Graphics Reference
In-Depth Information
In Cycles, the approach is quite different. All the names of the closures describing surface
properties have a Bidirectional Scattering Distribution Function (BSDF), which is a general
mathematical function that describes the way in which light is scattered by a surface in the real
world. It's also the formula that path tracers such as Cycles use to calculate the rendering of
an object in a virtual environment. Basically, light rays are shot from the camera. They bounce
on the objects in the scene and keep on bouncing until they reach a light source or an empty
background (which, in Cycles, can emit light as well). For this reason, a pure path tracer such
as Cycles can render in reasonable times an object set in an open environment. The rendering
times increase a lot for closed spaces, for example, furniture set inside a room, because light
rays can bounce on the floor, the ceiling, and the walls many times before reaching one or
more light sources.
In short, the main difference between the two rendering engines is due to the fact that,
while in Blender Internal, the materials use all the traditional shader tricks of a scan-line
rendering engine such as the simulated specular component, the Cycles rendering engine
is a path tracer that tries to mimic the real behavior of a surface as closely as possible as if
the surface were real. This is the reason we don't have an arbitrary Specular factor simulating
the reflection point of light on the surface in Cycles, but instead have a glossy shader that
actually mirrors the light source and the surroundings to be mixed with other components
in different ratios. Thus the glossy shader behaves in a more realistic way.
Just for explanatory purposes, in this topic, I will refer to the more or less blurred point of
light created by the reflection of the light source on a mirroring glossy surface as
specularity
.
Be aware that the rendering speed in Cycles depends on the device you use to render your
scenes—CPU or GPU. This means that basically, you can decide to use the power of the
CPU (default option) or the power of the graphic card processor, the GPU.
To set the GPU for the rendering, perform the following steps:
1.
Call the Blender User Preferences panel (
Ctrl
+
Alt
+
U
) and go to the System tab,
the last tab to the right of the panel.
2.
Under the Compute Device tab to the bottom-left corner of the panel, select the
option to be used for computation. To make this permanent, click on the Save User
Settings button or press
Ctrl
+
U
. Now close the Blender User Preferences panel.
