3D Game Programming

}

shape.computeFaceNormals();

shape.computeVertexNormals();

returncenter_points;

}

The main purpose of this function is to find the center of the river so that it,

and surrounding points, can be pulled down. We pull down a shape’s vertices

by setting the z property to a negative number.

In the preceding function we worked through the entire plane, one row at a

time. The first for loop sets the row variable to zero, then figures out where the

center of the river should be for that row. From Chapter 6, Project: Moving

Hands and Feet, on page 59, we already know that Math.sin() makes a nice

winding path, so we use it again here.

The four lines that compute and then recompute the center determine how

many curves there should be, how far the bends are from the center, where

this point is in the current row, and where that point falls in the entire list

of vertices. You should experiment with 4 in the first center line and 0.1 in the

second line. If you’ve already taken trigonometry in school, you know these

numbers represent the frequency and amplitude of the sine wave. Mostly, it’s

just fun to play with them.

We dig a trench in each row and then combine them to form the river. We

start from the center point for each and work our way out to ten vertices on

either side (plus and minus the distance). Last, we store the center vertex in

case we want to use it later as a way to put stuff on the river.

Once all of the rows have had some portion of them dug out, we have to

recompute normals. 3D renderers work hard to keep track of the direction in

which faces and their corners are pointing. This direction is called a normal

and it helps with lighting, shading, and shadows. We don’t have to worry

much about how normals work, but we do need to tell the renderer that we’ve

changed them by telling the shape to computeFaceNormals() and computeVertexNor-

mals().

With that, we have a trench for the river to flow through (see Figure 9, The

River Trench, on page 194).

Next we add the actual river.

Tricking the Eye

Adding the river water and the lid to keep the raft inside the river is pretty

easy for us. We need two planes—one for the water, which will be blue, and

report erratum • discuss

Warping Shapes to Make Unique Things • 193

Prepared exclusively for Michael Powell