87 lines
2.3 KiB
Plaintext
87 lines
2.3 KiB
Plaintext
= Light transport =
|
|
|
|
== Radiometry recap ==
|
|
|
|
What is radiant flux?
|
|
* total amount of energy passing through a surface (measured per second)
|
|
* Radiant flux in Watts or Joules/second
|
|
|
|
=== Why do we not use radiant flux? ===
|
|
|
|
* When we emasure a high flux val, we dont know if lots of energy through a
|
|
small surface, or a little energy through a huge surface
|
|
* TLDR its to ambiguous
|
|
|
|
New unit irradiance
|
|
* Flux per unit area
|
|
* IE Watt/m^2
|
|
|
|
=== Why do we not use irradiance? ===
|
|
|
|
We know the surface, but we still need an angle
|
|
* Could be lost of energy in a huge angle
|
|
* little energy in a small angle
|
|
|
|
New unit Radiance
|
|
* Flux per unit area angle
|
|
* W / (m^2 * radians)
|
|
|
|
== Basic question ==
|
|
|
|
How do we calculate how much light exits a surface point in a given direction
|
|
|
|
[[maxwell_equations|Maxwell equations]]!
|
|
|
|
In practive, we dont do that. We try to think of light as a ray unless we have
|
|
to
|
|
|
|
Instead we use the rendering equation!
|
|
|
|
Terms used in diagrams
|
|
|
|
* V - direction towards the viewer
|
|
* N - surface normal
|
|
* L - vector pointing towards the light source
|
|
* R - reflected ray direction
|
|
* Theta,,i,, and Theta,,r,, - incident and reflected angles
|
|
|
|
To calcuate R `R = L - 2N(L * N)`
|
|
|
|
== Light attentuation ==
|
|
|
|
* The amount of intensity light looses as it travels farther away. Light looses
|
|
energy as well as it reflects off of surfaces
|
|
* How can we calculate attentuation?
|
|
|
|
`L * N`
|
|
|
|
Assuming that L and N are normalized, the attentuation will be equal to
|
|
`cos(theta)` where theta is the angle between L and N. This is true because of
|
|
the dot product.
|
|
|
|
== Materials ==
|
|
|
|
How can we simluate the look of different materials?
|
|
|
|
Based on how they relfect light.
|
|
|
|
* Specular surface reflects exactly one ray
|
|
* One incoming direction
|
|
* One outgoing direction
|
|
* Diffuse spreads ray into smaller rays in all directions
|
|
* On incoming direction
|
|
* many outgoing direction
|
|
* many outgoing intesntiy
|
|
* Spread breaks out the ray into a few smaller rays in a single direction
|
|
|
|
To simulate a surface, we can use a probability density function that takes
|
|
|
|
* incoming light direction
|
|
* point on surface
|
|
|
|
This method will output the _probability of a given outward direction_
|
|
|
|
Something like `probability of happening = f(incoming direction, point, outgoing direction)`.
|
|
|
|
This is known as the _Bidirectional reflectance distribution function (BRDF)_.
|