Questions tagged [physics]

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35 votes
2 answers
6k 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 ...
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15 votes
2 answers
896 views

Fresnel reflectance of gold: red channel greater than 1?

I've been trying to understand some of the physical principles behind light and material interaction lately. In his talk Physics and Math of Shading, Naty Hoffman explains Fresnel reflectance and ...
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  • 2,223
14 votes
2 answers
2k views

How to build a decent lens/camera objective model for path tracing?

I have written a small path-tracer after learning and experimenting on smallpt. The only thing that I did not write (and understood) myself is how the initial rays are computed and fired from the ...
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13 votes
3 answers
1k views

What explains the high specularity of metals?

From my understanding, the specular color usually refers to the amount of light that is reflected when the surface is lit at normal incidence, and is noted $F_0$ or $R_0$. Moreover, for non metal ...
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13 votes
4 answers
496 views

What physical properties are “lacking” to keep this 3D scene from looking like a real photograph?

So I know that I'm basically asking to identify the main problem to be solved in creating realistic 3d Graphics, but as someone without much technical experience in the field, I'm curious that if ...
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  • 865
10 votes
2 answers
730 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 ...
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9 votes
1 answer
249 views

How could I check the correctness of my result of fluid simulation?

I wrote a particle based fluid simulating program. It's hard to tell if I get the right result. The visualized result seems reasonable, but some part of it looks weird. I don't know wether it's a ...
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  • 193
8 votes
5 answers
717 views

Why does the 1/r² term appear with point sources?

I'm currently reading some books on radiometry. They mention that radiance is constant along a ray. It doesn't change with distance. However, I've seen some raytracer and they put the 1/r² factor when ...
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  • 149
7 votes
1 answer
1k views

Resulting Probabilty Density in Path Tracer for paths using Next Event Estimation

I am trying to implement my own Gradient Domain Path Tracer by following the code of this guy who already implemented it: https://gist.github.com/BachiLi/4f5c6e5a4fef5773dab1 I already managed to ...
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  • 325
7 votes
2 answers
142 views

Overlaying graphics on particle simulation

How can I overlay graphics on particle simulations? For instance if I am representing a liquid or gas with tons of little points how can I make those points look like a liquid or gas? Take Nvidia Flex ...
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6 votes
1 answer
3k views

What's the difference between irradiance and fluence/radiant exposure?

A paper$^1$ I'm reading says fluence measures the incoming radiance from all directions and that fluence is similar to irradiance. It's defined by $\phi(x) = \int_{4 \pi} L(x, \vec{\omega'}) d\omega' $...
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  • 225
5 votes
2 answers
172 views

Rendering Hypercentric Perspective

I came across some Non-Euclidean Games which involve Hyperbolic Spaces, Spherical Spaces, Portals, etc. And, I noticed that they give quite deep feel of what Non-Euclidean Spaces feel like. So, I was ...
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5 votes
1 answer
988 views

Can we use PhysX in WebGL?

I'm new to GL stuff (coming in via WebGL, with no direct OpenGL experience). Can we use PhysX with WebGL?
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  • 255
4 votes
2 answers
600 views

What is the effect of the BRDF denominator?

I was reading a paper on BRDF. I've come across this formula : $$ f(\omega_i, \omega_o ) = \frac{FDG}{4(N.V)(N.L)}$$ The (N.L) term can be cancelled by the cosine term which appears in the rendering ...
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  • 149
4 votes
2 answers
356 views

2D metaballs with marching squares and linear interpolation

I struggle do understand how linear interpolation works in the marching square rendering algorithm context. I created simple example in GDScript (Godot) of random floating metaballs to demonstrate ...
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  • 141
4 votes
1 answer
281 views

Creating Sparks using Code

I'm new to this area and have less knowledge. I want to create some graphics like sparks and lightning by writing some code, using my own physics. I don't want to use some engine, However I can use ...
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  • 41
3 votes
0 answers
85 views

What is a good algorithm, and framework, to calculate centres of gravity or mass (cog)?

