I found very useful to have a control whether osgView::setCameraManipulator does or does not reset camera to home position.
I extended method signature as follows:
void setCameraManipulator(osgGA::MatrixManipulator* manipulator, bool resetPosition = true);
keeping the current usage intact (default parameter), while enabling user to disable the position reset. That can be useful in the situation when manipulator position was already loaded, for example from a file (user specification), or defined any other way, while we do not want to be reset to home position. Other usability is usage of two manipulators in a modeling program (orbiting around the model, walking on the model) and changing between them while we want to preserve the position of a camera in the change. Games may benefit from it as well when we change from user-defined helicopter manipulator to soldier manipulator because the user escaped the helicopter. The camera will change manipulator but the position is expected to be kept in the transition (provided that user makes the state transition between the two manipulators himself).
"
From Robert Osfield, I didn't merge the change of parameter type of IntersectKdTree::intersect() as the internal maths is all done in Vec3s. Keeping Vec3 here hasn't effected the test results.
destruction of RequestQueue to remove any pointers held in DatabaseRequest attached to the scene graph, and to
prevent their subsequent use in cases where the scene graph is attached to a new DatabasePager.
to the osgDB::Registry. Added a osgDB::Registry::getObjectWrapperManager() for access of this object wrapper manager. This
change centralises the singleton management in osgDB.
Merged the osgDB::GlobalLookUpTable functionality into ObjectWrapperManger to keep down the number of singletons in use.
From Robert Osfield, refactor of Wang Rui's original osg2 into 3 parts - parts placed into osgDB, the ReaderWriter placed into src/osg/Plugin/osg and wrappers into src/osgWrappers/serializers/osg
osg::Texture1D classes, for the reason of implementing the I/O
serialization feature. In the Sequence header, I've added some more
convenient functions: setTimeList/getTimeList,
setLoopMode/getLoopMode, setBegin/getBegin, setEnd/getEnd,
setSpeed/getSpeed and setNumRepeats/getNumRepeats.
In the Texture1D header, fixed:
inline void setTextureWidth(int width) const ...
to:
inline void setTextureWidth(int width) ..."
Notes from Robert Osfield, have gone a little further with these changes and have removed some of the original get methods that were out of step with the way the rest of the OSG manages the set/get property pairs.
1. The node type will be set to ATOM on read of <tag prop="..." ... /> type tags.
2. GROUP and NODE are now written using the same code (and not just duplicated code). Also NODE will not be written as an ATOM if it has no children or contents, so you need to set the type to ATOM if you want the <tag ... /> style.
3. You had put the write of "/>" for ATOM after the "return true", so it had no effect... Moved to before the return.
4. ATOM did not write its properties correctly, fixed.
5. As an added bonus, I made the write() method indent the output so it's more readable. It brings a small public interface change but the indent argument has a default value so client code doesn't need to change (if there even is any).
6. Another added bonus, I've simplified the write() method a bit by factoring out the write for children and properties into protected methods."
1) Add getShadowComparison() accessor function to osg::Texture class
2) Modify ReaderWriterTiff::writeTifStream() and _readColor() (in Image.cpp) to handle pixelFormat==GL_DEPTH_COMPONENT as if it were GL_LUMINANCE
3) Modify the Texture classes of the ive and osg plug-ins so that they save/load the following Texture members: _use_shadow_comparison, _shadow_compare_func and _shadow_texture_mode
"
glActiveTexture on every State::apply after more than one texunits have been
used.
This is against 2.9.6 (I think SVN head is the same)
Quick Synopsis:
New functions:
State::applyModeOnTexUnit
State::applyAttributeOnTexUnit
State::applyModeMapOnTexUnit
State::applyAttributeMapOnTexUnit
State::applyModeListOnTexUnit
State::applyAttributeListOnTexUnit
All copies of the normal versions, but they also set the active tex unit if
absolutely necessary (i.e. only if they call something OpenGL).
State::apply (*2)
State::applyTextureAttribute
Changed to call the above functions and no longer call setActiveTextureUnit
themselves.
State::setActiveTextureUnit
Made inline, so the benefit of having applyModeOnTexUnit (etc) inline
is retained.
"
To enable the automatic attachment of the required update callback to call osg::Image::update(..) subclasses from osg::Image will
need to implement the osg::Image::requestUpdateCall() and return true, and implement the osg::Image::update(NodeVisitor*) method to recieve the update call during the update traversal.
