3.6.1 The Appearance Panel
The Appearance panel lets you change most common appearance
properties of the target object.
If the target is an individual geom, then changes you make in the
appearance panel apply to that geom's appearance. If the target is the
World, then appearance panel changes apply to the World appearance
and to all individual geom appearances. (Users have found that
this is more desirable than having the changes only apply to the World
appearance.) If the target is a camera, then appearance panel changes
apply to the geom that was most recently the target.
Figure 3.5: The Appearance Panel.
The five buttons near the upper right corner under the word
Draw control what parts of the target geom are drawn.
- This button specifies whether faces are drawn.
- This button specifies whether edges are drawn.
- This button specifies whether the bounding box is drawn.
- This button specifies whether VECT objects are drawn. VECTs are a type
of OOGL object that represent points and line segments in 3-space;
they are distinct from edges of other kinds of objects, and it is sometimes
desirable to have separate control over whether they are drawn.
- This button specifies whether surface normal vectors are drawn.
The four buttons under Color labeled Faces, Edges,
Normals, and BBox let you specify the color of
the corresponding aspect of the target geom. Clicking on one
of them brings up a color chooser panel.
This panel offers two sets of sliders: H(ue) S(aturation) V(alue), or
R(ed) G(reen) B(lue), each in the range 0 through 1. The square
shows the current color, which is given numerically in both HSV and RGB systems
in the corresponding text boxes.
Figure 3.6: Color Chooser Panel.
In the HSV color system, hue H runs from red at 0, green at .333, blue at .667,
and back to red at 1.0. Saturation gives the fraction of white mixed
into the color, from 0 for pure gray to 1 for pure color. Value gives the
brightness, from 0 for black to 1 for full brightness.
Pressing the RGb or HSV button at top center switches
the sliders to the other color system. You can adjust colors either via
the sliders, or by typing in either the RGB or HSV text boxes.
Click OK to accept the color that you have chosen, or
Cancel to retain the previous color setting.
The SHADING browser lets you specify the shading model that
Geomview uses to paint the target geom.
- Every face of the object is drawn with a constant color which does not
depend on the location of the face, the camera, or the light sources.
If the object does not contain per-face or per-vertex colors, the
diffuse color of the object's appearance is used. If the object
contains per-face colors, they are used. If the object contains
per-vertex colors, each face is painted using the color of its first
- Each face of the object is drawn with a color that depends on the
relative location of the face, the camera, and the light sources.
The color is constant across the face but may change as the face,
camera, or lights move.
- Each face of the object is drawn with smoothly interpolated colors based
on the normal vectors at each vertex. If the object does not contain
per-vertex normals, this has the same effect as flat shading. If the
object has reasonable per-vertex normals, the effect is to smooth
over the edges between the faces.
- Each face of the object is drawn with exactly the specified color(s),
independent of lighting, orientation, and material properties. If the
object is defined with per-vertex colors, the colors are interpolated
smoothly across the face; otherwise the effect is the same as in
Constant shading style.
The Facing Normals button on the Appearance panel
indicates whether or not Geomview should arrange that normal vectors
always face the viewer. If a normal vector points away from the viewer
the color of the corresponding face or vertex usually is darker than is
desired. Geomview can avoid this by using the opposite normal in
shading calculations. This is the default. Using Facing Normals
can give strange flickering dark or light shading effects, though, near
the horizon of a fairly smooth facetted object.
Press this button to use the normals given with the object.
The three text fields in the lower left corner of the Appearance
- Line Width
- The width, in pixels, for lines drawn by Geomview.
- Normal Length
- This is actually a scale factor; when normal vectors are drawn, Geomview
draws them to have a length that is their natural length times this
- Patch Dicing
- Geomview draws Bezier patches by first converting them to meshes. This
parameter specifies the resolution of the mesh: if Patch Dicing
is n, then an n by n mesh is used to draw each Bezier
patch. if Patch Dicing is 1, the resolution reverts to a
built-in default value.
The Revert button on the Appearance panel undoes all
settings in the target appearance. This causes the target geom to
inherit all its appearance properties from its parent.
The Appearance panel's Override button determines whether
appearance controls should override settings in the objects themselves –
for example, setting the face color will affect all faces of objects with
multi-colored facets. Otherwise, appearance controls only provide settings
which the objects themselves do not specify.
By default, Override is enabled. This button applies to all objects,
and to all appearance-related panels.