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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. perpendicular to the surface. The tangent, x and bi-tangent, y (also referred to as bi-normal) are encoded in the red and green channels and these form to create ...
22
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 you were shrunk down to a tiny size and stood at that point.
One meaning is a spherical harmonic representation of the light around a point. Spherical ...
17
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 is, while a Fourier transform is a different way of representing a function $f(x)$, spherical harmonics are the analogous thing for polar functions $f(\theta, \...
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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 (specifically a Fredholm equation of the second kind). There are many such equations which do have an analytic solution; even some forms of the rendering equation have ...
15
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 rendering you can either loop inside the shader for each light or perform one pass per light and blend the result together (with additive blending).
But things have ...
14
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, but it will give you basic depth of field effects.
The image above, from panohelp.com, shows the basic idea. For each point on the image, there are multiple ...
14
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 hits.
Ambient light tries to solve this problem by shining by a constant amount in all directions. In practice this means that light position or surface normal ...
14
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 interesting properties and operations relevant to lighting that can be performed efficiently. With increasing "order" of SH you can represent higher frequencies (...
14
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 convert it into something we can see.
vec3 colour = vec3(0.5) + normal * 0.5;
The blue colour is because normal maps are supposed to be used relative to the ...
13
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 and model, even in real-time. But the light that is not absorbed will bounce all over the place and cause indirect lighting. This is why for example a lamp will a lampshade will light a whole room ...
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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? This is the light $L(x',\omega_i)$ that some other point $x'$ reflects in the direction $\omega_i$ of point $x$.
Now you have to calculate how much light that ...
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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 ago, assuming it was sRGB was middling but nowadays with DCI-P3 and BT.2020 being very common, it must be ruled out.
The ideal gamut for rendering is the one ...
12
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 point on a sphere is trivial to compute. Put simply, when you know the derivative of the function, you also know the normal.
If your case is narrow enough to ...
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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. But that is of no importance here, we can use that method by adding a rejection clause to it.
In this case you simply want certain parts not to be smoothed ...
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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 samples are taken, this results in both softer specular highlights and softer shadow penumbras: light will be reflected off a surface from a random distribution ...
10
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 all the problems you usually have when you try to project a sphere onto a plane: not all spatial relations in the sphere are well-represented in the plane. If you ...
10
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 isn't really a formula, because the indirect light is dependent on many factors:
Light intensity
Light shape
The BRDFs of the surfaces the light will bounce off ...
10
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 reflections, emissive lighting, or other sources of lighting. The negative lighting from one source of lighting would darken some other source of non negative lighting.
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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 the eye under these conditions.
However, the underlying calculations being done in the shader are at higher precision (e.g. float = 24 effective bits of mantissa)...
9
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 Brian Karis. Also "Lighting of Killzone Shadow Fall" by Michal Drobot is an interesting read on the topic. None of these documents deal with area ...
9
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 flexibility necessary to enable a wide variety of effects and solutions that before were difficult or not possible at all to implement. You can still access ...
8
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 to be environmentally friendly and someone can implement those techniques to varying degrees. The same is for PBR.
In the end, Physically Based Rendering is ...
8
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) and then choose the kernel size based on the sigma. It's a game of finding a kernel size that captures enough of the (mathematically infinite) bell curve to look ...
8
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 as a point in space in a geometrical way. ---> A 3d point can't have normal since it does not have a face.
But the way you should think about it is more like a ...
7
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 deferred lights don't add anything to those pixels (and possibly also mark them in the stencil buffer, to avoid running the lighting shaders on them, for efficiency).
...
7
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 themselves completely black, which isn't true and generally makes corners darker than they should be.
Ideally, you would be using some kind of global illumination ...
7
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. I.e. pixels whose brightness is below a certain (configurable) threshold are are turned down to black.
Downsample and blur the thresholded pixels. Usually, ...
7
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 which is a refractive-reflective/transparent material
you compute and cast two rays from the point of intersection: a reflective ray and a refractive ray
if ...
7
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(l_k)f(l_k,v)cos\theta_{l_k}}{p(l_k,v)}\approx \bigg(\frac{1}{N}\sum_{k=1}^N L_i(l_k)\bigg)\bigg(\frac{1}{N}\sum_{k=1}^N \frac{f(l_k,v)cos\theta_{l_k}}{p(l_k,v)}\...
7
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 if you were to multiply these colors, the object would be fully illuminated and correctly blue (which is the desired product).
The thing with ambient light is ...
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