makeProxyImages(1pf) OpenGL Performer 3.2.2 Reference Pages
NAMEmakeProxyImages - OpenGL Performer tool for generating images for image-
based rendering in which the images are projected on a proxy, a
simplified version of the object
SYNOPSISmakeProxyImages file [ options ]
DESCRIPTION
The program makeProxyImages is one of the tool programs distributed with
the OpenGL Performer high-performance graphics library. It can be used
to create images (views) of the specified object from a set of
directions. Since the images are being projected on a proxy, a
simplification of the original object, additional processing may be
required to add views of parts of the proxy that are partially or fully
obstructed by other parts. These additional texture pieces are important
because as the proxy is rotated away from the view at which the texture
was computed some parts of the proxy that were not directly visible from
the view may become visible. Thus each image consists of the view of the
object and a collection of texture pieces for obstructed parts of the
proxy. It is necessary to store texture coordinates for each proxy
triangle so that the texture pieces are correctly mapped. Consequently,
the program makeProxyImages outputs not only textures storing the views
but also a pfIBRnode that contains the texture coordinates and the proxy
geometry. The proxy of an object can be created using the program
simplify.
The input to the program is the file containg the original complex
object. The file containing the proxy is specified using the switch -pf,
the images are stored in files with the name specified using the switch
-f (a view number and the extension rgb is added automatically), and the
resulting pfIBRnode is stored in a file specified using the switch -pfb.
It is also important to specify the size of the texture (-W xsize ysize)
and the oversampling factor in case the hardware does not support
antialiasing (switch -o). The view directions can be defined using the
text file with information about rings (switch -rv), using only views
around the object (switch -n), or using uniformly distributed 3D views
(switch -nv). Each line of the ring file contains two values: the angle
from the horizontal plane and how many views are created for that angle.
Use the switch -sk if you want to skip a certain number of views in each
ring.
By default the program uses orthographic projection. The center of the
projection is the center of the bounding sphere around the object and the
object is scaled so that the bounding sphere fits the window. If the
bounding sphere is too large you may try to scale up the object using the
switch -s to better use up the texture. You can use perspective
projection by defining the distance of the camera from the center of the
bounding sphere. It is recommended to use the orthographic projection,
though.
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In image based rendering the lighting is captured in the textures thus it
is important you specify the lights the same way as in your scene. By
default the default perfly lighting is selected. You can specify your own
lights using the switch -l (-l posx posy posz posw r g b). Several
switches can be used to define multiple lights.
PACKING ADDITIONAL TEXTURE PIECES
By default the program makeProxyImages renders only the view of the
object, without the extra texture pieces for obstructed triangles of the
proxy. To enable this feature you have to add the switch -ev. The
process has two steps. First, the number and size of texture pieces is
determined and a packing algorithm determines their position around the
primary view. Second, for each view the texture pieces are rendered in
place.
The packing algorithm operates on pixel level and there are several
switches that effect its speed and quality of results. To speed up the
packing algorithm you can downsample the textures before packing using
the switch -evd. The drawback is that there may be more wasted space
between texture pieces. You can also reduce the number of neighboring
pixels the algorithm checks when finding optimal place for texture pieces
(switch -evp). In general, the texture pieces are not aligned with their
neighboring pieces, thus when the view texture is mipmapped the gaps
between the textures may become visible. For this purpose you can add the
switch -evmp and set how many mipmapping levels will be without any
cracks. What happens is that each edge of the texture piece that is not
a silhouette edge is extended to contain more pixels from neighboring
triangles. Setting the value too high may cause the packing algorithm to
fail.
If the packing algorithm fails to place the texture pieces around the
primary view the object is scaled down a little (for the given view) and
the algorithm is restarted. This repeats until all texture pieces fit.
Similarly as obstructed triangles may come into full view also backfacing
triangle may become visible as the proxy is rotated away from the view.
Thus it is possible to add texture pieces for backfacing triangles into
the view texture using the switch -bf. Not all backfacing triangles are
added but only those that may be visible from neighboring views. Since
additional texture pieces that are used for backfacing triangles of the
proxy can be found in neighboring views it is advantageous to combine
several views into a single texture. This reduces the number of texture
pieces packed into a texture for one view. You can use the switch -tm to
control this. It is recommended not to exceed 2K x 2K when combining
several views into one texture.
FINETUNING TEXTURE RENDERING
When rendering additional texture pieces you can control how far before
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and after the proxy triangle the clip planes are being set. This option
affects triangles around the silhouette of the object (this is view
dependent, for each view there are different triangles that contain the
silhouette of the object). Since the proxy fully contains the original
object parts of the silhouette triangles may be transparent. This may
cause visible cracks when the object is rotated. Moving the clip planes
reduces some of the cracks.
If you move the plane that is behind the triangle further away (switch
-evlb) some of the geometry that is behind the silhouette is included in
the texture. When you move the front clip plane closer to the cameras
(switch -evlf) some of the geometry that is in front of the silhouette is
included in the texture.
Since some proxy triangles may have texture with transparent edges it may
be desirable to sort the proxy triangles. Since the proxy can be viewed
from any direction it is necessary to determine how the triangles are
sorted. If the proxy is rendered with selecting only the nearest view
the triangles are ordered for each view differently. You have to set that
mode using the switch -nr. By default, three or four nearest views are
blended together. In that case the proxy triangles are sorted for each
group of views. Sometimes it may be possible to see changes in
transparency as the view moves from one group of views to another. If
this becomes too obvious you can disable the sorting using the switch
-evns.
All the issues mentioned in this section can be drastically reduced if
the proxy is very close to the original object - especially around
visible sharp edges - or if the number of views is increased.
NOTES
To obtain the full set of command line options run the program
makeProxyImages without any parameters.
If your machine does not support a single-buffered visual with at least 8
bits per red, green, blue, and alpha component the images may be missing
alpha channel. See the number of alpha bits printed at the beginning of
the makeProxyImages output. On some SGI systems with multisampling you
may try to use the switch -nms to request a visual wihout multisampling,
improving the chance of getting a visual with alpha channel.
Do not forget to oversample the textures on machines with no antialiasing
(switch -o).
The process may take very long time if the proxy is very fine and many
texture pieces have to be added to each view. Since the rendering is done
into a window make sure that you do not overlap the window during the
process or that the screen saver does not start. If some of the textures
are corrupt you may restart the program with same parameters and add the
switch -sfr that skips rendering of the given number of textures. It is
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makeProxyImages(1pf) OpenGL Performer 3.2.2 Reference Pages
also a good idea to increase shared arena size (using environmental
variable PFSHAREDSIZE) to avoid memory overflow when the pfIBRnode is
saved at the end.
In case you are inspecting the view textures you may notice that
sometimes the additional texture pieces may intersect the image of the
object. This is fine because those triangles that are overlaped are
assigned one of the additional texture pieces packed around the object.
SEE ALSO
performer, pfIBRtexture, pfIBRnode, simplify
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