Iphone OpenGl ES 1.1: How to modify the camera center from (0,0,0) to (x,y,z)?

Question

For example, center of my object is (1,2,-1). How can i modify the center of opengl es "camera" (center of the coordinates system) from (0,0,0) to (1,2,-1)

If iam not mistaken, gluLookAt is the one to do this but it is not included in openGl es 1.1. Is there any other function that does the same

Do you want to just shift the origin for drawing one object or permanently for all objects, so that you don'y have to shift again and again for other objects? — tipycalFlow, Sep 15 '11 at 07:47
@tipycalFlow yes, to shift for all objects (i have only one). The reason i need this is to be able to rotate the object on 3 axes — alexpov, Sep 15 '11 at 07:52
hmm... see this http://stackoverflow.com/questions/1130520/how-to-change-the-center-of-rotation-in-opengl — tipycalFlow, Sep 15 '11 at 08:52

score 2 · Accepted Answer · answered Sep 15 '11 at 12:22

gluLookAt simply multiplies the current matrix with a well-defined matrix created from the inputs. Its man page contains the formulas you need.

So, for example:

void mygluLookAt(GLfloat eyeX, GLfloat eyeY, GLfloat eyeZ, GLfloat centreX, GLfloat centreY, GLfloat centreZ, GLfloat upX, GLfloat upY, GLfloat upZ)
{
    GLfloat f[3] =
    {
        centreX - eyeX,
        centreY - eyeY,
        centreZ - eyeZ,
    };

    // make f and the up vector have unit length
    GLfloat lengthOfF = sqrtf(f[0]*f[0] + f[1]*f[1] + f[2]*f[2]);
    f[0] /= lengthOfF;
    f[1] /= lengthOfF;
    f[2] /= lengthOfF;

    GLfloat lengthOfUp = sqrtf(upX*upX + upY*upY + upZ*upZ);
    upX /= lengthOfUp;
    upY /= lengthOfUp;
    upZ /= lengthOfUp;

    // use the cross product of f and Up to get s,
    // and the cross product of s and f to get u
    GLfloat s[3] =
    {
        f[1]*upZ - upY*f[2],
        f[2]*upX - upZ*f[0],
        f[0]*upY - upX*f[1]
    };

    GLfloat u[3] =
    {
        s[1]*f[2] - f[1]*s[2],
        s[2]*f[0] - f[2]*s[0],
        s[0]*f[1] - f[0]*s[1]
    };

    // Fill the matrix as prescribed.
    // Note: OpenGL is "column major"
    GLfloat M[16] =
    {
          s[0], u[0], -f[0], 0.0f,
          s[1], u[1], -f[1], 0.0f,
          s[2], u[2], -f[2], 0.0f,
          0.0f, 0.0f, 0.0f,  1.0f
    };

    glMultMatrixf(M);
    glTranslatef(-eyeX, -eyeY, -eyeZ);
}

That's typed directly in here, from the man page. So it's untested but it should be easy to spot if I've made any errors.

Iphone OpenGl ES 1.1: How to modify the camera center from (0,0,0) to (x,y,z)?

1 Answers1