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# gluLookAt() Performance

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4 replies to this topic

### #1python_regious  Members

Posted 29 November 2001 - 10:06 AM

I was wondering whether there is a performance benefit of translating and rotating the scene manually over using the above function?

### #2Fruny  Moderators

Posted 29 November 2001 - 10:17 AM

Here the code for gluLookAt, from SGI''s Sample Implementation

  void GLAPIgluLookAt(GLdouble eyex, GLdouble eyey, GLdouble eyez, GLdouble centerx, GLdouble centery, GLdouble centerz, GLdouble upx, GLdouble upy, GLdouble upz){ int i; float forward[3], side[3], up[3]; GLfloat m[4][4]; forward[0] = centerx - eyex; forward[1] = centery - eyey; forward[2] = centerz - eyez; up[0] = upx; up[1] = upy; up[2] = upz; normalize(forward); /* Side = forward x up */ cross(forward, up, side); normalize(side); /* Recompute up as: up = side x forward */ cross(side, forward, up); __gluMakeIdentityf(&m[0][0]); m[0][0] = side[0]; m[1][0] = side[1]; m[2][0] = side[2]; m[0][1] = up[0]; m[1][1] = up[1]; m[2][1] = up[2]; m[0][2] = -forward[0]; m[1][2] = -forward[1]; m[2][2] = -forward[2]; glMultMatrixf(&m[0][0]); glTranslated(-eyex, -eyey, -eyez);}

So, if you don''t need the normalizations and have combined all you rotations in a single matrix, you MAY be a little faster, otherwise go for simplicity and use gluLookAt().

### #3python_regious  Members

Posted 30 November 2001 - 12:21 AM

Thanks I think I''ll stay with gluLookAt().

### #4Maximus  Members

Posted 30 November 2001 - 02:09 AM

I see no problem with just using glTranslatef and glRotatef without matrices

### #5Fruny  Moderators

Posted 30 November 2001 - 02:49 AM

quote:
Original post by Maximus
I see no problem with just using glTranslatef and glRotatef without matrices

Gimbal lock ?
Ease of use ?

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