Learning Processing: A Beginner's Guide to Programming Images ...

When using the OPENGL mode, you must also import the OPENGL library.
14.3
Vertex Shapes
Translation and Rotation (in 3D!) 233
Th is can be done by selecting the SKETCH ➝ IMPORT LIBRARY menu option or by manually
adding the following line of code to the top of your sketch (see Chapter 12 for a detailed explanation
on libraries):
import processing.opengl.*;
Exercise 14-2: Run any Processing sketch in P3D, then switch to OPENGL. Notice any
diff erence?
Up until now, our ability to draw to the screen has been limited to a small list of primitive twodimensional
shapes: rectangles, ellipses, triangles, lines, and points. For some projects, however, creating
your own custom shapes is desirable. Th is can be done through the use of the functions beginShape( ) ,
endShape( ) , and vertex( ) .
Consider a rectangle. A rectangle in Processing is defi ned as a reference point, as well as a width and height.
rect(50,50,100,100);
But we could also consider a rectangle to be a polygon (a closed shape bounded by line segments)
made up of four points. Th e points of a polygon are called vertices (plural) or vertex (singular). Th e
following code draws exactly the same shape as the rect( ) function by setting the vertices of the rectangle
individually. See Figure 14.5 .
beginShape();
vertex(50,50);
vertex(150,50);
vertex(150,150);
vertex(50,150);
endShape(CLOSE);
beginShape( ) indicates that we are going to create a custom shape made up of some fi g. 14.5
number of vertex points: a single polygon. vertex( ) specifi es the points for each vertex in
the polygon and endShape( ) indicates that we are fi nished adding vertices. Th e argument “ CLOSE ” inside
of endShape(CLOSE) declares that the shape should be closed, that is, that the last vertex point should
connect to the fi rst.
Th e nice thing about using a custom shape over a simple rectangle is fl exibility. For example, the sides are
not required to be perpendicular. See Figure 14.6 .
stroke(0);
fill(175);
beginShape();
vertex(50,50);
vertex(150,25);
vertex(150,175);
vertex(25,150);
endShape(CLOSE);
fi g. 14.6