Processing: Creative Coding and Computational Art

PROCESSING: CREATIVE CODING AND COMPUTATIONAL ART
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and screenY(). The model functions return the 3D coordinates in model space, which
means the coordinate values after they’ve been transformed (rotated, scaled, and/or
moved), but before they’re projected to the screen. In contrast, the screen functions
return 3D coordinates in relation to screen space. If you’ve never worked in 3D, this may
sound pretty confusing. Remember, computer-generated 3D simulates space, as everything
really lives on the 2D screen surface. To simulate real space, geometry must be
shifted around to give the illusion of perspective, depth layering, and so forth. The actual
3D coordinate geometry we generate ultimately has to be mapped to the space of our 2D
screens, taking into account any perspective calculations. This concept is most abstract in
reference to the z-axis, which doesn’t really exist at all on the screen. Yet, when we work
in 3D, geometry is calculated at specific locations on this illusory axis. To visualize the concept
of screen coordinates vs. model coordinates, think about the classic one-point perspective
image of railroad tracks receding into the distance to a point. In reality, of course,
the tracks remain parallel and never actually converge—which you can think of as their
model coordinates (the actual geometry). But visually, the receding tracks are no longer
parallel, and these illusory coordinates can be thought of as their screen coordinates.
Material Properties
The Material Properties section includes four functions:
shininess()
specular()
ambient()
emissive()
These functions control how object surfaces interact with the light in the scene. For example,
glossy and reflective surfaces have concentrated areas of light, sometimes referred to
as hotspots; think about the small, intense light spots on the surface of an eyeball, or how
light reflects off of a highly polished piece of chrome. This light phenomenon is referred
to as specularity. The specular() function controls the color of these hotspots.
Ambient light, on the other hand, refers to more general and overall lighting—think about
the light in a dense forest or in a room without a direct light source. The ambient() function
controls the color of the ambient light. Like the other rendering attribute functions,
the material functions affect the rendering state as well as the light functions. Once a
material function (e.g., shininess()) is called, its influence will be felt by all future surfaces
created in the scene, until another explicit call to the material function (using different
rendering attributes) is made.
To give an example that involves the Lights, Camera section of the API, I developed a 3D
flythrough sketch that utilizes a lot of the features I’ve been discussing. (This is another
complex sketch that I put in more for inspiration and pleasure than your edification—but
it is cool, and will still be useful for you to take apart and experiment with.)
The example (shown in Figure A-14) utilizes two images that need to be put within the
sketch’s data directory. The images need to be named ground2.jpg and metal2.jpg, and I
recommend making them around 400 by 400 pixels. If the example runs slowly on your