Since some people have emailed me for explainations, I have decided to added a sample file for this tutorial get it here, it shows the basic concept at work.
Creating cg hair in 3D is a difficult task, the most common approach uses geometry surface with texture mapping. There are a few disadvantages to this method, that makes it difficult to work with. First of all to to tweak the look of your hair requires repainting texture maps, and to control the form requires careful planing and placing each geometry piece. So why Paint Effects? Pfx is a very effective tool suited for creating hair, it gives you ultimate control on exactly how you shape your hair, with no texture painting/alpha maps and lesser time to setup. Changing the looks of your hair can be done on the fly with instant feed back. It is very faster to render, takes very little memory. The render that appears on the above image will take no more than 30 seconds on a 1Ghz machine. "Did you say 30sec!?" "Yes I did", "But I heard in the Final Fantasy Movie it took ..xxxxx amount of days with xxxx machines and xxx mount of people...." Haha...I was only joking this is nothing compare to FF of course, but with performance(speed) to quality ratio, Paint Effects can prove very effective, just read on and I shall you how.
Part 1: setup
First you'll need to have a clear vision of what kind of hair you want for your character, otherwise you'll find your self tweaking endlessly in Maya without any satisfaction. If the image of the hair you want is not in your head then its best to work against a image plane of a photo or sketch. OK so you have a head of some character, we need to make that surface live and draw curves on top of the skull. If you have a subd surface just convert to poly for makelive. Select the head, Modify->Make Live, Create->CV curve tool, start from the back and middle of the head to the front. This curve determines where the hair splits, check my reference for how long this should be. Now EditCurves->Rebuild curve , rebuilt it to uniform and around 9 spans, degree 3. You should also turn on show CV for the curve, you are going to need this often in this tut. You should assign this command to a hotkey,like Cntrl-Alt-V, rename this curve to hair_split_curve01. Now select the curve, Duplicate then move the two curves apart a little so that mid line of the head is in between the two curves(below)rename the second curve hair_split_curve02. Also draw a small curve between at the front of these two hair_split curves, so they join. Doesn't have to be too accurate, 2 spans should do(below). Lower and scale these 3 curves so they are borrowed inside the head.
Part 2: hair control curves
We are going to draw a series of curves that roughly resembles how the hair should flow. Select the head, Make Live, CV curve tool, start off by snapping the first point on to the front CV of hair_split_curve01. Then place about 4-6 CVs on the side of the head(left). The number of CV should be as little as possible while still able to give enough control to shape your hair later on. You can start off a bit more and then delete the CVs later on if the controls takes too long to tweak. Continuously place new curves this way snapping the start of the each new curve to the CVs on the hair_split_curve01. This way the main hair_control_curve are evenly spread, and will result better optimization for paintfx later on. If your hair_split_curve01 has 9 spans you should end up drawing 9 to 11 hair_control_curves on one side of the head. Now select first hair_control_curve and move the CVs out from the head, so they don't intersect with the head.
Tweak the CVs on this curve so they take the shape of your hair in that region.(i.e. front, side). Now tweak all the CVs of the hair_control_curves, so they don't intersect and take on the shape of your hair. Take your time, the better resemblance of your hair you achieve here with few curves/CVs the better look/optimized paintfx will perform later on. I' would say spending a good 30min tweaking will be while worth it :) check the images below for reference. After tweaking them Group the hair_control_curves and Duplicate to the other side Then tweak a little to make the difference between the two sides. Now draw the curves the same way for the front hair_split_curve, so that you have a some hair control curves for the front. 3 curves would be good, make sure those curves looks continuous to the curves control curves on the left and right side.(More below)
Part 3: Power of Pfx
Now we are ready to make some hair! Go to the visor and open up the *brushes/hair/ folder and select a hair brush that mostly resembles your hair design. If you have followed my hair design then select the hairRed1.mel(right, make sure its highlighted). We are going to base on this brush to start off, select hair_split_curve01, PaintEffects->Curve Utilities->Attach Brush to Curves, this will create a new brush for the the stroke hair_split_curve01, and some hair of course. Don't worry if the hair looks like lightning strikes. Rename the new stroke to hair_side_stroke01(outliner), and the new brush to hair_side_brush. If you select the stroke in the outliner and bring up attribute editor. Check the brush tab, there's a load of sliders here, don't be put off by it, its categorized well so you don't have to access many settings that's not required here, I'll go through all the ones that requires to design our hair :) We'll need to adjust the Global Scale according to the size of the head, you can see I have 0.150, but that is my character is at 8cm tall. You should adjust this so that the hair looks very short. If your character is 160cm then leave the Global scale at 3. This is your over all pfx brush scale setting. Open Brush Profiles and look at the Brush Width, this will resemble the how wide our hair emits grows from the hair_split _curves, set it to 0.8, just don't make it too low otherwise your hair will look too flat. Leave the rest of the slider default, oh yeah ignore those other tabs on my screenshots.