The Edit Materials Widget Help
This widget is used to change the way objects look when displayed as
surfaces. It does not affect wireframe or data volume rendering except to the
extent that if they are being viewed simultaneously with some surface data,
then changing the transparency of the surfaces can change how much the
wireframe and volume data is obscured by these surfaces.
In addition to transparency, the color and brightness of each surface
can also be modified. Much of this information, together with the current
default HOME position can be saved to a file by choosing "Write Materials"
from the File menu on the DAVE master widget. It can then be read back in
with the -A option on the dave command line.
The box under this heading displays the object which will be affected when
modifying entries in this widget. By clicking with the left mouse button on
the object name, the name will toggle through all available objects.
Alternatively, picking the right button when over the object name will pop up
a menu of object names to choose from.
There are 4 transparency types, they can be chosen in a manner similar to
that described directly above. The transparency type applies to all objects
displayed as a surface, not just to the object currently selected (unlike all
other controls on this widget). The 4 types are:
None: All objects are totally opaque.
Screen Door: This is the fastest of the transparency modes, but does not
give the highest quality rendition.
You should use this method if you will also have volume data up
at the same time.
Blended: This may give higher quality images than Screen Door, but is slower.
Sorted Blended: This will usually give the best transparent images but can
be considerably slower than the other 3 types.
If the "Transparency" control (see below) is set to 0.00 the object will
not appear transparent regardless of which transparency type is chosen.
When viewing transparent surfaces in conjunction with wireframes and
data volumes certain "approximation tricks" are used. Therefore the
resulting images may not be completely accurate. Different tricks are used
for the 4 different transparency types, test them all out to see which works
best with your data.
There are alternatives to making a surface transparent. You could change
it to a wireframe. You could also clip the surface (see Object Clipping from
the Object Properties menu in the Edit Object widget).
For all of the remaining controls, the double arrows change the value by
.10 and the single arrows by .01. The longer the mouse button is held
down the more the value is changed.
A setting of 0.00 means this object is totally opaque. As soon as this
value is nonzero its transparency also depends upon the Transparency Type set.
A Transparency of 1.00 is totally transparent.
Changing an object's color
An object's color when viewed depends upon several factors.
First, the color of the illumination affects the perceived color. Thus
by changing the color of the front light (Edit Front Light menu item) the
perceived color of all surfaces in the scene will change. Similarly for the
inside colors of all surfaces vis a vis the back light color.
Typically to change an object's color I just modify the Diffuse color
components (see below).
Second, the object can emit light (like a light bulb). This is controlled
by the the Emission settings. The red, green, and blue components can each be
set separately. Increasing this is one way to "brighten up" an object; this
can be especially useful in stereo mode since the glasses cut out some light.
This third component of object color is probably the one most people think
of as an object's "color". It is the color the material appears when
illuminated by white light. Thus, these are the settings you will most likely
want to modify. An example: suppose the red setting is .80, the blue is .50
and the green is .30. Then 8016500416060f the red light which is incident on the
object will get reflected and hence will be seen (absorbed light is not seen by
the observer). Similarly for the other components. Note also: changing the
green and blue settings will not affect the appearance of the inside color of
an object since it is illuminated by a red light (assuming the default setting)
and thus there are no green or blue components to reflect anyway.
The overall brightness of the diffuse component of the reflected light also
depends upon the orientation of the surface with respect to the light source.
The more perpendicular the surface is to the light source direction the
brighter the reflection. Thus, a sphere will appear brightest in the "center"
and dimmer towards the "edges" (assuming the default position for the front
This controls the ambient or "background" light reflection. Unlike the
diffuse settings the brightness of this component of reflected light does not
vary depending upon the orientation of the surface relative to the light
source. Thus a sphere which only had an ambient component would appear as a
uniformly colored circle, no shading would be present. Since shading is an
important visual cue for understanding surface orientation and shape, it is
usually a good idea not to have the ambient settings very high. On the other
hand you probably want them nonzero otherwise surfaces close to 90 degress
away from the viewer will appear almost totally black.
Sometimes objects exhibit "highlights". These bright regions are due to
the direct reflection of a light into a viewers eyes. This occurs when the
angle from the light to the surface is the same as the angle from the surface
to the viewer. These settings control the strength of this effect. I am not
sure if they ever have an affect given the data structures DAVE uses to
describe objects, try it and see.
This controls how shiny the surface appears (like the matte vs. shiny
finishes for photographs). I'm not sure I've ever seen it make a difference,
try it and let Larry know if it does.
In the old days, long long ago, you had to click on this to actually have
the changes made in any of the settings take effect. Nowadays you shouldn't
have to do this, you should see the changes immediately. If you don't see a
change when you change the settings, I suppose you could try clicking on this
button. At least you'll feel like you're trying. If this does make a
difference, let us know.
Copyright 1995 by Lawrence M. Lifshitz and the University of
Massachusetts Medical School. All rights reserved.