# Questions tagged [physically-based]

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### Roughness Value of (Close to) Zero in Physically Based Rendering

In my Direct Light Physically Based Renderer, when I set the roughness too low (ie. 0.0 or close) the specular reflection doesn't show, not even at high resolutions and at perfect angle with the ...
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### Image contribution function and reconstruction using filters

So I've been reading Physicall Based Rendering which in section 16.4.3 defines the "image contribution function" to be the following $$I_j = \int_\Omega h_j(X)L(X)d\Omega$$ where the variables are ...
106 views

### Tone Mapping in a physically based rendering ray tracer

I'm implementing a pbr ray tracer. Let's say that I'm at the end of the process: for each pixel pi, I accumulated the radiance value in vector pi = (radR, radG, radB). At this point, these values are ...
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### total internal reflection implementation in pbrt-v3

I've been implementing a path tracer, referring pbrt-v3. However, I'm a bit confused about its implementation. Code is here. It seems when we sample to do transmission, it tests if it meets a total ...
275 views

### PBR and Specular Aliasing

I have been following LearnOpenGL.com's tutorials on PBR. Everything makes sense and I wrote up a shader for my physically based renderer. I noticed that the results look great, however all of my ...
24 views

### Why need a $h$ parameter in the Geometry Function of a BRDF

Geometry Function in the specular BRDF term is defined as $G(l, v, h)$. Why need a $h$ since $h=\frac{l+v}2$. $f_{spec}(l,v) = \frac{F(h,v)G_2(l,v,h)D(h)}{4|n\cdot l||n\cdot v|}$ from "Real Time ...
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### kinematics and dynamics of a sphere in a spring mass system?

I am attempting to code a simple spring mass system simulation in which a sphere pendulus hangs from a string (a spring) by the top and then another sphere (controlled by the user) can move and ...
150 views

### How to set equivalent PDFs for cosine-weighted and uniform-sampled hemispheres?

I'm trying to add BRDFs to a very basic path tracer. Starting out, I'd like to convert just the Lambertian material, with two different sampling methods, to ensure that everything is working right. ...
181 views

### Physically Based Shading for Diffuse surfaces

So I am currently in the process of implementing Physically based Shading in my pathtracer using microfacet models and I'm quite stuck at comprehending light interaction with diffuse surfaces. First ...
102 views

### Rendering Equation for photons carrying flux

I am trying to understand the mathematical/physical foundations of photon mapping better. In the forward photon tracing step it is established, that the rays are carrying portions of total power (...
796 views

### For shader math, why should linear RGB keep the gamut of sRGB?

sRGB is often contrasted with "linear RGB." Images are stored on disk and passed to displays in sRGB, which is approximately perceptually uniform in intensity. Shader math is done in linear RGB, ...
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### Compute emitted importance of a pinhole camera

In section 16.1.1 of Physically Based Rendering the authors describe how we can check, if a given ray $r$ corresponds to one starting from the film area. They implement this check such that it works ...
362 views

### Ocean Wave Rendering

How could I generate the waves for a water body with whitecaps & foam and variable intensity of the waves? Is the surface a mesh with a normal map? Is there a formula for generating that? Is there ...
261 views

### PBR - How to handle multiple BSDFs and material type

So I am in the midst of writing my own path traced renderer and right now I have only implemented the old Blinn-Phong models where we separately calculated the diffuse and specular components of the ...
176 views

### How is Iridescence handled in a Path Tracer?

I have little knowledge of this topic but from what I gather in a Ray Tracer each ray is given its own wavelength as opposed to an RGB value. This automatically simulates Dispersion and Fluorescence. ...
214 views

### Interpreting Cornell Box data for path tracer

So I want to path trace a Cornel Box scene, but I don't understand the values given here in section 2 and 3. Cornell Box Data | Cornell University Program of Computer Graphics No.2 Lists surface ...
938 views

### Ray tracing: transforming ray to object's local space for intersection test

Im writting a raytracer, for which I want to be able to test intersections with implicit surfaces (in my case spheres). Without applying any transformation it works great, but I would like to upgrade ...
98 views

### How to validate whether a reflection model is implemented correctly?

I think this is one of the most important part when you write a physically-based renderer. The solution I came up with is to put a sphere to the scene with a constant background radiance. Solve the ...
4k views

### How physically-based is the diffuse and specular distinction?

The classical way of shading surfaces in real-time computer graphics is a combination of a (Lambertian) diffuse term and a specular term, most likely Phong or Blinn-Phong. Now with the trend going ...
173 views

### What is the physical interpretation of Normal, Roughness, Albedo and Metalness map?

In PBS context what is the metalness map? Are my interpretation of Normal, Roughness and Albedo map correct? I know almost for sure that: Normal map : Models the normals per differential region in ...
2k views

### Books to learn Ray Tracing [closed]

Recently I have developed and interest in Ray Tracing and like most computer graphics tutorials online there is nothing regarding implementation for a beginner like myself. So far I have only done ...
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### The reciprocity of BRDF

Many books describe that a BRDF has the following property (reciprocity): $$f_r(x, \Theta \to \Psi ) = f_r(x, \Psi \to \Theta)$$ Why is the above equation correct? I think the above equation ...
133 views

### What is the potential equation in PBR?

I'am studying PBR and the book introduce the potential equation. They said the potential equation can describe shooting algorithms better, and $W(x, \theta)$ describes the fraction of the radiance \$L(...
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### Mitsuba Bidirectional Framework

I'm confused by the Mitsuba bidirectional framework for quite a while now, especially by the different eval and connect ...
280 views

### Is there a material table for the Cook Torrance BRDF?

Is there a material table that lists all the specific values to obtain a certain type of material (e.g: copper or asphalt) available? I found this table in the paper: A Reflectance Model for ...
402 views

### How Sunlight is added in Bidirectional Path tracing?

How is distant directional light source(like sun) added in BDPT? If this is an indoor scene that gets sunlight through windows, how is this handled in BDPT(other than to consider Sun as a big disc far ...
759 views

### Better alternatives to the Lambert BRDF

After reading about the new Disney Diffuse BRDF, I have been wondering if this is currently the best Diffuse BRDF at the moment? How much more of a difference would this make compared to using a ...
108 views

### Trying to understand environmental cubemaps

I am trying to implement a physically based renderer, in OpenGL. I was planning to implement the Cook-Torrance BRDF. I read about radiance cubemaps (for reflections), like the one discussed here, for ...
391 views

### What is the most physically accurate model of surface materials possible in computer graphics?

I am looking for theoretical and implemented models to represent surface materials in software that strives for physical accuracy. Is BRDF really the best model? What alternatives are better? Why? ...
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### What are Spherical Harmonics & Light Probes?

What are Spherical Harmonics & Light Probes? How useful are they in computer graphics? What exactly do they do? I've heard the word spherical harmonics & Light Probes everywhere, from siggraph ...
2k views

### Depth of Field in Path Tracing: What do I do with the secondary ray?

How can I implement Depth of Field in my Path Tracer? I have read this article which explains the theory behind everything & I already have a good understanding of what this effect needs to ...
2k views

### Area Lights in Path Tracing

I have been following the scratchapixel ray tracing tutorials online which have been great at explaining the theory behind everything & how to implement it. However, I reached the point where I ...
127 views

### How is glint rendering done in Ray Tracing?

How is glint rendering done with ray tracing in the photo below? Is it just a simple normal map? I found a paper online that describes the exact same method used in the photo above but I have no ...
395 views

### Total emitted power of diffuse area light

I am reading the book Physically Based Rendering (Pharr, Humphreys). In the chapter on lights, they talk about approximating the total emitted power of different kinds of lights. For example, a point ...
306 views

### How are Physically Based Rendering Methods Researched?

Recently a question that came to my mind was that How are Physically Based Rendering Techniques researched and developed? Do people just use current equations by physicists or do they create their own?...
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### Alternatives to Ambient Occlusion

Recently I wanted to improve the lighting in my game engine, naturally I looked towards Ambient Occlusion. I was considering SSAO but are there any better techniques? Maybe some that are Physically ...
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### Material Layering

So after reading this Unreal Engine 4 Documentation page: https://docs.unrealengine.com/latest/INT/Engine/Rendering/Materials/LayeredMaterials/ (Which describes how to use material layering in UE4) ...
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### Better Shadow Mapping Techniques

Currently I have basic shadow mapping setup in my engine. I am currently trying to implement something more realistic like PCSS (percentage closer soft shadows), to get a more physically accurate ...