3.7.7 Cont3 sample

Function cont3 draw just usual contour lines but at slices of 3D data. The sample code is:

int sample(mglGraph *gr)
{
  mglData c;  mgls_prepare3d(&c);
  gr->Title("Cont3 sample");  gr->Rotate(50,60);
  gr->Alpha(true);  gr->SetAlphaDef(0.7);
  gr->SetOrigin(0,0,0); gr->Axis("_xyz"); gr->Box();
  gr->Cont3(c,"x"); gr->Cont3(c); gr->Cont3(c,"z");
  return 0;
}