During the client initialization (Tcl/Tk initialization), a .pvrrc is read and can overwrite any system default. After that, the client is free to open as many sessions as needed. Each session is created with a pvr_session command. The following commands open up a session called :brain, and start up a connection with parallel machine named paragon, and load a data set in a partition of 34 processors:
pvr> pvr_session :brain
pvr> :brain open paragon
pvr> :brain partition 34
pvr> :brain dataset cell.slc
At least one session has to be created, as this is the only way to access a parallel machine. Session names must always start with a ``:'' mimicking Tcl/Tk hierarchical convention. After a session is created, it can be controlled by issuing :session_name commands.
The open command is used to open up a connection (Currently, only TCP/IP connections are allowed.); dataset is used to load a data set into the session; partition specifies the number of processors to be allocated. The system has defaults for everything with the exception of the data set name. The data set can be either local (and will be transmitted over the communication channel) or can be specified as a path on a remote machine file system.
Before rendering, the user has to specify the medium onto which the image sequence is to be displayed. The system provides a simple mechanism where a photo widget can be used to display incoming images. The image window command provides an interface to this end; while using the image file command saves all the images directly to a disk. A special handler can be specified to be executed at the arrival of each image (image callback). This mechanism is very general and is currently being used for bookkeeping.
Two basic rendering primitives are available, one for rotations ( render rotate), and another for translations (render translate). These functions generate sequences of transformation matrices that are fed to the session. The session renders the requests and returns an ordered sequence of images back. Other rendering options include changing transfer functions, which are easily specified as an array of values, that are interpolated to obtain a complete look-up table. Other rendering primitives can be added to the system.