Processing: Creative Coding and Computational Art

Figure 13-11. Custom Rotation of a Rectangle Around
the X-, Y-, and Z-Axes example
The 2D array float[][]originalVertices is used to store the original rectangle vertices
data, and float[][]transformedVertices is used eventually to receive the transformed
vertices data, which is then passed to Processing’s vertex() function for drawing. In the
setup() function, I create the original rectangle with the standard sin() and cos() function
approach described in numerous sections of the book. I don’t draw the rectangle
here, but rather construct it in data and assign that data to the originalVertices[][]
array. Next, in draw(), I call some custom rotate functions that update the values of the
angleX, angleY, and angleZ variables used in the rotation calculations. Finally, I call the
createRect() function, which internally calls the rotateVertices() function and draws
the rectangle on the screen. It is in the rotateVertices() function that most of the
sketch’s real heavy lifting occurs.
At the top of the rotateVertices() function I declare three 2D arrays. These arrays are
used to temporarily store the transformed vertices data. To make things simpler (honestly),
I set up the sketch to call the rotateVertices() function every time draw()
executes. This isn’t the most efficient approach, but it avoids things like having to check
which rotation function commands were invoked; I just assume they’re all being called.
However, if you comment out any/all of the following lines:
myRotateX(2);
myRotateY(6);
myRotateZ(3);
the program will still work properly. The rotateVertices() function will still be called
from within createRect(), but some/all of the rotation angle values won’t change, so
you’ll get less or no rotation. Reading though the rotateVertices() function should be
straightforward, even though it’s kind of dense. The important thing to notice is how the
previous array’s values are input into the next set of expressions, and how these expressions
are assigned to one of the temporary arrays. I chose to have the function return the
final array, which is why I used the expression transformedVertices = rotateVertices();
in the createRect() function and created the three temporary arrays (rotatedVertices_
XAxis[][], rotatedVertices_YAxis[][], and rotatedVertices_ZAxis[][]) locally within
3D
641
13