--------------------------------------------
student    : zxf
graded by  : Damian Isla
problem set: ivscan
--------------------------------------------
Renders 1st test (triangle)   (0-3): 0
Renders 2nd test (rgb)        (0-2): 1
Renders 3rd test (cube)       (0-2): 1
Renders 4th test (interpen)   (0-2): 1
Renders 5th test (ellipse)    (0-2): 1
Renders 6th test (geekball)   (0-2): 1
Exactitude                    (0-2): 1
total                        (0-15): 6
--------------------------------------------
notes:

Your renderer has the serious problem that it crashes when I try and run it on anything. It fails with an assert error in EdgeRecList::NextPolyEdge, which suggests to me that it could be a matter of removing polygon edges too soon.

Besides that, a few smaller matters:

1) You were not correctly intializing the EdgeRec, in that you were
   not correctly adjusting the starting value of X to account for the
   start of the edge being off-pixel-center. i.e. the initial
   value of xcurr does NOT equal xstart, but rather xstart + epsilon
   (finding epsilon is the trick). Because what you REALLY want is the
   value of X at the intersection of the edge with the next scan line. 
   Note that it is not JUST X that should be adjusted in this way, but 
   also color and depth (and inverse depth).

2) Linearly interpolating Z in screen space is wrong. You needed to
   instead use linearly interpolated values of h in order to correcly
   gauge depth.


--------------------------------------------