Add check in RigTransformSoftware if bones are null
Indent TimelineAnimationManager
Add check for NaN in UpdateCallback.cpp
Fix TimelineAnimationManager clear target (a refactore of Timeline is require for futur)
Fix Computation of bounding box for RigGeometry
The texture in data/Images should be copied to osg-data. I created the texture myself with the help of an explosion generator, so no license issues there.
"
http://www.mail-archive.com/osg-users@lists.openscenegraph.org/msg33967.html
, interpolating through HSV space gives a rainbow color effect which
does not mimic the simple RGB color interpolation that OpenGL does.
It's overkill and causes unexpected visual artifacts. In the attached
files I've removed the conversion to HSV so that interpolation happens
in RGB space."
osg::GraphicsContext, in order to give good integration with the
application's GUI toolkit. This works really well.
However, I need to share OpenGL texture resources with the standard
osgViewer GraphicsContext implementations, in particular the
PixelBuffers. This is essential for my application to conserve graphics
memory on low-end hardware. Currently the standard osg implementations
will not share resources with another derived osg::GraphicsContext,
other than the pre-defined osgViewer classes e.g. PixelBufferX11 is
hardcoded to only share resources with GraphicsWindowX11 and
PixelBufferX11 objects, and no other osg::GraphicsContext object.
To address this in the cleanest way I could think of, I have moved the
OpenGL handle variables for each platform into a small utility class,
e.g. GraphicsHandleX11 for unix. Then GraphicsWindowX11, PixelBufferX11
and any other derived osg::GraphicsContext class can inherit from
GraphicsHandleX11 to share OpenGL resources.
I have updated the X11, Win32 and Carbon implementations to use this.
The changes are minor. I haven't touched the Cocoa implmentation as
I'm not familiar with it at all and couldn't test it - it will work
unchanged.
Without this I had some horrible hacks in my application, this greatly
simplifies things for me. It also simplifies the osgViewer
implementations slightly. Perhaps it may help with other users'
desires to share resources with external graphics contexts, as was
discussed on the user list recently."
Notes from Robert Osfield, adapted Colin's submission to work with the new EGL related changes.
filenames starting with a dash "-" character from the (std::vector<std::string>&) version
of osgDB::readNodeFiles. Handling of argument strings is properly implemented in the
osgDB::readNodeFiles(osg::ArgumentParser& arguments,const Options* options)
variant, which most code uses. The (std::vector<std::string>&) version is only called by
the osgconv utility, which does its own argument handling and stripping prior to calling
readNodeFiles().
Also, documented this behaviour in the header comments.
I believe this code removal is a meritful change because leavign the code in causes an
unexpected and undocumented behaviour (ignoring any filename starting with a dash) that
could bite users in the future. This behaviour is not needed for existing functionality
because existing code uses other APIs to handle dash-prefixed arguments anyway.
"
only create 376, then the program would hang.
376 * 8MB stack per thread = 3008 MB
The stack size allocated per thread blew the process address stack.
To get more threads you have to specify a smaller per thread stack,
but while the Thread::start says it will limit the stack size to the
smallest allowable stack size, it won't let it be smaller than the
default. I included the limits.h header to use PTHREAD_STACK_MIN as
the minimum stack size.
As for the deadlock, if the pthread_create failed, the new thread
doesn't exist and doesn't call threadStartedBlock.release(), so the
existing thread deadlocks on threadStartedBlock.block(). Only block
if the thread was started."
I've needed to run a recorded simulation offscreen and save it to a sequence of images, and the ScreenCaptureHandler seemed to be the simplest way to do that, and with this change it's possible.
Another change: I've also added the ability to specify continuous capture of all frames, or a certain number of frames. ScreenCaptureHandler now has a setFramesToCapture(int) method. The argument will be interpreted as:
0 : don't capture
<0 : capture continuously
>0 : capture that number of frames then stop
I also added startCapture() and stopCapture() methods so that user code can start capturing (either continuously or the given number of frames) at a given point in their program. setFramesToCapture() won't start capturing, you have to call startCapture() afterwards. The handler also now has another key to toggle continuous capture (defaults to 'C').
Note that continuous capture will of course only work if the CaptureOperation writes to different files (for example, a WriteToFile with SEQUENTIAL_NUMBER mode) or does something different each time... Otherwise it will just overwrite of course. :-)
I've also taken the chance to refactor the addCallbackToViewer() method a bit too, since finding the right camera is needed in two places now.
