Widgets are available for separate control of brightness and opacity. This arrangement allows the user to segment the data by making certain ranges of values visible or invisible. The opacity can be adjusted to vary the display from translucent to opaque, the latter being equivalent to an isosurface display. Brightness can be adjusted for a pseudo-lighting effect. The data may be rotated in texture space to be viewed from any orientation.
Results are best if the slicing planes are kept perpendicular to the user's line of sight.
In a stereographic virtual environment, where the user can move in world space, the lines of sight can have any orientation, and the planes must be rotated to remain perpendicular to them. Since the planes can slice the texture volume at any orientation, the slicing polygon vertices must in general be recomputed each animation frame. The ONYX at Argonne is currently equipped with RM4 raster manager boards. These contain 4 Mbytes of texture memory, 2MB of which are usable for the texture itself. Three-dimensional texture mapping on the ONYX currently requires the texture pixel resolution in each of the three dimensions to be a power of two.