For this tutorial I will have the worded directions along with the exact keystrokes it takes to get the step done. If you are fluent enough with Blender you may not have to look at the keystrokes line. Each step within the keystrokes line will be highlighted like this: Example
. Arrows will indicate that you should be following a menú path.
Usually I try to refrain from making tutorial that have been done over and over again. Grass is a very popular topic for tutorials but in many cases I find that the tutorials are lacking in explanation or don't tell you anything more than throwing it on the plane. They leave it up to the user to spend the time to search and try to figure things out for themselves. Well, luckily for you, I write my tutorials a little differently. I like to tell you more than just the bare bones steps. Anyways, let's get started with it.
Alright, let's get the bare basics down here. This is the stuff you will find in most tutorials that go over grass/hair/fur in Blender. I'll assume you have Blender opened up and ready to go. If you have the default cube, we are going to keep it, if not, add a cube to the scene. Hair in blender is made through the particle system, so what we want to do is add particles to the cube. To do this we want to go to the Object settings, into the particles buttons, and add particle to the cube.
Select the cube; F7 (Object settings); Go into the particles buttons; Clik "Add New";
In order to make the particles appear as hair we only have to change one more setting. Right under the field that displays the name of the particle system there is a drop down selection. Clik on that and you should see that one of the selections is labeled "Hair". At this point, nothing should appear in the main screen. What you have to do is change one of the many settings for the particle system we just added. Let's start out by changing the Normal setting to 0.100, and the random setting to 0.100. Let's alos change the Amount to 5000 and segments to 2. I alos like to turn on Random and Even, but that is more of a personal preference. That'll give us a very basic scene.
Change particle type to "Hair"; Change Normal to 0.100; Change Random to 0.100; Change Amount to 5000;
Change Segments to 2; Turn on Random and Even;
If you render your image right now, something that looks like floating needles will appear. This isn't exactly hair or grass. Let's change a few settings so that we can get this to look a little better. The first thing we need to fix is the fact that our hair is floating. To fix this, we just want to go into the particle settings and within the Visualization box there is a button with the word "Emitter" on it. If you select that, our emitter will appear when we render. Then we want to add some color to this. Go ahead and add a material to our cube. You can edit your material in any way you like. I am just going to make my hair a light grey color and I will turn down the specularity to make it look better.
Clik on "Emitter"; F5 (Shading Buttons); Go into Material Buttons; Clik "Add New"; Edit your material;
There you go! You now know the basics of making hair (or grass or fur) on an object.
Spicing it up
Now that you know the bare basics, I'm going to fill you in on some other things that can be done with your hair. The first thing that you should know is that you can do just about anything in terms of materials and textures that you can do with any other object. While it is fairly simple and intuitive to just throw up a texture and make the hair the color that the texture is on the emitter, it is a little less intuitive to have each hair strand have its color change as it goes from the root to the tip. Below is an image of what I am talking about.
For the most part, doing this sort of thing is done by changing a bunch of different settings in a texture that you add to your hair. Let's get started. Since we already have a material for our hair, let's add a texture. Once you have done that, go into the texture buttons. Under "Texture Type" you will want to select "Blend". In the settings that pop up, clik "Flip XY" and, this isn't necessary, but I like to change "Lin" to "Quad". Then under the colors tab and clik on "Colorband" and change the gradient as much as you want.
Clik "Add New" texture; Change Texture Type to "Blend"; Clik "Quad" and "Flip XY"; Clik "Colorband" and edit it;
Now we need to go bak to your material buttons. In the "map input" box, change "Orco" to "Strand", "Flat" to "Cube", and in the second row of the XYZ rectangle of buttons, change "Y" to "X". After you change those settings, you should be good. When you render you should be able to see that each strand of hair will change color as you go from the surface of the cube to the outer tip.
Go to the "Map Input" box; Change "Orco" to "Strand", "Flat" to "Cube", and in the second row of the XYZ rectangle of buttons, change "Y" to "X";
Another good thing that I would like to point out are the Strand settings, specifically made for hair. If you look at the "Links and Pipeline" box, you should find a grey box labeled "Strands". In the settings that pop up when you clik it, you can change the starting thickness, ending thickness, shape, and a few other things. Rather than going over them, I suggest that you change some settings yourself and find out what they all do. The only thing that I don't like about it is that every time you want to see the changes you make you have to take your mouse off of the popup box and the preview image will update when the box disappears.
Ok, that was just some pretty stuff that you can do, but still quite important in my opinión. Let's get to something else you may be looking for. Let's say you only want your hair to emit from a certain part of the cube or whatever object you are using. For this, let's make it so that the hair only comes out of the top of the cube. I only know of two ways to do this and that is with a texture and with vertex groups. I like doing vertex groups mainly because that means I don't have to make a texture just for it. However, the drawbak is that you cannot get as detailed with vertex groups as you can with a texture. Anyways, here is what we are going after:
In order to make this worque correctly, we need to go into edit mode and subdivide our cube a bit. Otherwise, we will have some hairs that are going down the side. The reason this does this is that the hairs do not stay within the boundary of vértices, but stay near them. With some more vértices, we can better control where the hair appears. I hit the "Subdivide" button in the "Mesh Tools" box 3 times. To make the vertex group that we need, I selected the faces on the top of the cube that do not touch the edge of the cube.
Subdivide your cube 3 times; select the top faces, except the edges (see below);
Now that you have your faces selected for your vertex group you want to actually assign those faces to the group. In the editing buttons and in the Link and Materials box, there is a little section for vertex groups. Clik on New and then clik on Assign. This will assign the selected vértices (that are connected to the faces you have selected) to the new group you just made. If you go out of edit mode and into object mode, you should find that all of the hair is being emitted near the vertex group.
F9 (Editing buttons); Clik "New" vertex group; Clik "Assign"; Go to Object Mode;
Of course, you can easily expend upon this concept and choose any vértices that you like and put them into a vertex group. They do not have to be connected to each other for it to work. You could just as easily make a splotchy cube as well:
Playing with your hair
Here's the last thing I am going to go over here about your hair. You can do quite a bit by just changing the settings that are available in particle settings but there are plenty of things you are not able to do with just those settings. If you go to the Particle buttons there is a button in the particle system box, there is a button that says "Set Editable". Once you have that set up, rather then going into Edit Mode, you want to go into Particle Mode. Clicking that button allows you to manually adjust the vértices just like you would any to any mesh.
Go to Particle Buttons; Clik "Set Editable"; Go to Particle Mode; Edit your hair;
Ok, so I admit, editing your hair in with the usual editing controls isn't that great. But there are some fantastic controls available. In Particle mode, there is a menú selection of "Particle" if you clik on that, one of the selections in there is "Particle Edit Properties". All of the settings there allow you to easily edit the hair and many of the brush settings are pretty self explanatory. I suggest just messing around with the brush types to get a hang of them.
Particle Mode; Particle-->Particle Edit Properties; Play with the brush;
While being able to do this is great for getting a certain result, there is something you need to watch out for. Once you start editing, you cannot change any other particle settings without losing all your changes made while in particle edit mode. If you want try to change something that would cause this, Blender will warn you by saying "Hair is Edited!". If you do decide to get out of the particle edit mode, clik on "Free Edit", the same button that allowed you to edit the hair.