In this video tutorial, made with Blender version 4.2, we will see how to specify at which points an extruded geometry appears and disappears along a curve in Blender.
Video Transcript
Hello everyone! In this video tutorial, made with Blender version 4.2, we will see how to specify at which points an extruded geometry appears and disappears along a curve in Blender.
This is a feature that allows for creating small animations useful for logos, text, or other special effects, as the parameters can be keyframed, as we will see.
First, we need a Curve object, which can be either Bezier or NURBS, including Path-type curves as well. Let's start with open curves, because there is a small issue with circles that we will examine later.
So, I add a default Bezier curve and modify it slightly, specifically by adding a control point moved to the left. This small editing will be useful later when we look at the different types of value mapping.
After defining the curve, open the Object Data tab in the Properties editor and look for the Start and End Mapping section, which is located within the Geometry section of the tab.
We immediately notice that this section is disabled, so we won’t get any results by changing the values of its parameters.
To enable this section, we need to provide geometry to the curve. This can be done by modifying one of the parameters that gives the curve solidity, such as Geometry Extrude or Bevel Depth.
Depending on your needs, you can choose whether to give the curve a basic profile, such as a segment with Geometry Extrude or a circle with Bevel Round, or a custom profile using Bevel Object.
The Start and End Mapping parameters will now be available, allowing you to decide from which point on the curve the geometry will appear and up to which point it will be shown, using the Start and End parameters respectively.
Note that we are not actually modifying the curve itself, but only the points at which its geometry is displayed. In fact, in Edit Mode, you can see that the curve’s control points are not moved.
If the Start and End points in the panel do not match what you consider to be the initial and final points of the curve, you can enter Edit Mode, select all the curve's control points, and use the Switch Direction operator to reverse the direction of the curve.
The Start and End parameters can be keyframed, making this feature useful for creating animations, such as logos or signatures.
As you may have noticed, the Start and End values are expressed as numbers between 0 and 1. However, it's also possible to change how these values are mapped. For example, you might not want this value range to reflect the resolution of the geometry, which is determined by the U Resolution parameter, but rather another value. The choice is between Segments, which refers to the number of segments, and Spline, which represents the actual length of the curve.
For closed curves, such as Bezier Circle and NURBS Circle, the Start and End Mapping parameters usually don’t work, because a closed curve has no start or end.
It is possible to open a closed curve by deselecting the Cyclic checkbox in the Active Spline section, but this often leads to curve deformations. However, there are some small tricks that allow us to maintain the original shape while using Start and End Mapping.
The first step is to change the control points' handles involved to Free, so that they don’t change their orientation when we disable Cyclic mode. To change the handle mode of certain control points, select those points, press the V key, and choose the new mode, which in our case will be Free.
Disabling Cyclic mode will still introduce a small gap between the starting and ending control points. To solve this problem, I recommend duplicating one of the two control points with SHIFT D, keeping it in the same position as the original, and then connecting it to the other control point.
The connection between the two control points is made by selecting both with a multiple selection, and then pressing the F key.
The resulting shape appears closed, but it actually has a start and an end, allowing you to use Start and End Mapping as desired.
These are the basic pieces of information you need to understand how to map the start and end points of a Curve object with a profile geometry. Now, let's look at how I created the animation I showed at the beginning of the tutorial.
I started with a simple Path curve, which is straight at first, giving it a good number of control points positioned in such a way that they could be moved to follow the profile of the car.
I duplicated and moved the initial Path curve in Edit Mode, so all the segments are actually part of the same object.
Then, I moved the various control points of the curves to make them follow the profile of the car.
Next, I animated the Start and End parameters in the Mapping section of the Path object. Since I duplicated the curve in Edit Mode, all the segments created through copying are affected by the Start and End parameters, achieving the result you saw at the beginning of the tutorial.
Well, I hope this video tutorial was helpful! See you soon!