Mirroring and Reordering Polygons

If you have a symmetrical object, it's often easier to construct one half of the object, then flip and paste a copy onto the original half to make the whole shape.

The following example uses a simple shape to illustrate the principles of mirroring. To try it yourself, first create a cone, turn it into a PEP object, then enter the PEP editor. See PEP Modeling if you don't already know how to do those activities.

  1. Once you've got the cone in the PEP editor, select all its polygons. (See Selecting Polygons for more information.)

  2. Copy the polygons by pressing Ctrl-c or by choosing Edit > Copy from the menu bar.

  3. Place the PEP Jack in the scene at the base of the cone. To do this, press the PEP Jack button on the PEP palette:


    Drag the mouse in the scene. An outline of the PEP Jack follows the cursor. Release the mouse to place the PEP Jack. You can also click and drag the PEP Jack after you've placed it.

  4. Shift-drag the PEP Jack's scale handle (the white cube) toward the tip of the cone.

    Tip: If you're having a hard time selecting the white cube, try this. Place the mouse cursor over the scale handle. When the cube turns orange, hold down the right mouse button, then press Shift. If you accidently deselect the polygons, press Ctrl-z one or more times to undo your mistakes.

    The PEP Jack displays purple arrows indicating a constrained scale:




  5. Continue to Shift-drag past the cone's bottom plane. This inverts the cone, as shown here:




    This movement also results in a negative scale--the inverted cone's coordinates become negative and the vertices have a different ordering from the original. This causes a problem which you'll fix in the next step.



  6. While the inverted polygons are still selected, press the Reorder Polygons button, found on the PEP palette:


    This fixes the negative scale problem described in the previous step. If you don't reorder the polygons after pasting back the original, you'll have two objects with different orderings. The result is that the polygons in one of the cones are culled the wrong way, so you see the inside of the cone.

  7. Paste the original object in it's original position by pressing Ctrl-v or by choosing Edit > Paste from the menu bar. The cone looks like this now:



  8. The final object is a single PEP object consisting of 2 mirrored sides:



    The object would have looked like this if you hadn't reordered the inverted cone's polygons: