25
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. ...
- 561
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 ...
- 6,700
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 (...
- 304
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 ...
- 3,616
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 ...
- 2,312
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? ...
- 1,810
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 ...
- 246
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 ...
- 4,380
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. ...
- 8,397
11
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 ...
- 1,233
10
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 ...
- 24.8k
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 ...
- 6,700
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 ...
- 3,732
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 ...
- 7,751
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 ...
- 3,616
9
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) ...
- 24.8k
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 ...
- 546
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 ...
- 3,732
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 ...
- 24.8k
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 ...
- 434
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. ...
- 882
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 ...
- 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(...
- 3,616
7
votes
Accepted
Ambient Lighting
Correct is the OpenGL way. If you had a white light ( let's say vec3(255,255,255) )
and just simply added it to a blue object ( vec3(0,0,255) ), the object would seem to be white, which is wrong. But ...
- 353
7
votes
Accepted
Experimental real-time shadowing techniques?
There’s an interesting technique that’s been used in demoscene and Shadertoy projects for a while, and an analogue of which recently made it into Unreal Engine 4: using signed-distance fields and ...
- 2,132
7
votes
Accepted
Roughness Value of (Close to) Zero in Physically Based Rendering
Yes, I think it's expected that setting roughness = 0, combined with using point lights for illumination, leads to no visible specular highlight. The size of the highlight is infinitesimally small, so ...
- 24.8k
6
votes
Accepted
What are some new Real-Time Graphics Rendering Techniques to get closer to real life?
PBR isn't just a feature you "add to a rendering engine" but an entire philosophy how to approach solving rendering problems. This seems to be a common prevailing misconception when people talk about ...
- 3,616
6
votes
Accepted
Path tracer not rendering shadows
The problem appears to be unintentionally transparent surfaces
Although the image is grainy, it is sufficiently clear to estimate that all of the darker regions are due to surfaces facing away from ...
6
votes
What are Spherical Harmonics & Light Probes?
Spherical harmonics
Let's say you have some data in an array but you want to represent that data with a fewer number of bytes.
One way to do that could be to express the data as a function instead ...
- 7,751
6
votes
What's the concept of "Ray" really?
A ray is just a semi-infinite line, and casting the ray finds intersections between the ray and an object in the scene. It doesn't just tell you the position in space that the ray intersected the ...
- 6,700
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