#### 3.6.1 The Appearance Panel

The Appearance panel lets you change most common appearance properties of the target object.

Figure 3.5: The Appearance Panel.

If the target is an individual geom, then changes you make in the appearance panel apply to that geometry'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.

The five buttons near the upper right corner under the word Draw control what parts of the target geom are drawn.

Faces
  This button specifies whether faces are drawn.
Edges
  This button specifies whether edges are drawn.
BBox
  This button specifies whether the bounding box is drawn.
Vects
  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.
Normals
  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.

Figure 3.6: 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.

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.

Constant
  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 vertex.
Flat
  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.
Smooth
  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.
CSmooth
  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 panel are:

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 number.
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.