Architectural_Design_with_SketchUp

Chapter 5 Rendering in SketchUp
Finally, as you likely have observed multiple times before, light has the tendency to become
dimmer the farther away we are from its source. Imagine looking along a street with street
lamps at night. This effect, called attenuation, means that light particles can’t travel forever—
they lose energy the farther they travel. (See Figure 5.47 for an example.)
As you can see in this brief description, materials and particularly surface qualities like
color, reflectivity, and refractivity have a large impact on how light travels and how our natural
environment becomes visible to our eyes or a camera lens.
Photorealistic rendering software must be able to re-create these physical phenomena
as accurately as possible. If we want our renderings to look like photos (or even better), then
the software must be able to represent all of the aforementioned light and material properties
as realistically as possible. However, it must be able to do that in a time frame that
we as the users can live with. As you can imagine, any computational simulation of complex
natural behaviors can be extremely resource-intensive. Therefore, rendering software is
often designed to take some shortcuts that approximate the “correct” solution just to keep
computation time low. It is a measure of good software that it is able to create high-quality
renderings in a short amount of time.
So how does rendering software work? Without getting too deeply into the technical
details, it is fair to say that it basically works like nature, in that it uses light particles that travel
through space. Depending on the computational approach, however, it may be more efficient
to send out these particles “in reverse” from the viewer’s eye (i.e., the camera view), instead
of from the light sources. Sometimes a combination of both techniques is used.
When these particles meet a surface, the software queries the surface material’s properties
and modifies the particle’s color, direction, and intensity to reflect the material’s absorptive, reflective,
or refractive properties before sending the light particle back on its way. (See Figure 5.6.)
Figure 5.6: Ray-tracing light particles from the viewer’s eye
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