Crayola is a Geomview external module used to interactively color OOGL objects. Crayola should appear in Geomview's external module browser automatically after it has been properly installed. If this does not happen, add the line
The buttons at the top of the Crayola main panel state the mode that the program is in. It begins in "Get" mode, meaning that picking an object in Geomview (by moving the cursor over the object in the camera window and pressing the right mouse button) will adjust the colorwheel to show the color of the object at the chosen location. In the Silicon Graphics Iris version, the colorwheel is located on the main panel. Click with the mouse to move the black dot around and change the color selection. The "Intensity" slider is used to make the colors darker or lighter. The slider starts set to the far left, or full intensity. Moving the slider to the right will decrease the intensity, until, at the far right, the color wheel is entirely black. The second slider, marked "Opacity," will be discussed later. In the NeXT version, the color picker panel will pop up seperately (The color picker may be set to use a different color selection mode than the colorwheel).
Colors may be assigned to parts of an OOGL object by clicking the "Set" button on the Crayola main panel and picking the object in the Geomview camera window. The object may not already have color information; if this is the case a panel will pop up asking if you want to add color information to the object. Clicking on "Yes" will modify the object to include color information.
Each OOGL object has a slightly different scheme for representing color. For example, quads are colored by vertex, while polylists may be colored by face or by vertex and Bezier patches are colored by patch corner. See oogl(5) for a detailed discussion of which object uses which coloring scheme. Generally, in Crayola, clicking on a face will color that entire face with the given color, either by changed the color assigned to the face or by changed the color assigned to each of the vertices of the face. If per-vertex coloring is being used, the colors of the vertices may be changed individually by clicking on them.
An entire object may be colored by clicking the "Set All" button and picking it in Geomview.
Color information may be removed from an object by clicking the "Eliminate Color" button and picking on the object in Geomview.
Crayola remembers the last change you made to the object, so clicking on the "Undo" button will get rid of minor mistakes. Note that ONLY the last change is remembered.
Crayola has the ability to assign colors containing opacity information (alpha values) to Geomview objects. However, transparent objects are supported only on some computers (eg Iris GTX's, VGX's, Crimsons, and high-end Indigos). The opacity of the current color may be modified by moving the opacity slider (on the main panel on SGI's and the color picker panel on NeXT's). On Silicon Graphics computers supporting transparency, the colorwheel will fade in and out as the slider is moved back and forth. On NeXTs, the upper right portion of the color in the color well will become lighter. If the opacity slider is in a position other than to the far right, the current color is partially transparent. This information will be assigned to the object along with all the other color information. In order for the given color to look transparent in Geomview, transparency must be explicitely turned on in Geomview (see Geomview(5) for details on how to do this).
Celeste Fowler email: fowler@geom.umn.edu The Geometry Center phone: (612) 626-8304 1300 South Second Street Minneapolis, MN 55454