VFleet Known Bugs and Work-Arounds

This document lists known bugs and work-arounds for VFleet.

Known Bugs for VFleet Version 1.1

Transfer Function Window Confusion Bug

On some platforms, for example the DEC Alpha under OSF, the mechanism which packs the transfer function control elements into the transfer function window may not work properly. This is a difficulty with Motif. The work-around is to use the Show Debugger Menu button in the File menu to create a Debug menu. The Resize Tfun Dialog item in that menu can then be used to (mostly) straighten out the transfer function dialog.

Rotation Is About Center of Object, Not Center of View

Rotating the dataset using the "track ball" window causes rotation about the center of the volume, even if the camera view is shifted off-center. The only work-around is to change the view using the camera controls rather than the "track ball".

Rendering Artifacts at High Zooms

If camera motion is used to zoom way in to a small number of opaque pixels and trilinear interpolation is turned on, rendering artifacts appear. This is apparently a quantization error problem, and is viewing-direction dependent. This problem can generally be avoided by slight changes in viewing direction. Alternately, don't zoom so far in.

Hither and Yon Planes are Curved

If the hither and yon distances are used to slice through the volume, the cut surfaces will be segments of a sphere in perspective projection mode. This is done to save on rendering time. If this is annoying, possible solutions include using a smaller fovea angle and rendering in parallel projection mode.

Lighting Errors on Flat Surfaces

Lighting errors can occur when rendering large flag surfaces, for example the surfaces of blocks. Work-arounds include turning lighting off and turning trilinear interpolation on.

Mippmapping Sometimes Doesn't Happen

If 3D mipmapping is turned on and the fovea angle is high, VFleet may decide that mipmapping is not needed at the beginning of a ray and then fail to start using it later on when the ray has diverged from its neighbors. This can result in data being "missed" by the rays as they diverge. Work-arounds include using a smaller fovea, using a larger hither distance, and using parallel projection. This problem is not likely to actually occur much.

Mipmapping Doesn't Respect Voxel Aspect Ratio

The 3D mipmapping algorithm assumes that each voxel is roughly cubic. Thus if 3D mipmapping is turned on with a dataset with very non-cubic voxels, artifacts can result. The work-around is to not use this option with such datasets, or to resample the data to have a voxel aspect ratio closer to unity.

Tcl Script Crash Error

Some Tcl scripts, which contain loops that execute very quickly, cause VFleet to crash. This problem is not repeatable, and may in fact no longer occur. If you have a Tcl script that does this in a repeatable fashion, please send it in! Work-arounds consist of making small changes to the script, for example saving the current image to a non-writable location in each loop iteration.

Entering Text in Number Slots of Dialogs

Some dialog entry areas require a number for input. Typing text into these slots can under some circumstances confuse VFleet. The work-around is to not do that.

Opacity Varies for Time Evolutions using Gradient Table Tfuns

The Gradient Table transfer function type produces a voxel opacity which is weighted by the local gradient magnitude, relative to the maximum gradient for the same dataset. This makes the function easy to use, but when doing time evolutions the maximum gradient can change with time. This causes the opacity returned by this tfun to vary, causing the image to fade in and out.

Known Bugs for VFleet Version 1.0

Motif Window Sizing Bug #1

This bug arises in constructing complex transfer functions by loading parts from files into an existing SumTransferFunction. When the new sub-transfer-function of the SumTransferFunction is loaded, the Transfer Function Editor window may not enlarge to show the new parts. The new parts are actually there; they are just not visible or editable. The work-around is to add the new parts, save the whole transfer function to a file, and then reload the whole transfer function (replacing the existing, half-hidden transfer function). This bug will only arise when constructing transfer functions multiple levels deep. (This bug is fixed in version 1.1)

Motif Window Sizing Bug #2

The window size setting options in the Image pulldown menu sometimes fail to produce a window of the currect size. Two work-arounds are possible. The first is to use the menu to set the window size before loading the first data volume. The second work-around is to simply resize the window by dragging the corner of the window frame. The current window size appears in the message displayed when a render is initiated. (This bug is fixed in version 1.1)

Tcl Script Crash Error

Some Tcl scripts, which contain loops that execute very quickly, cause VFleet to crash. This problem is not repeatable, and may in fact no longer occur. If you have a Tcl script that does this in a repeatable fashion, please send it in! Work-arounds consist of making small changes to the script, for example saving the current image to a non-writable location in each loop iteration.

Entering Text in Number Slots of Dialogs

Some dialog entry areas require a number for input. Typing text into these slots can under some circumstances confuse VFleet. The work-around is to not do that.