How to get a perfect score

By Johnny Ho

Why get a perfect score?

• Free Gold Medal• Pride

o Beat Gennady Korotkevich 2009-2011: 1st place 2012: 2nd place

• Fameo Get Interviewedo Get mentioned at rallies (but don't go and play frisbee outside

instead)

• GIRLSo Many, many girls will be gazing at your face all dayo You will need a priority queue to handle them allo Johnny Ho has many many girls.

Computer graphics

the actual meeting topic

How to draw a point

• Fill in a pixel:

• *applause*

How to draw on an LCD screen

• Most LCDs come with three channels• Mix the red, green, and blue channels to make

colors

How to draw a line segment

• Imagine the bounding box of the line segment• Take the maximum of the two dimensions• Sweep across that dimension and fill in the

corresponding pixel

• To be lazy, first decompose into triangles• How to draw a triangle:

o Sweep across y coordinate and fill in points that lie within left and right intersection

o Round x coordinates properly to avoid aliasing

How to draw a polygon

• Remember this?• Take advantage of subpixel structure• Calibri 8pt, zoomed in:

o Microsoft ClearType

• ~3x horizontal resolution• Variation in color is largely undetectable by

human eye

How to draw text (very trickily)

How to draw a 3d object

• Again, first decompose into triangles• Give each triangle a color depending on angle

towards light source• How to draw a 3D triangle:• Apply a perspective transformation

o Basically, just divide x and y coordinates by z coordinate to obtain x' and y' coordinates

o Then draw 2d triangle

Demo

• Link• [code not included because of ugliness]• Z-buffering

o Save Z coordinate as well as actual colorso Determine which pixels of the object are closer to camera

• Interpolationo Interpolate between the three points of each triangle to improve

smoothness

Phong shading

• Adds a specular layer• Previously named techniques only incorporate

diffuse• Results in plastic texture

Shadow maps

Soft shadows

Raytracing

Credits to http://users.softlab.ntua.gr/~ttsiod/renderer.html for his amazing renderer/raytracer

Solution to last week's PotWFind # common factors = # factors of gcd

int ans=0, g=gcd(n, m);for(int i=1;i*i<=g;i++) {if(g%i==0) {

ans+=2;if(i*i==g) ans--;}

}return ans;

public int gcd(int a, int b) {return b==0 ? a : gcd(b, a%b);}

PotW

• Go home and search up more awesome computer graphics stuff! :D

• (no, you don't actually get points for this)