> PS - are their bezier handles?

MoI doesn't have bezier handles - there is actually a problem with the bezier handle type drawing method, which I will try to explain here.

Here is a bezier handle style curve that I drew in Rhino V4:

You can see that the curve is broken up into 3 different sections according to where the handles were located.

The problem is that these sections share tangency, but not curvature. Curvature means how much the curve is bent at a particular point - each section is bent to a different degree at that point, creating a kind of break in curvature at that spot.

Rhino has a curvature graph tool that can help to visualize changes in curvature across a curve, here is what it looks like for that handle curve:



You can see at those points that the curvature does a jump there.

So what does this mean? Well, it doesn't really affect simple matte type shading very much, but it has a much bigger effect on reflections, including highlights.

Here is a rendering with highlights:

You can see that there is a kind of "bunching" effect where the highlight has become stacked up right at that curvature breaking spot. This type of bunching is common in many areas because you also get it on a circular fillet, but a lot of times for smooth curves you might be trying to get a fully smooth effect with them instead of the mechanical-fillet type appearance right in the middle of the curve.

So that's a problem.

Then on top of this, I personally don't quite like the bezier drawing technique too much where you kind of drag out a section and it bulges out a part of the curve behind it... It just doesn't feel quite so natural to me, although certainly the more that you use it the more you can get used to it.


I guess that the curvature break problem gets reduced quite a bit the more points you use in your curve - the more evenly the points are spaced with each other reduces the size of the breaks and they become less noticeable... But they are still there...

So that's why there aren't bezier handles in MoI.

These problems are not really as noticeable on just 2D illustration since you don't get reflections off of those types of shapes. But if you look closely at the shapes you can still often times see the breaks there too if there are a fewer number of points in the curve. I've always been a bit surprised that 2D illustration programs haven't switched to use NURBS instead of the traditional Bezier handles.

There are a lot of CAD programs that go ahead and offer bezier handle curves anyway in addition to the NURBS drawing tools... I suppose I could do that, but it just doesn't seem quite right.

- Michael