Implementing Projection Matrix

• gluPerspective

  void gluPerspective(float fovy, float aspect, float zNear, float zFar)
  {
      MGfloat left, right, bottom, top;
      top = fnear * (MGfloat)tan(fovy * 3.1415962f / 360.0f);
      bottom = -top;
      left = left * aspect;
      right = right * aspect;
  
      glMatrixMode(GL_PROJECTION);
      glLoadIdentity();
      glFrustumf(left, right, bottom, top, zNear, zFar);
      glMatrixMode(GL_MODELVIEW);
  }
  

• glFrustum

  void glFrustumf(float l, float r, float b, float t, float n, float f)
  {
  /*
      2n/r-l      0       r+l/r-l     0
      0         2n/t-b    t+b/t-b     0
      0           0      -(f+n)/f-n   -2fn/f-n
      0           0         -1        0
  */
      // OpenGL matrix is column major.
      float m[16] = {
         2n/r-l,        0,          0,  0,
         0,        2n/t-b,          0,  0,
         r+l/r-l, t+b/t-b, -(f+n)/f-n, -1,
         0,             0,   -2fn/f-n,  0 
      };