Finish writeup

assignment-1b/writeup.md

@@ -57,14 +57,24 @@ decreases in brightness when all other factors remain constant.
 
 ## Varying $k_d$
 
-TODO
+$k_d$ is the strength of the diffuse component. It also affects an object's
+diffuse color, but at a strength that's affected by how much of it faces the
+light. Much like the dark side of the moon, the parts of the object that aren't
+pointed at the light will not receive as much of the light's influence. In the
+image below, I varied $k_d$ between 0.2 and 1. Note how the part pointed to the
+light changes the strength of the brightness as all other factors remain
+constant.
 
 ![Varying $k_d$](examples/kd-demo.png){width=360px}
 \
 
 ## Varying $k_s$
 
-TODO
+$k_s$ is the specular strength. It uses the object's specular color, which is
+like its reflective component. When there is a large specular $k_s$, there's a
+shine that appears on the object with a greater intensity. In the image below, I
+varied $k_s$ between 0.2 and 1. Note how the whiteness of the light is more
+reflective in higher $k_s$ values as other factors remain constant.
 
 ![Varying $k_s$](examples/ks-demo.png){width=360px}
 \
@@ -74,7 +84,8 @@ TODO
 $n$ is the exponent saying how big the radius of the specular highlight should
 be. In the equation, increasing the exponent usually leads to smaller shines. In
 the image below, I varied $n$ between 2 and 100. Note how the size of the shine
-is more focused but covers a smaller area as $n$ increases.
+is the same intensity, but more focused but covers a smaller area as $n$
+increases.
 
 ![Varying $n$](examples/n-demo.png){width=360px}
 \
@@ -142,9 +153,21 @@ are away from the eye.
 
 ## Shortcomings of the model
 
-The model cannot be used to represent TODO
+The Phong formula is just a model of how light works, and doesn't actually
+represent reality. There's not actually rays physically escaping our eyes and
+hitting objects; it's actually the other way around, but computing it that way
+would not be efficient since we would be factoring in a lot of rays that don't
+ever get rendered.
+
+Also, one needs to take care to use reasonable constants. For example, if using
+a different specular light color than the diffuse color, then it may produce
+some bizarre lighting effects that may not actually look right compare to
+reality.
 
 # Arbitrary Objects
 
+Here is an example scene with some objects that demonstrates some of the
+features of the raytracer.
+
 ![Objects in the scene](examples/objects.png){width=360px}
 \