I have been toying around with three.js these days, and may continue doing so until I have a solid collection of posts on it. So it should go without saying that I am going to end up writing a few posts on Materials such as the standard material, and features of materials such as emissive maps. So then today I am going to be writing about a Mesh material known as the Lambert material, which is one of many options for skinning a mesh, and in this post I will be getting into this one a little to get a better sense of what it is all about compared to the many other options.
If you are just getting started with three.js you might be familiar with at least the Mesh Basic Material, and that you use a Material with a Geometry to make a Mesh object instance to which you can then add to a scene object. However you might now be interested in working with lights, and having a material that will respond to a light source. If so the Lambert Material may be of interest as this is one option that will work with light while the basic material will not. The main material that I would use more often than not would be the standard material, but the Lambert material might prove to use a little less overhead then that material by loosing accuracy when it comes to lighting. So lets take a look at this material, and maybe some additional topics of interest surrounding it that may apply to materials and threejs in general.
The source code examples I am writing about in this post can be found on my test threejs github repository.
There are materials in three.js that do not respond to a light source, and then there are materials that do respond to lights, the Lamber Material is one of several options that do respond to a light source.
From what I have gathered this is one of the faster solutions for having a reflective material that will respond to a light source. If you are interested in knowing why, you might choose to read more about Lambertian reflectance and Gouraud shading.
I often like to develop on systems like a raspberry pi that only has so much resources to work with when it comes to memory and CPU overhead. So I tend to try to keep my models very low poly, and also make use of materials such as the Lambert material to make better use of what I have to work with on platforms such as this. However overall it might still be better to go with the standard material in some cases.
First off the Lambert material needs a light source. If you use the material without any light source shining on it, and you have a black background, you may end up staring at a black screen. So before we get into the material, lets just take a moment to touch base a lights just for a moment.
There are many lights to work with in three.js, but in this demo I will be using a spot light. This is a directional light that casts out light in the shape of a cone, it can also be used to case shadows. The spot light inherits some things from the base Light class, and the Light class inherits from Object3D which means I can move it around, and work with it just like a camera, or any other object in three.js. However the Object3D.lookAt method will not work for changing the direction of the spot light, to change that you will need to use the target property of the spot light.
I could get into spot lights more, but this post is on the Lambert Material, so that will have to wait for another day.
When I first wrote this post I was using threejs version r91, and the last time I came around to do a little editing I was using r127. Always be mindful of what the version of threejs is that is being used in examples on the open web, threejs moves very fast with development, more so than many other projects. So code breaking changes come into play all the time, as such I have got into habit of mentioning what version I was using when I first wrote a post, and also when I edited the post last.
For a simple example I put together a scene containing a cube, and plane both of which use the Lambert material. In order to see anything though I also added a spotLight, and positioned it away from the cube, and plane. This is because when it comes to just using the color property that will set a solid color for the material, but I will only see anything if there is a light source shining on it. There is getting into other properties such as the emissive property, and also using an ambient light source but for now maybe I will save that for another section later.
This results in reflection in a manner that is expected with light reflecting from areas where the spotlight is striking the surfaces of the cube, and plane.
Unlike materials like the basic material, the Lambert Material does not just have a single color for filling the faces of an polygon. There is a color that is shown when it is effected by a light source, and then there is a color that it is by default regardless if there is any light or not.
To set the color value that is not effected by light you will want to set the emissve property of the Lambert material, and use the color property to set the color that is to be reflected when effected by a light source.
for example say we add the emissive property to the material that I gave in the plain to this:
This will make all the area of the plane that is not effected by the spot light a shade of gray, rather than the default which is black. In addition to being able to set the emissive color, the intensity can also be set from a 0 to one value, it is also possible to define a texture that will modulate with the emissive color using the emmsiveMap property. To set a texture that will function as the regular color map, you will want to use the plain old map property.
The Lambert Material is a good first choice for having a material that responds to light, but depending on the project it might not be the best. The good point of it is speed, but not so much accuracy, even the Standard material seems to do a better job in that regard.
I would not sink to much time into getting into the details about each material though. In the long run what I really want to do is figure out what i really want to do with threejs when it comes to making actual projects. As long as I do a decent job of keeping my code easy to read it should not be to hard to switch from Lambert to standard materials and back again.