I've tested all cases (I think). If you want to try, in osgviewer.cpp and replace the line
// add the screen capture handler
viewer.addEventHandler(new osgViewer::ScreenCaptureHandler);
with
// add the screen capture handler
osgViewer::ScreenCaptureHandler* captureHandler = new
osgViewer::ScreenCaptureHandler(
new osgViewer::ScreenCaptureHandler::WriteToFile(
"screenshot", "jpg",
osgViewer::ScreenCaptureHandler::WriteToFile::SEQUENTIAL_NUMBER),
-1);
viewer.addEventHandler(captureHandler);
captureHandler->startCapture();
And vary the "-1" (put 0, 10, 50) and then use the 'c' and 'C' keys and see how it reacts.
"
DisplaySettings now define COLOR and DEPTH as defaults for implicit buffers. Consequently Camera by default uses the same defaults through USE_DISPLAY_SETTINGS_MASK. However, particular Camera mask can be easily overriden through Camera::setImplicitBufferAttachmentMask method. I hope, that in this way we can have global control over implicit buffer defaults, and we can still retain fine grained control at Camera level.
I have also replaced original unsigned ints used to store masks to signed ints because complier resolves enums as signed integer (I got a number of warnings with unsigned int)."
Most notable the __hpux define stuff. The __hpux__ variant seems to be not
defined which resulted in a compile error at this time. Consequently I have
replaced all occurances of __hpux__ with __hpux. And huge surprise: now osg
plugins are found and loaded correctly ...
The next notable one is the MSVC_IDE fix which makes the nmake Makefiles cmake
generator target behave like the ide one. Showed up because I started to do
scripted builds with nmake instead of devenv...
The rest is the usual bunch of stuff that just happens during normal
coding ..."
Fixed to osg::Texture for GLES support.
Added automatic GLenum mode mappings in osg::PrimitiveSet to provide a fallback for non support glDrawArray/glDrawElement modes.
Added finer gained error checking during StateSet::compile().
Moved the handling of DisplaySettings into Traits constructor.
Added support for s/getGLContextVersion(), s/getGLContextFlags() and s/getGLContextProfileMask() to osg::DisplaySettings.
Added command line and env var support for setting the GLContextVersion, GLContextFlags and GLContextProfileMask to osg::DisplaySettings.
Removed EXT postfix of FrameBufferObject functions, and added support for checking non EXT versions frame buffer object GL functions.
Introduced usage of OSG_GL*_FEATURES to avoid some #if #else #endif code blocks.
Using a submissions from Paul Martz as a guide added perliminary GL3 support to a range of OSG classes
* Refactore of RigGeometry to support hardware skinning
* Refactore of Timeline to split Action in differents files
* Add example how to use hardware skinning
* Change ref_ptr to observer_ptr to avoid cross reference and leak in Skinning
* Set invalidate to true to re run the check visitor in Skeleton
* Shallow copy Sampler in channel copy constructor
* Add accessor in VertexInfluence
* Remove dead code in Timeline.cpp
* Dont force linking in Bone::UpdateBone, the decision is done by the user or the manager
* Add offset in timeline stats to display each manager on the screen
* Add a flag in animation manager base to enable or not automatic link when modifying the manager
Added support for automatic aliasing of vertex, normal, color etc. arrays to Vertex Attribute equivelants.
Added new osg::GLBeginEndAdapter class for runtime conversion from glBegin/glEnd codes to vertex arrray equivelants.
Added automatic shader source conversion from gl_ to osg_ builtins.
of an osgWidget::Label with an osgText::String. I had to do this on a
project I'm working on, because I needed UTF-8 strings on my labels,
and using setLabel with std::string was not working.
"
It adds new PrimitiveSet constants for the specific geometry shader primitive types :
- LINES_ADJACENCY
- LINE_STRIP_ADJACENCY
- TRIANGLES_ADJACENCY
- TRIANGLE_STRIP_ADJACENCY
It also adds some missing features to the glsl reader plug'in.
"
The Texture Pool can be enabled by setting the env var OSG_TEXTURE_POOL_SIZE=size_in_bytes.
Note, setting a size of 1 will result in the TexturePool allocating the minimum number of
textures it can without having to reuse TextureObjects from within the same frame.
