/**
* Set the view matrix `s' is the scaling factor of translating real coordinates to the screen
* coordinates (x0, y0) the screen coordinates of the center
*/
void setMatrix(Matrix3D viewMat, double s, double x0, double y0) {
mat.unit();
mat.mult(viewMat);
mat.scale(s, s, s);
real2Screen = s;
mat.translate(x0, y0, 0);
transformed = false;
}
