Lecture 3/3

Final Project

• How to do float number comparison

  The computer represents a float number only approximately, and operations on float numbers will accumulate numeric error.

  When we try to find whether two float numbers are equal, this is the wrong way to do

  if(a == b)
  {
   ...
  }
  

  You should write a function like,

  bool approx_eq(float a, float b)
  {
    return fabs(a-b) < 1.0E-8;
  }
  

  And you you should change the comparison code into,

  if( approx_eq(a,b) )
  {
   ...
  }
  

• What you have to do if you are using non-uniform scaling on your models

  • The problem: lighting does not look right.
  • The solution: enable normalization by adding this line to your init(),

    glEnabel(GL_NORMALIZE);
    

• How to convert a number into a string

  #include <cstdio>
  #include <algorithm>
  using namespace std;
  
  const char* tostring(int var)
  {
    static char buf[100];
    fill(buf, buf+100, 0);
    sprintf(buf, "%d", var);
    return buf;
  }
  

• How to generate a random float number in [0, 1)

  // if you want different rand number series, you should use srand(some_seed).
  // rand() and srand() are defined in stdlib.h.
  float normalized_rand()
  {
      return float( rand() ) / RAND_MAX;
  }
  

---