9

Event 935
you can visualize the effect you get with spherical
environment mapping. Shrink-wrap wraps the
map around a giant sphere, leaving only one
singularity. Cylindrical is like a g iant c y linder.
TheScreensystemmapstheimagedirectlytothe
view, with no distortion. It’s simi lar to planar, in
that it’s like a giant backdrop hung in the scene.
Unlike the other environment mapping methods,
Screen is locked to the v iew. When you move the
camera, the map moves with it. Therefore, you can
only use it for still renderings, or animations in
which the camera doesn’t move.
To use a b i t m ap w i t h a ny e nv i ronment a l
mapping system other than Screen, you need a
high-resolution map because of the size of the
virtua l sphere, or cylinder.
An environment map is not assi gned i n the
Material Editor, because it’s not applied to the
geometry of an object, but rather to the scene itself.
Environment maps appear in the background, as
seen from the camera or perspective view.
When you assign a map to the environment, it’s
thesameasifyou’dassignedamappedmaterial
to an object in your scene. To edit or adjust the
assigned m ap, you need to place it in one of the
sample slots in the Material Editor. You can do that
in one of two ways:
• Click the Get Material button in the Material
Editor, and then get the map from the scene.
• Put the map from the Environment dialog to
one of the sample slots in the Material Editor.
You can do this by dragging and dropping f rom
the Environment dialog map button to the
sample slot.
Note: To control whether or not the renderer
uses the environment map’s alpha channel in
creating the alpha for the rendered image, choose
Customize > Preferences > Rendering, and then
turn on Use Environment Alpha in the Background
Antialiasing group. If Use Environment Alpha is
turned off (the default) the background receives
an alpha of 0 (completely transparent). If Use
Environment Alpha is turned on, the alpha
of the resulting image is a combination of t he
scene and background image’s alpha. Also,
whenwritingTGAfileswithPre-Multiplied
Alpha set to off, turning on Use Environment
Alpha prevents incorrect results. Note that only
background images with alpha channels or black
backgrounds are supported when compositing in
otherprogramssuchasPhotoshop.
Event
The event is the basic unit of organization in a
Particle Flow particle diagram (page 3–989).There
are two types of events: global (page 3–949) and
local (page 3–963).Abir th event (page 3–916) is a
specialized type of local e vent.
1. Global event
2. Birth e vent
3. Local event
Each event contains one or more actions (page
3–903),whichcanaffectparticlebehavioror