Doc:Manual/Modelling/Curves/Curve Taper

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[edit] Curve Taper

Taper is a scaling effect where the scaling is controlled by a curve. The tool is used on bevelled or extruded objects. As with Extruding, Tapering is “activated” by entering the name of a curve in the TaperOb field on the Curve and Surface panel.

The taper curve defines the width of the extrusion along the curve on the “Bevelled Object” that is defined in the BevOb field. The taper curve is typically horizontal, where the height (local Y coordinates) denotes the scale being applied. If a point on the taper curve goes above 0, on the local Y axis, enlargement occurs. If a point on the taper curve goes below 0 then shrinking occurs. Think of the taper curve as changing the volume of the bevelled object.

For example we can taper a simple curve circle extruded object using a taper curve. Add a curve, exit Edit mode, add another one (a closed one, like a circle), call it “BevelCurve”, and enter its name in the BevOb field of the first curve (Editing context F9, Curve and Surface panel). We now have a pipe. Add a third curve while in Object mode and call it “TaperCurve”. Adjust the left control-point by raising it up about 5 units.

Now return to the Editing context, and edit the first curve’s TaperOb field in Curve and Surface panel to reference the new taper curve which we called “TaperCurve”. When you hit enter the taper curve is applied immediately with the results shown in (Taper extruded curve).

Taper extruded curve.

Taper solid mode.

You can see the Taper curve being applied to the Extruded object. Notice how the pipe’s volume shrinks to nothing as the taper curve goes from left to right. If the taper curve went below the local Y axis the pipe’s inside would become the outside which would lead to rendering artifacts. Of course as an artist that may be what you are looking for!

In (Taper example 1) you can clearly see the effect the left taper curve has on the right curve object. Here the left taper curve is closer to the object centre and that results in a smaller curve object to the right.

In (Taper example 2) a control point in the taper curve to the left is moved away from the centre and that gives a wider result to the curve object on the right.

In (Taper example 3), we see the use of a more irregular taper curve applied to a curve circle.

[edit] Important rules to consider

• Only the first curve in a TaperOb is evaluated even if you have several separated segments.
• The scaling starts at the first control-point on the left and moves along the curve to the last control-point on the right.
• Negative scaling, (negative local Y on the Taper Curve) is possible as well. However, rendering artifacts may appear.
• It scales the width of normal extrusions based on evaluating the taper curve, which means sharp corners on the taper curve will not be easily visible. You’ll have to heavily level up the resolution (DefResolU) of the base curve.
• With Cyclic curves (those curves that connect to form a solid object), the Taper curve in TaperOb acts along the whole curve (perimeter of the object), not just the length of the object, and varies the extrusion depth. In these cases, you want the relative height of the TaperOb Taper curve at both ends to be the same, so that the cyclic point (the place where the endpoint of the curve connects to the beginning) is a smooth transition.