Finally, I have fixed TemplateTarget<osg::Quat>::lerp() as it was giving incorrect results when interpolating between some small rotations.
From Cedric Pinson, i renamed the method in channel to be more general. Adjusted the CubicBezier key constructor to use a single value as input.
Update Timeline.cpp to add current layer to the ActionVisitor, use correctly the priority
Add accessors in Action.cpp to retrieve protected data
Split files and rename them to classname
Change de default color of UpdateMaterial to FFOOFF to detect unset value
Add accessors in LinkVisitor instead of accessing data directly
Update osganimationtimeline example to fit the api callback
- Animations with equal priority are now weighted correctly relative to each other
- (minor) Channels no longer store their weight as the only time it's used is in update() when Animation can pass in the weight directly
From Cedric Pinson,
- I adjusted the quaternion blending to keep the commutativy property
osg::Animation::TemplateStepInterpolator::getValue the code tries to return
the result rather than assigning it to the result parameter reference.
The following patch fixes this."
Note from Robert Osfield, I've temporarily re-enabled the old focing of of color and depth attachment to avoid regressions on some OpenGL driver. We'll revist this once
we have a mechanism for controlling this override at runtime.
#define FORCE_COLOR_ATTACHMENT 1
#define FORCE_DEPTH_ATTACHMENT 1
dragger="box" or dragger="trackball"
and
technique="light" or technique="isosurface" or technique="iso" or technique="mip"
and
tf="transferfunctionfile.tf"
i.e.
<volume dragger="box">CardiacCT</volume>
<volume tf="colour.tf">CardiacCT</volume>
<volume technique="isosurface">CardiacCT</volume>
behind osgText::Text. I made it so the box would get drawn using
whichever BackdropImplementation was selected. However, I did not
implement STENCIL_BUFFER. In that case it defaults to drawing the
bounding box using POLYGON_OFFSET instead.
Also made it so the BOUNDINGBOX and FILLEDBOUNDINGBOX are drawn with a
settable color and margin size.
While I was at it I tightened up the values applied with DEPTH_RANGE
and POLYGON_OFFSET, not just for drawing the bounding box but also for
drawing backdrop text (these values must be coupled since the bounding
box has to be drawn deeper in Z than the backdrop text). The values
in use before seemed like overkill and I was seeing some z-clipping
with my background scenery in the case of DEPTH_RANGE. If there was a
good reason for the large values please let me know...."
GraphicsWindowCocoa-implementation, which enhances multithreaded
stability, it ensures that modifications to the size of an openglcontext
is done only from one thread.
"
Selection is now just a typedef of osg::MatrixTransform, and is deprecated
CommandManager is shell class that just sets values directly on Dragger, and is deprecated
Dragger now has list of DraggerCallback that takes over the roll of tracking changes to the Dragger, and
allows users to track the dragger in any way they wish.
Dragger now has a convinience method making MatrixTransforms track a dragger.
Selection and CommandManager are no longer required for use of osgManipulator and are kept around for backwards compatibility.
dependent on the complexity of the geometry. For complex scenes this
meant that it looked like you were "throwing" the display into molasses.
For simple geometry things get over-excited once thrown.
The fix is to factor in the frame rendering time to the caluclated
motion. I've implemented this for rotation and panning.
Now when things are thrown they maintain a rate very close to what was
happening when the mouse button was released."
Enclosed is include/osgParticle/Particle. I removed the const from the
return type of getSTexCoord. I also changed the name on the next
function to getTTexCoord so it is consistent with getSTexCoord. If you
prefer to change getSTexCoord to getSCoord you will need to change it in
ConnectedParticleSystem.cpp."
- osg::Texture sets GL_MAX_TEXTURE_LEVEL if image uses fewer mipmaps than
number from computeNumberOfMipmaps (and it works!)
- DDS fix to read only available mipmaps
- DDS fixes to read / save 3D textures with mipmaps ( packing == 1 is
required)
- Few cosmetic DDS modifications and comments to make code cleaner (I hope)
Added _isTextureMaxLevelSupported variable to texture extensions. It
could be removed if OSG requires OpenGL version 1.2 by default.
Added simple ComputeImageSizeInBytes function in DDSReaderWrites. In
my opinion it would be better if similar static method was defined for
Image. Then it could be used not only in DDS but other modules as well (I
noticed that Texture/Texture2D do similar computations).
