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gluLookAt() Performance

Started by python_regious Nov 29, 2001 at 4:06 PM 3 replies 850+ views

Original Post

Nov 29, 2001 at 4:06 PM

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

Fruny

Nov 29, 2001 at 4:17 PM

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

  
void GLAPI
gluLookAt(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().