extrusion tutorial

This tutorial shows how to extrude around current view axis and applies an envelope so extrusion and deformation are applied simultaneously.
Home address for source code of meditor is:
Create a circle from first button on objects window and that looks like as:
As I want to create extrusion around an axis so I give a "radius" from real center of world. I change to select mode and I move whole mesh rightwards as in next image:
I want a hollow object and I want to discard new triangles inside the object, so I change to edit mode and I select that vertex as in next image (use left hand side mouse button):
To move that selected point, just push "m" to move and move mouse rightwards. That should look as:
I change the view using "d" key. This is the view which I want to extrude circle around. That should look as:
I want to select points which I want to extrude and certainly extrusion should maintain the links. One could select each point using left hand side mouse button but for last command I selected the only point which will not be extruded, so I use Alt+"enter" to invert selection and all unselected points will turn selected now and that selected point is now unselected as:
Once I have selected points which will be extruded, I will select the service to be applied. Launch command window using "g" key and push "actions" button. That looks as  next image. I will push the fifth button from "extrude around" service. This label "extrude around" has several services and one could try them as exercise.
If correct button was pushed, main window should appear as:
One should notice, that unselected point was exactly as one should expect, no service was applied but I want delete it now. We DON'T DELETE IT BEFORE because links are checked by the extrusion service. If one deletes the links, extrusion will not work as expected because no triangles exist. Next image shows I selected that unwanted point.
In edit mode, just push "del" button. In this mode, del is applied on selected points. This should delete that selected point ONLY. As the extrusion could produce duplicated points, one should also use "backspace" to delete duplicated points. This will lock the main window a little and no operations are working for while. After lock is disabled, double points were deleted and that looks as:
The number of fat or slim parts are controlled by theta and phi. Initial values are 1 and 1, so this produce the previous shape. Try different values of phi, just push "*" key and change value to 3.
Normals can be wrong oriented. Just push "n" to see normals. Use "M" command to correct normals. Sometimes normals appear pointing to inside and looks as:
Just correct it. Change to select mode and push F5. This will flip normals for whole mesh. Now the object is complete. If one uses F4 (unselect all), that looks as:
If one applies material and pushed ALT+F10, the shaded image appear in main window and it looks as:
That is all folks!