I'd like to take an photograph, subdivide it into a tesselation, either of squares, or (ideally), hexagons, and then find the centre of gravity (or, if you prefer, centre of mass) of each cell of the ...
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2 votes
2 answers
185 views

Understanding lighting for physically based rendering

i wanted to ask if you know the best books or resources to understand light physics. I have heard that Subrahmanyan Chandrasekhar's book "Radiance Transfer" is very good. Any other books or ...
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2 votes
2 answers
119 views

Why is the approximation valid, in the formula provided by Brian Karis?

I'm sorry I'm bringing this topic up again, but I need to expound some of the topics. With reference to this question, I was wondering if someone can help me out in expanding some of the details. In ...
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2 votes
2 answers
124 views

Blackbody curve to floating RGB

I want to set the color of the lamps in my game with a black body curve, but the approximations I can find for it are all in sRGB color space; and I want it in linear floating RGB. The closest thing ...
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2 votes
2 answers
254 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 ...
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2 votes
1 answer
208 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 (...
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  • 121
2 votes
0 answers
76 views

Implementing monte carlo path traced refractions problem

I am writing a forward monte carlo path tracer with the added feature of specular refractions for transparent materials, I have managed to come this far but something is not quite right and I am ...
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  • 21
1 vote
1 answer
61 views

How would I create a virtual cabling system?

I am trying to devise a GUI system that functions as a virtual patchbay, as seen in something like Logic Studio's environment editor, or seen in virtual synthesizers that use virtual patchcables. I'm ...
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  • 13
1 vote
1 answer
125 views

Prove radiance contributions of deeper paths fade away

When ray tracing, I find it intuitively clear that deeper paths have a lower contribution to the overal picture than shorter paths. This is the main reason why it is generally okay to render a picture ...
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  • 111
1 vote
1 answer
109 views

Why are BRDF and the lighting uncorrelated?

In relation to this question, in the accepted answer I have a trivial question probably. W.r.t. the following integral $$ L_o(x\rightarrow \Theta) = \int_{\Omega_x} f_r(x,\Psi\rightarrow\Theta)L_i(x\...
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1 vote
1 answer
71 views

Spring damping in Energy Function

Supposing a behavior function $C(x_1, \ldots, x_n)$, then we have a scalar potential energy function $E = \frac{k_s}{2}C\cdot C$ where $k_S$ is stiffness constant. Hence, the force is as follows $...
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  • 523
1 vote
1 answer
1k views

Hooke's Law vector form

I'm studying spring model. There is a suggested equation (Hooke's Law vector form) But, I couldn't understand how to derive that equation. I'm reading 'Computer Animation Algorithms and Techniques ...
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  • 523
1 vote
1 answer
390 views

Beginner CG Research Project [closed]

This summer I will be working with a professor on a research topic of my choice, in the field of graphics & simulation. While my professor is knowledgeable in the area he is being very hands off ...
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  • 13
0 votes
1 answer
45 views

How to ensure that a randomly-generated velocity vector moves the camera forward within a valid arc?

I spawn a camera in a scene using random coordinates for x and y and setting z=0 and orient ...
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  • 241
0 votes
1 answer
67 views

Fastest Simulation Of Mass Spring Systems

I'd like to simulate a 4-dimensional cloth in the web browser, since browsers don't offer great ressources for numerical computation, I'd like to know which algorithm uses the least amount of ...
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  • 125
0 votes
1 answer
100 views

How to rotate a shape in another 3D software so that the rotation matches with the rotation in Blender?

I import a mesh in Blender, export it with setting axis_forward='-Z', axis_up='Y', import in NVIDIA's FleX, rotate it and store it on disk; I call this mesh ...
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  • 241
0 votes
0 answers
75 views

OpenGL Compute Shader Vector Subtraction Not Working As Expected

all. I am currently working on a compute shader in GLSL intended to simulate visualizations of general relativity by ray tracing in the Schwarzchild spacetime geometry. I'm about halfway through ...
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0 votes
0 answers
47 views

3D Bouncing Cube

I'm trying to write a little program with a bouncing cube but I can't find the right x, y, z and angle for it. I have these lines: ...
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