The Curve class is the base class for several core threejs Classes to create a Curve in space. There is then a Cuve class prototype method called the get point method that can then be used to get any point along a curve in the form of a Vector3 object, or Vector2 object for 2d curves, by passing a zero to one value as an argument. For the most part thus far I have been using curves as a way to define paths than can then be used to set the position of object3d objects over time such as mesh objects, and cameras. I have also been using curves to get vector3 objects that can then be passed to the look at method to set the rotation for objects also. However I have not yet got into using curves as a way to define the position attributes of custom buffer geometry objects which is what this post will focus on.
There are both easy, and not so easy ways of making a gometry from a curve. When it comes to 2D curves there is creating a shape object, and a Shape or Extrude geometry can be made from that. There are also ways of making a 3d shape from a 2d curve by using the Lathe Geometry class. However there is also of course 3D curves as well and using them to help in the process of creating a cusotm geomerty from the ground up.
There is a lot to be aware of when it comes to curves in threejs, so it might be a good idea to check out my main post on curves in general. There is taking the time to write a custom curve class of need be, and maybe there are some situations in which that will just need to be done. However I have found that for the most part I can do jjst about everything that I want to do with curves by just using the built in Quadratic Bezier Curves class, which is what I will be using in this post.
There is not just stopping here when it comes to learning the basics and beyond when it comes to creating and updating geometry over time in threejs. I have my main post on buffer geometry in general, and the main starting point when it comes to learn a thing or two about making custom geometry would be to start with the position attribute. There is starting out by just making a blank geometry, creating a non indexed position attribute, and then using that with THREE.Points, or THREE.Line.
The source code examples that I am writing about in this post can be found up on my Github at my test threejs repository. This is also where I part all my other source code examples for my many other blog posts that I have wrote on threejs over the years.
When I first wrote this blog post I was using r146 of threejs. Code breaking changes are still made to the core of threejs all the time. I do what I can when it cokes to editing my threejs content to keep it current, but I have wrote a lot of posts and it might be a long time until I come around to this post again.
There is starting out by making one or more curves and then just finding a way, any way at all to make a position attribute for a buffer geometry. When first starting out there is just having the position attribute alone, that might not work well with Mesh objects, but be good enough for Point or Line objects. So in this section I will be going over a few examples that just have to do with doing just this by making use of any and all Curve and Buffer Geometry class features to do so. I will then leave the more advanced examples that have to do with making a full geometry that will work with mesh objects for later, more advanced sections of this post.
There is a get points method pf the curve class that when called will return an array of Vector3 objects along the path of the curve. The count of the number of points will differ depending on an argument that is given when calling the get points method. This is not to be confused with the get point method that will return just one Vector3 object by way of a given 0 to 1 value. I would generally prefer the get point method over the get points method as it allows for more flexibility. However when it comes to making a fairly simple hello world typo example of making geometry with curves this would be a good place to start.
Although the get points method of th Curve class, and the set from points method of the buffer geometry class are nice tools there are not the end all solutions for this sort of thing. In fact when it comes to really getting into how to go about making geometry this way the get point method is what I would want to use to have a better degree of control when it comes to creating an array of vector3 objects, or better yet an array of numbers that I can then use to directly create a position attribute. Speaking of doing so in place of using the set from points method in this example I will be using the set attribute method and create an buffer attribute that will be passed to it that is create with an array of data that is the position data created from, you guessed it a curve.
There are a wide range of options for making a geometry from a 2D path actually. For one thing when it comes to THREE.Points, and THREE.Lines there is just using the setFromPoints method of the Buffer geometry to do so. However there is also creating a THREE.Shape object and then using that with THREE.ShapeGeometry or THREE.ExtrudeGeometry. Yet another option would be to make use of THREE.LatheGeometry which is one way to go about making a 3D geometry from a 2D Curve. So in this section I would like to touch base on some of these options when it comes making a geometry with 2D curves.
There is using a 2D curve to create a Shape, after which that Shape can be used to create a geometry with THREE.ShapeGeometry.
Now that I have some of the basics out of the way with this sort of thing I think that it is now time to have at least one if not more examples In which I make a full Mesh object friendly custom geometry using Curves to create the position attributes. There is a lot to be aware of when it comes to this sort of thing, so I will not be getting into detail with the various types of attributes of buffer geometry so forth.
For this example I am using the Quadratic Bezier Curve class in core threejs to create two curve objects both of which have start, end, and control points to create an update a buffer geometry. The goal here then is to first create the state of the position attribute by pushing in x,y, and z values for points along the curves, and to do so in a way in which the points stagger from one curve to the other. There is the order in which the points that are added that is important, however maybe what is really important is the state of the index that I will be making for this geometry as well as this will be an index geometry that I am making here.
While I am creating the array of numbers of the position attribute I am also pushing in values for another array that I will be using for the uv attribute while I am at it. Once I have my position and uv arrays of numbers set up just the way I want it to be I can then use them to set the attributes for the position an uv attributes of the buffer geometry.
I got the basics out of the way, and I also got some of the not so basic stuff out of the way when it comes to making full custom geometry with curves. But there is still always more to write about when it comes to these sorts of things. I think it should go without saying that what is really cool about curves is not just using them to create a fixed static geometry, but also using them to update the state of geometry overt time as well. So in this section I will be writing about examples that have to do with both creating, and updating geometry over time using one or more curve objects to help with the creation of the position attribute.
So like with just about almost every post that I write on threejs I like to make at least one if not more videos to embed into the blog post along with all the writing and source code examples. So with that said I made this example that is based on the custom geometry example that I made for my mesh friendly geometry section. I made a lot of changes to the source code with this one though by taking a lot of what I worked out and made a few helper functions in an effort to make things more fine grain. Also I wanted to have a function that will just create and return an array of numbers that is the position data values, not just for the sake of creating the geometry to begin with, but also to be used to update the state of the geometry as well.
That will be it for now when it comes to making geometry from curves in threejs, at least until I come around to edit and expand this post a little. I might also want to make one or more threejs project examples posts in which I explore this topic a little deeper as I am sure there is a whole lot of directions I could take this when it comes to making custom geometry this way. That is not to say that I do not all ready have some threejs protect example ideas that are based off of the use of Curve objects all ready. I do have my curve module that threejs example that I started all ready which might be a good thing to check out if you want to read even more about curves.