4. Modeling grass

(clicking) Great work! Now we've got all the math we need for a computer program to draw as many lines as we need to create a good approximation to a parabola. Let's return to some of the artistic aspects of grass starting with the width. In this interactive, I can move the points around and I haven't drawn the legs of the control polygon just to make it look a little bit simpler and, let's see, that kind of shape for the spine looks pretty good. So let me move on to the next step which is to define the width. I'm going to do that using something we'll call a Skeleton. The Skeleton is a set of lines, like these, that cut across the blade of grass at 90 degree angles so here's a Skeleton line, here's a Skeleton line and so on. If I connect all the left sides of the Skeleton lines and the right side of the Skeleton lines, I create a region, let me fill that in, and that region looks a lot more like a blade of grass. (click) (tinkling) I can control the width using this slider here so that's just adjusting the length of those Skeleton lines and that width there looks pretty good. Finally, I can control the color. I can go from a deep green to a lighter green to a really light green. Our artists control parameters like this to create the kind of convincing grass that you see in "Brave." Use this interactive to see what kinds of blades of grass you can create and then, in the next video, we'll talk about how to animate it.