Cause all of the prey fish to spiral toward the center
Listing 10 shows the beginning of a fairly complicated algorithm that causes all of the prey fish to have a tendency to spiral toward the center of thecluster of prey fish.
| Listing 10 . Cause all of the prey fish to spiral toward the center. |
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for(int cnt = 0;cnt<preyObjects.size();cnt++){
if(preyObjects.size()>1){
//Get the next prey objecttempPrey = preyObjects.get(cnt);
//Find the displacement vector from this prey// object to the preyCenter
tempVectorA = tempPrey.getDisplacementVector(preyCenter); |
The code in the body of the for loop that begins in Listing 10 is executed once during each animation cycle for each of the prey fish in thepopulation of prey fish.
To begin with, the if statement prevents the tendency to spiral toward the geometric center from being applied when there is only one prey fishremaining in the population. I will leave it as an exercise for the student to think about this and to decide whether or not this is a good decision.
The code in Listing 10 gets a reference to the next prey fish object in the population and then gets and saves a reference to a displacement vector pointingfrom the prey fish to the geometric center.
Create a rotated vector.
Listing 11 creates, scales, and saves a new GM01.Vector3D object having the same component values as the displacement vector from Listing 11 , but assigning those values to different axes.
| Listing 11 . Create a rotated vector. |
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tempVectorB = new GM01.Vector3D(
new GM01.ColMatrix3D(tempVectorA.getData(1),
tempVectorA.getData(2),tempVectorA.getData(0))).scale(1.2); |
Once again, I will leave it as an exercise for the student to think about the length and direction of such a vector in relation to the originaldisplacement vector. It might help to begin by drawing some vectors in 2D that swap components and then extending the same thinking to 3D. One thingis for certain, unless all of the components have the same value, the new vector created in Listing 11 has a different length and direction than the displacement vector created in Listing 10 , and that would be true even if the vector from Listing 11 had not been scaled.
Move the prey fish object based on the sum of the vectors
Listing 12 begins by adding the two vectors that were created in Listing 10 and Listing 11 , scaling the vector from Listing 10 before performing the addition. Note that the scale factors applied to the rotated vector in Listing11 is different from the scale factor applied to the original displacement vector in Listing 12 . The ratio of these two scale factors influences the tendency of the prey fish object to move toward the center relative to itstendency to move around the center.
| Listing 12 . Move the prey fish object based on the sum of the vectors. |
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tempVectorA =
tempVectorA.scale(0.9).add(tempVectorB);tempPrey = tempPrey.addVectorToPoint(
tempVectorA.scale(0.1)); |