotH2) / (SpecularPower2 * NdotH2));
//float D = 1 * exp(Beckmann_exponent) / PI * SpecularPower2 * NdotH4;

// Trowbridge-Reitz (GGX) distribution
//float NdotH = max(0, dot(N, H));
//float SpecPow2 = SpecularPower * SpecularPower;
//float D = SpecPow2 / PI * pow(((NdotH*NdotH) * (SpecPow2 - 1) + 1), 2);

// Cook-Torrance approximation (G)
float NdotV = max(0, dot(N, V));
float G = 1.0f;

float3 nominator = F * G * D;
float denominator = 4 * ((LdotH+0.000001f) * (LdotH+0.000001f));
Ls.rgb += nominator / denominator;
[/CODE]

Beckmann or Trowbridge-Reitz doesn't... Edited by lipsryme
0

Share this post


Link to post
Share on other sites
Pretty sure the Beckmann distribution is actually this (and same comment for GGX, I would guess):

[CODE]float D = 1 * exp(Beckmann_exponent) / (PI * SpecularPower2 * NdotH4);[/CODE]

This is my path tracer code for Beckmann, it uses a raw BRDF so you'll have to modify the inputs (the incident vector goes towards the surface, the exitant vector goes away from it). The vector * vector operation is the dot product. Also I'm not using the tangent formula trick yet whereas you seem to be.. sorry:

[url="http://pastebin.com/pHqCH1dc"]http://pastebin.com/pHqCH1dc[/url]

Might have gone overboard with the absolute values but I was dealing with refraction at the same time and didn't want to take risks [img]http://public.gamedev.net//public/style_emoticons/default/smile.png[/img]

EDIT: dammit, why are the code tags munching my newlines?
EDIT: pastebin it is! Edited by Bacterius
0

Share this post


Link to post
Share on other sites
Your GGX distribution is missing a parenthesis. Everything should be in the denominator except the alpha^2. So the correct implementation would be:

[font=courier new,courier,monospace]float NdotH = max(0, dot(N, H));
float SpecPow2 = SpecularPower * SpecularPower;
float D = SpecPow2 / (PI * pow(((NdotH*NdotH) * (SpecPow2 - 1) + 1), 2));[/font]

[quote name='Bacterius' timestamp='1351996036' post='4997064']
float G = min(1, min(2 * NdH * NdV / VdH, 2 * NdH * NdL / VdH));
[/quote]

Don't do it this way, you are wasting instructions this way. Do it like that:
[font=courier new,courier,monospace]float G = min(1, 2 * NdH / VdH * min(NdV, NdL));[/font]
0

Share this post


Link to post
Share on other sites
I'm still getting crazy high values (basically the entire mesh white). Does the input alpha have to be ridiculously high ?
edit: hmm no higher values don't seem to fix this.
edit2: ok so when only outputting D or D*F it looks more like it should (still very bright). Is there something wrong with my Geometry term ? Edited by lipsryme
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