writeup.txt

CMU CG 15662 Assignment 2.0

Checking point:
I implemented erase_vertex(), erase_edge(), flip_edge(), split_edge(), collapse_edge(), bevel_face(), bevel_face_positions() functions.

erase_vertex(): key point is to go through every edges, halfedges and faces that connect the deleted vertex, map all those faces
to a single face, and to track every edge in a loop connect this vertex, only keep those edge not directly connects vertex and delete
those directly connected edges and halfedges, finally adjust the halfedge's next().

erase_edge(): find two vertices that connect this edge, change their halfedges, and also change the halfedges whose next() is deleted halfedge
to it's twin's next().

split_edge(): only apply to edge that belongs to triangular, not working in more than 3 edges. First find the center point of the edge,
explore the v->halfedge()->next()->next()->vertex() and v->halfedge()->twin()->next()->next()->vertex(), and connect the center point with
two found vertices separately. 

flip_edge(): use next to explore target edge's connected edges, find two adjacent halfedges(one from the halfedge() side, one from 
the halfedge->twin() side), which contains the vertex next to the targe edge's two endpoints.
Connect two found vertices and delete the original two.


Final:
I implemented triangulation(), linear_subdivision(), catmull-clark_subdivision(), loop_subdivision().

triangulation(): fix one vertex, and take two adjacent edges to generate a triangle, and use one of new generated edge with the second_Halfedge->next()
to make the next triangle, iterate until meeting the end.

linear_subdivision(): this one is quite straightforward, and the most of functions are already given by the halfedge.h, loop around 
and set the center it each new_pos.

Catmull-clark_subdivision(): similarly to linear subdivision, except that edge and vertex's new_pos has more weighted calculation, the center()
function can simplify the code a lot here.

loop_subdivision(): one issue I stuck quite a while is to deal with optional type, I wanted to exclude the case where split_edge doesn't
return valid split and instead return optnull, but it seems the usage of optional is a bit obscure, but it seems that if the system
detects optnull, it will finish the manipulation, so that even though I called split_edge inside the loop_subdivision function, it still 
can break the rest of loop_subdivision code. The main part is in the loop of split edge, we need first cache the current edge and next edge,
so that even though split_edge creates new edge and change the order of edges, we can still find the original next edge to iterate, otherwise
the program will stuck to somewhere it can't finish the loop.


CMU CG 15662 Assignment 3.0

Checking point:
1. Camera Rays completed, step1-3 finished, one important note is that matrix multiple vector doesn't result the correct vector transformation,
instead we should calculate the vertex of the vector separately and then recalculate the vector in new world-frame.

2. Intersection completed, both triangle and sphere function are finished, note that for sphere part, inside the sphere function, the frame is sphere 
itself, i.e. the center of the sphere is (0,0,0), and the function is x^2+y^2+z^2=R^2, don't forget R is squared.

3. implemented bbox() and hit() function, hasn't finished the build and hit in bvh.inl yet.