This section is designed to show you how to get MPIRE up and running, render an image, change the view, save an image, and exit using the AVS module interface. Details regarding the individual parameter controls can be found in MPIRE Interface Parameters Reference .

Starting MPIRE

The process of rendering an image of volume data using the MPIRE AVS module interface is as follows.

Running renderd

Log onto the desired render host and determine if at least one copy of renderd is already running. If it isn't then go to the directory containing the executable and type "renderd &". As long as at least one copy of the daemon is running, any number of users will have access to the MPIRE rendering engines installed on that system.

Loading the MPIRE Module

The MPIRE module is an AVS subroutine designed for use in a data flow network. It is loaded and manipulated through the AVS Network Editor subsystem.

After starting AVS, enter the network editor by selecting the Network Editor option from the main AVS panel. This causes the Network Editor and Module Interface panels to appear. Note that the Network Editor panel in the center of the screen is where AVS networks are assembled, while the Module Interface panel on the left side of the screen is where the widgets associated with the modules will appear.

Go to the Module Tools menu by selecting the Module Tools option from the main Network Editor menu. Doing so brings up a submenu containing various options for reading in individual modules and libraries of modules. Select the Read Module(s) option from the Module Tools submenu which brings up a directory browser window. Go to the directory on your system where the MPIRE module is stored, and load the MPIRE module by selecting its name in the browser. This causes the MPIRE module to appear at the top of the Data Input module list in the top half of the Network Editor window.

Constructing a Simple MPIRE Network

Now that the MPIRE module has been loaded, an AVS network must be constructed to indicate to AVS how you would like to use it. The following describes how to use the MPIRE module in a very simple AVS network. For more information describing the use of AVS modules and the construction of AVS networks, please refer to the AVS Users Guide.

Drag an instance of the MPIRE module out onto the workarea (the lower half of the Network Editor panel). Doing so causes the MPIRE interface to appear in the Module Interface panel. Drag an instance of the display tracker module from the Data Output module list onto the work area. Connect the MPIRE output port to the input port of the display tracker module. Make the output port of display tracker visible and then connect it to the input port of the MPIRE module. The resulting network should look like:

Switching Between Interface Panels

The MPIRE and display tracker modules have a number of widgets associated with them. The interface for the currently selected module is highlighted in the Module Interface panel on the left side of the screen. Switching between interface panels is accomplished by selecting the corresponding button in the list at the top of the Module Interface panel.

Rendering an Image

Once an AVS network with the MPIRE module has been set up, rendering an image is as simple as loading a parameter file which describes the initial values to give to the MPIRE widgets.

Selecting a Parameter File

The nature of the AVS widget event handling facilities is such that modules are executed each time the value of a widget is modified by a user. For this reason the initial values of the MPIRE widgets are set based on the values contained in a parameter file, and then made available to the user for modification.

Before loading a parameter file, select the freeze button. Doing so will give you the ability to check the values of the initial parameters before they are sent to the render host for use. Select a parameter file using the read parameter file browser under the read parameters from a file option under the main MPIRE menu.

Next, verify that the render host parameters are set correctly by selecting the set parameters interactively option under the main menu and then the resources option. Verify that the render host and PE group size (for single processor SGI systems this value should be set to "1") values are correct. Finally, deselect the freeze button to start the rendering process. When completed, the render host returns an image which is displayed in the display tracker output window.

Note that the rendering process is composed of three steps including shading, rendering, and compositing. The first of these includes the process of reading your data from disk and requires the most time (perhaps a few minutes depending on the size of the dataset). However this step is only executed when changes are made to parameters describing characteristics of the raw data, and the position of the light source. All other changes result only in the execution of the rendering and compositing steps, and should require no more than a few seconds for the generation of an updated image.

Changing the View

The display tracker module allows you to manipulate your view of the volume by using the mouse to control a virtual trackball. With the mouse pointer in the display tracker window, press and hold the middle mouse button. Doing so will display a bounding box superimposed over the rendered image. You can rotate the bounding box by moving the mouse. Once you have acheived the desired rotation, release the mouse button and a new image will be rendered based on the updated view. You can translate the bounding box (and hence the volume) by moving the mouse pointer in the image window with the right mouse button depressed. You can scale the bounding box by moving the mouse pointer in the image window with the shift key and middle mouse button simultaneously depressed. Finally, you can reset the view to the default by placing the pointer in the image window and pressing the left mouse button.

Saving an Image

In addition to using the MPIRE module in this simple AVS network, it can also be used with a variety of other AVS modules. Using the MPIRE module with modules which accept the image data it outputs allows for such functions as the postprocessing of the images, creating animations, writing the images to a file, and more.

To save a rendered image to a file, drag an instance of the write image module from the Data Output listing onto the workarea and connect its input port to the output port on the MPIRE module. The resulting network should look something like the following:

Use the browser in the write image module interface panel to navigate to an appropriate storage location and select a name for the image file. Note that each time the image is updated, the new image is saved over any previous image in the specified file. For this reason, disconnect the write image module immediately after the desired image has been saved.

Exiting MPIRE

In preparation for exiting AVS, the MPIRE module can be shut down in the same way as any other module. The simplest way is to drag it on top of the hammer in the lower right corner of the work area. Doing so causes the MPIRE module and its interface panel to disappear, and a signal to be sent to the render host executable causing it to exit. Depending on the configuration of your local site and the amiability of your local system administrator, you may also wish to kill the renderd daemon on the render host. Note however that renderd does not use any measurable percentage of CPU time and may thus be left running for future rendering sessions without impacting the render host.