TeraRecon, Inc.
Real Time Visualization

June-25-2001

=======================

Software Postwarp using the VLIPlus library

The VLIPlus library provides a software postwarp for the VolumePro500.
The software postwarp may be used alone, generating a bitmap, or with
the included display capability. These allow the  VolumePro500 to be
used in environments where hardware acceleration of OpenGL is not
available or is otherwise undesirable.

Both VLIPlus and the example, spinner, are structured such they can be
used on both Microsoft Windows and X windows. However, only the Windows
version is being made available at this time.

INSTALL VLIPLUS
================
Unzip vliplus.zip and double click VLIPlus\setup.exe

This will install :
VliPlus.exe and vliplus.dll in c:\progran files\Volumepro\bin 

Following include files in C:\Program Files\VolumePro\inc

VLIPlus.h
VLIPlusContext.h
VLIPlusDisplay.h
VLIPlusDisplayNT.h
VLIPostWarp.h
VLIPlusExport.h
VLISWPostWarp.h

              
vliplus.lib in C:\Program Files\VolumePro\lib

and example source files in c:\program files\Volumepro\VLIPlus\Spinner.

Build environment :
Spinner is set to build with Microsoft Visual C++ 6.0.
You have to have VolumePro_SDK Version 2.1 installed on your system to cpmpile this program.

Postwarp

The software postwarp uses a bilinear filter to map the baseplane output
of the VolumePro500 to a postwarped bitmap. The performance and accuracy of this postwarp depends on the CPU:

On an Intel Pentium III and above a highly optimized bilinear filter
is used. This runs far faster than the standard filter but with a
reduced precision. Sub-pixel accuracy is limited to 1/16 of a  pixel in
X and 1/8 in Y. This precision may show artifacts with larger zoom
factors. For example,  displaying a 32x32x32 volume at 512x512x512 will
be visibly different from the full precision filter.  The RGBA
calculation is always done in full 8888.

On other x86 CPUs -- or on Pentium III systems that do not permit
the Pentium III extensions to be used -- a less optimized filter is
used. However, this filter runs at full precision. A Pentium II, or 
equivalent, is recommended as a minimum.

NOTE: To use the general x86 routine on a Pentium III processor,
override FilterScanlinePIII in CVLISWPostWarp to call FilterScanline.

Performance on non-x86 processors is unsatisfactory and is therefore not
supported.


Display

VLIPlusDisplay provides a simple mechanism to output the output of
the postwarp to the display. On Win32 (VLIPlusDisplayNT) this uses GDI
using 32bit DIBs. On systems with an 8bit display  (for example
hi-resolution monochrome displays) an 8bit DIB is built from the green
channel from  the image and displayed using the system palette. (Use a
gray scale system palette for best  results in 8bpp.)


Spinner

A sample application, spinner, is supplied to demonstrate how to use
the software postwarp and display capabilities as well as provide a
mechanism for testing the postwarp and  display  performance.

In all the following, filename refers to a vox file, with the
.vox extension. Hitting q always ends the program.

Spinner may be used interactively:

	spinner filename

Drag with the left mouse button to rotate the volume. Drag with the
right mouse button to change the window/level. Hold down the shift key
and drag horizontally zooms the image in and out.

To run a standard animation:

	spinner filename -a [n]

By default this runs 128 frames. Specify a frame count, n, for
different lengths. 0 indicates indefinite. The animation repeats after
128 frames. An averaged frame rate is output once spinner  ends.

To disable the display but still perform the postwatrp:

	spinner filename -a [n] -nd

To disable the postwarp and display:

	spinner filename -a [n] -nw

Comparing the output of these three -a options indicates the
relative performance of the display and postwarp.

Any of the -a options also accepts a -sb flag to force single
buffer mode. By default animations are double buffered.

Other options are available. Run spinner with no arguments to see them.

Spinner is structured with a portable core (spinner_window) and platform
specific interfaces, such as spinner_window_nt for Win32.


Line drawing support

VLISWPostwarp in VLIPlus has the ability to draw alpha blended lines on
the post-warped image using the DrawLine32bpp method. This is not
currently optimized and has limited performance.  The xxxx_NoFP methods
are not currently implemented. 


Steps to perform a simple postwarp and display

To postwarp a baseplane and display the result perform these steps:

Prior to rendering, construct the VLIPlus objects. See 
Spinner_window::CreateDisplayConductor().

For each frame you can have VLI plus handle the process ('automatic
mode') or perform the steps manually. See spinner_window::Render().

In automatic mode:

CVLIPlus::Render()

Otherwise:

1) CVLIPlus::Render()
2) CVLISWPostWarp::PrepareCanvas()
3) CVLIPlus::Fetch()
4) CVLIPlus::WarpBasePlane()
5) CVLIPlus::OnSync()
6) CVLIPlusContext:Release()

In either mode this is then followed by:

CVLIPlusDisplay->OnPaint()



ay->OnPaint()