Update for 10-11-22 20:30

tech/light_transport.wiki

@@ -32,3 +32,55 @@ 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)_.