Also attached is an example test.osg model with DDS without last mipmaps to
demonstrate the problem. When loaded into Viewer with current code and moved
far away, so that cube occupies 4 pixels, cube becomes red due to the issue
I described in earlier post. When you patch DDS reader writer with attched
code but no osg::Texture yet, cube becomes blank (at least on my
Windows/NVidia) When you also merge osg::Texture patch cube will look right
and mipmaps will be correct."
database options like recently added to PagedLOD.
Also there is a change to the traverse method:
The previous ProxyNode checks the VisitorType to be a CULL_VISITOR and the
presence of a request handler to submit a database request.
In contrast to that PagedLOD uses the request handler if it is there - even if
the visitor type is not a cull visitor.
The change removes the cull visitor test from the ProxyNode so that it behaves
like the PagedLOD.
I believe that the presence of a request handler in a visitor might be
sufficient to trigger the requests as this is done in the PagedLOD anyway.
Based on rev 10332."
First Submission email from Gustav:
"This submission adds a --cache option to osgconv and osgviewer that enables setObjectCacheHint(osgDB::Options::CACHE_ALL); It greatly reduces memory usage when a .osg file has lots of external references with ProxyNode:s that points to the same file.
Options are also added to the osg plugin. The code was already mostly implemented but there was no way to change the options.
includeExternalReferences
writeExternalReferenceFiles
A counter is added to keep track if an external file has already been written down to avoid writing the same file over and over again. If it has already been written once then it is not written again.
The counter is added to the Output class in osgDB.
"
Second Submission email from Gustav:
"This is a continuation to my previous submission.
I noticed that the same problem that I fixed in ProxyNode.cpp for the osg plugin (external files being written over and over again) also existed in the ive plugin. I attached a submission where the ive plugin remembers which external files that have already been written and do not write them again."
Changes to the above done by Robert Osfield,
changed command line parameter to --enable-object-cache
changed set/get methods in osgDB::Output and ive/DataOutputStream.cpp to be s/getExternalFileWritten(const std::string&)
cleaned up set up of osgDB::Options.
of these methods in src/osgViewer/Renderer.cpp to make sure that the draw thread keeps references to all in scene graph Cameras
that are being used by the drawing threads, to keep the Camera's alive even when the main thread removes these Cameras from the scene graph.
This makes it possible to redefine the viewing direction of 'home' in the other manipulator - so home in a GIS app could be a plan view.
Since _homeUp is set to (0,0,1) and no current code changes it there shouldn't be any difference for current users."
Two implementations of NotifyHandler are currently available:
- StandardNotifyHandler, calls fputs(message, stderr) for severity <= WARN and fputs(message, stdout) for severity > WARN
- WinDebugNotifyHandler, windows users can redirect notifications to windows debug output, notifications can be viewed in output window of the debugger i.e. MSVC or DebugView (http://technet.microsoft.com/en-us/sysinternals/bb896647.aspx) (see screenshot).
I have seen on osg-users that some people do std::cerr.rdbuf(otherStream.rdbuf()) to redirect notifications. This trick will no longer work since osg::notify() returns internal osg::NotifyStream not std::cout or std::cerr. You can use osg::notify().rdbuf(otherStream.rdbuf()) to do this instead.
Additionally I've made some minor fixes:
- Minor imrovements to osg::notify documentation
- NullStream could crash by deleting stream buffer other than default NullStreamBuffer in the destructor i.e. after osg::notify(osg::DEBUG_FP).rdbuf(otherStream.rdbuf())"
The changes are more or less just beautifications
(when looked at them from the C++ view), but make
wrapping OSG with SWIG easier.
I have tested the changes with both 2.8.1-rc4 and the
current head and would appreciate to incorporate the
changes in both branches.
Here is a description of the changes:
osg/BoundingSphere:
Use the following typedef (like used in BoundingBox)
typedef typename VT::value_type value_type;
instead of
typedef typename vec_type::value_type value_type;
SWIG reports errors on the latter construct.
Also makes it consistent with BoundingBox.
osg/Vec4ub:
Consistent use of "value_type" throughout the file.
osg/Vec?b:
Consistent use of "value_type" throughout the files.
Also changed
typedef char value_type;
to
typedef signed char value_type;
In the case of a simple "char", SWIG assumes a string.
