Depth Cues: Creating the Illusion of Depth - Flash 3D: Animation, Interactivity, and Games - page 21

Figure 2.5 demonstrates another depth cue: interposition, or overlapping shapes. All of
the objects are at the same distance from the screen to your eyes, yet the composition
portrays a sense of depth. Overlapping objects assist in creating this illusion. The red
ball is partially blocking the view of the man. It appears to be closer to the viewer. The
cast shadow also helps establish that the ball's position is in front of the man.

Figure 2.6 Depth perception based on light and shadow

Light and shadows are essential in creating the illusion of three-dimensional space.
Without these two elements, objects would appear flat. Highlights are a result of light
illuminating or reflecting off an object. Shadows exist where the light cannot reach.
Light and shadows differentiate parts of an object that are at different depths. Figure
2.6 demonstrates how light and shadows affect the perception of depth. Both images
are the same. The image on the right has been flipped vertically. Notice what happens
to the highlights and shadows and how depth is perceived. The raised bumps in the left
image become recessed pits in the right image.

Surface shading defines form by giving
an object a three-dimensional feel. In
Figure 2.7 the light is coming from the
left. The highlights showcase the light's
angle and define the red ball's smooth
surface.

The gradient shading across the ball's
surface shows the falloff of light around
the object. It helps illustrate the
object's spherical shape. The illusion
of roundness is achieved through the
curvature of the shadows near the
bottom. The cast shadow underneath
the ball also helps establish where the
light is coming from.

Figure 2.7 Light and shadows