23 votes
Accepted

How is a light probe different than an environmental cube map?

There are two different common meanings of "light probe" that I'm aware of. Both of them represent the light around a single point in a scene, i.e. what you would see around you in all directions if ...
user avatar
  • 23.7k
23 votes
Accepted

Why are normal maps blue and purple in color?

Only tangent space normal maps are primarily blue. This is because the colour blue represents a normal of (0,0,1) which would be an unchanged normal when the triangle lies in the plane x and y, i.e. ...
user avatar
  • 541
17 votes

What are Spherical Harmonics & Light Probes?

Spherical harmonics If you know what a Fourier transform is, you already almost know what spherical harmonics are: they're just a Fourier transform but on a spherical instead of a linear basis. That ...
user avatar
  • 6,440
15 votes
Accepted

Efficient rendering with many light sources

Yes, but you need a paradigm shift. What you are accustomed is called forward rendering. You submit your geometry and then you proceed immediately with the shading pass. In the basic forward ...
user avatar
  • 2,468
15 votes

Rendering equation - why unsolvable directly?

I'm sadly not able to add a comment to the answer above (not enough reputation), so I will do it like this. I'd like to point out that what Dragonseel describes is simply an integral equation (...
user avatar
  • 304
14 votes
Accepted

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

The next step up from a pinhole camera model is a thin lens model, where we model the lens as being an infinitely thin disc. This is still an idealization that pretty far from modeling a real camera, ...
user avatar
  • 23.7k
14 votes

What is ambient lighting?

Traditional rendering solutions do not do account for secondary light bounces (called indirect light). Even with strategically placed fill lights you still have areas where none of the direct light ...
user avatar
  • 8,159
14 votes
Accepted

What are Spherical Harmonics & Light Probes?

Basics of Spherical Harmonics Spherical Harmonics is a way to represent a 2D function on a surface of a sphere. Instead of spatial domain (like cubemap), SH is defined in frequency domain with some ...
user avatar
  • 3,541
14 votes

Why are normal maps blue and purple in color?

Because a normal map is covering vectors from -1 to 1 it makes sense to stretch this range into 0->1 so all of it can be fit inside the range of RGB. So usually we apply a transform on the normal to ...
user avatar
  • 2,234
13 votes
Accepted

What is ambient lighting?

In this context, Ambient lighting refers to a very crude approximation of indirect lighting. Direct lighting from a direct source is relatively simple to evaluate ...
user avatar
13 votes

Rendering equation - why unsolvable directly?

The rendering equation is as follows: Now, the integral is over the sphere around the point $x$. You integrate over some attenuated light, incoming from every direction. But how much light comes in? ...
user avatar
  • 1,750
13 votes
Accepted

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

Talking about Linear RGB must be avoided because it does not tell you anything about the RGB colourspace intrinsics, i.e., Primaries, Whitepoint and Colour Component Transfer Functions. A few years ...
user avatar
12 votes

How to Calculate Surface Normals for Generated Geometry

I see mainly three ways of computing normals for a generated shape. Analytic normals In some cases you have enough information about the surface to generate the normals. For example, the normal of any ...
user avatar
11 votes
Accepted

How to Calculate Surface Normals for Generated Geometry

You simply dont want fully smooth results. While the commented method by Nathan Reed: "Calculate each vertex to face normal, sum them, normalize sum", generally works it sometimes fails spectacularly. ...
user avatar
  • 8,159
10 votes

How do shaped lights work?

In a path tracer, when tracing a ray to a light with a shape other than a point ("area light" is the usual terminology), you generally select a random point on the surface of the light. When enough ...
user avatar
10 votes
Accepted

Why is spherical harmonics used in low frequency graphics data instead of a spherical Fourier transform?

Spherical harmonics really are the "spherical Fourier transform" you're looking for. The kind of hack you mention in comments, of doing a 2D Fourier transform on a lat-long projection, suffers from ...
user avatar
  • 6,440
10 votes

Formula for the ambient light intensity of a scene?

Using an 'ambient light' term in your lighting calculations is an approximation of the indirect light reflected around the scene. Usually it's up to the artist to choose an appropriate value. There ...
user avatar
  • 3,502
10 votes
Accepted

Why Diffuse Light use max(N · H, 0) instead of just letting it be negative?

If lighting with multiple lights, they add together to make the final lighting value. A negative light would darken other lights, which is incorrect. This is also true if you add in specular ...
user avatar
  • 7,331
9 votes
Accepted

OpenGL specular shading - Gradient banding issues

This is a common problem with very subtle gradients. The problem is that the image is displayed with 8 bits per component and this is not quite enough precision to make a gradient that is smooth to ...
user avatar
  • 23.7k
9 votes
Accepted

Physically Based Area Lights

When I implemented real-time area lighting, there were two documents I kept referring to: "Moving Frostbite to PBR" by Sebastien Lagarde and "Real Shading in Unreal Engine 4" by ...
user avatar
  • 3,541
9 votes
Accepted

Modern way of light sources in OpenGL?

Why are they deprecated? Those functions are deprecated because the OpenGL API moved in favor of a programmable pipeline in contrast with the old fixed pipeline. The programmable pipeline allows the ...
user avatar
  • 516
9 votes
Accepted

What is a vertex normal used for?

First, I cannot imagine how could a vertex have a normal,... Welcome to the exciting field of computer graphics. The first thing that might lead to your confusion is to think about a vertex too much ...
user avatar
  • 1,115
8 votes
Accepted

Does PBR incur a performance penalty by design?

As mentioned in this answer, Physically-Based Rendering isn't a set number of things. It's a concept. It's akin to saying something is 'Environmentally Friendly'. There are many different techniques ...
user avatar
  • 3,502
8 votes
Accepted

Tweaking a glow shader to make it look better

Sigma and kernel size of Gaussian filter Regarding how to choose the sigma and the kernel size (pixels) of the Gaussian: you set the sigma based on how wide of a blur you want (judging it visually) ...
user avatar
  • 23.7k
7 votes
Accepted

What is "Object Space Lighting"?

According to the Star Swarm developers this helps them with LOD and enables greater shading scaling. Based on this I guess its simply texture space lighting. Because we do what we’re calling object ...
user avatar
7 votes
Accepted

Unlit objects in deferred rendering

Typically in a deferred engine, you would render unlit objects directly to the color buffer, bypassing the lighting system entirely. You would likely also output zeroes to the G-buffer so that ...
user avatar
  • 23.7k
7 votes
Accepted

Alternatives to Ambient Occlusion

Ambient occlusion cannot be physically based no matter what algorithm you use to calculate it. It's a simplification of global illumination that assumes all occluders only block light and are ...
user avatar
7 votes
Accepted

Bloom in DirectX

This effect is called light bloom. Its algorithm is usually a variation of the following: Render your scene (preferably in high dynamic range) to texture. Make a thresholding pass to another texture. ...
user avatar
7 votes
Accepted

Refraction in a Ray Tracer: What do with an intersection within the medium?

this is an interesting question (and I am actually an author on Scratchapixel so I can maybe help on that one)). Things go as follows: you cast the primary ray into the scene the ray hits the glass ...
user avatar
  • 656
7 votes
Accepted

Confused about prefiltering environment maps (Manson 16)

Your first quote is referring to "Split-sum approximation" presented in "Real Shading in Unreal Engine 4" by Brian Karis, and also referred in the paper [Kar13]: $$\frac{1}{N}\sum_{k=1}^N \frac{L_i(...
user avatar
  • 3,541

Only top scored, non community-wiki answers of a minimum length are eligible