Using "signed char" instead of "char" does not change
the behaviour of the class.
"
implementation of GraoicsWindowCocoa:
Enhancements/Bugfixes:
+ now it's possible to integrate osgViewer better into existing
cocoa-applications:
* create one or more NSOpenGLView(s) and add these to your window(s)
* create one or more NSWindows
* disable the integrated event-polling of osgViewer, and let the work be
done by Cocoa / NSApplicationRun. You'll have to run the osgViewer's
runloop in a separate thread
+ missing menu-event-handling implemented
+ added NSAutoReleasePools where necessary, this fixes some memory-leaks
+ fixed some crashes and thread-issues"
Introduced a new callback osgDB::FindFileCallback that overrides the default behavior of findDataFile/findLibraryFile.
Introduced support for assigning ReaderWriter::Options directory to PagedLOD.
Introduced new osgDB::FileLocationCallback for assistancing the DatabasePager to know when a file is hosted on a local or remote file system.
Introduced a new FindFileCallback to Registry to compliement the existing ReadFileCallback and WriteFileCallback.
Added support for assign Find, Read and WriteFileCallbacks to osdDB::Options to enable plugins/applications to override the callbacks just for that
read/write call and any nested file operations
Original email from Frederic at start of thread:
"he patch attached, made from r10068, fix two things, in other of importance :
- the selected cursor is never shown ( second change in file ). Only the left arrow is always displayed.
- remove the arbitrary ( in my sense ) limitation that the user cannot choose a cursor with the same shape that one used when resizing the window. This limitation doesn't exist for X11, and we have a diverging behaviour there ( first change in file ). Flightgear use the LeftRightCursor in look around mode."
Follow up email from Frederic (with changes that finally made it into this check in:
"I've just tested Mark's suggestion and it works perfectly, even when the
cursor goes to the border then come back inside the window.
But his patch doesn't seem to be based on the last revision of the
files, or at least not on the trunk, and there are more changes than
expected in them, including some loss from the previous patches.
The patch attached is based on r10068 of
src/osgViewer/GraphicsWindowWin32.cpp and r10067 of
include/osgViewer/api/Win32/GraphicsWindowWin32"
Converted Present3D across from using libxml2 to using the new osgDB::XmlNode/XmlNode::Input classes from Xml Parsing.
This changes removes the dependency on libxml2, and allows the present3D application and p3d to work on all platforms.
http://www.mail-archive.com/osg-users@lists.openscenegraph.org/msg23734.html
The change is source compatible with current osg code and will not affect current users, it simply adds an additional parameter to the GraphicsWindowWin32::WindowData struct constructor and defaults to the current behavior.
Attached are the files "include/osgViewer/api/Win32/GraphicsWindowWin32" and "src/osgViewer/GraphicsWindowWin32.cpp" with my changes, based on svn revision 10045. In addition, I have provided an svn patch file with the same changes for your convenience.
I have discussed the matter with my supervisor, and agreed that my company makes no copyright claim over this extremely trivial change (or to put it another way, we assign copyright to the open scene graph community.)"
TrackballManipulator. The purpose of this is to disable throwing when
you release the mouse button while moving the mouse. The default
settings is true (ie, allow throw). The two source files are attached.
"
(http://www.mail-archive.com/osg-users@lists.openscenegraph.org/msg23098.html)
Background: when you access a file over HTTP, you cannot rely on a file extension being present; instead the file's mime-type is conveyed in the HTTP Content-Type response header. This facility adds a mime-type-to-extension map to the registry to handle this.
There are two new osgDB::Registry functions which are pretty self-explanatory:
void addMimeTypeExtensionMapping( mime-type, extension )
ReaderWriter* getReaderWriterForMimeType( mime-type )
I also added the file osgDB/MimeTypes.cpp which houses a hard-coded list of built-in types. I took the list from here (http://www.webmaster-toolkit.com/mime-types.shtml) and then pared it down to include mostly image and video types, editing them to map to existing plugins where possible.
In addition, I updated the CURL plugin to a) install a set of built-in mime-type mappings, and b) use them to look up an extension in the event that the target filename does not have an extension.
Here is a test case. This URL pulls down a JPEG (without a file extension):
osgviewer --image "http://us.maps3.yimg.com/aerial.maps.yimg.com/ximg?v=1.8&s=256&t=a&r=1&x=0&y=0&z=2"
"
