4c5a1885d2
algorithm consisting of two consequent phases :
- first phase is a GLSL shader performing object culling and LOD picking ( a culling shader ).
Every culled object is represented as GL_POINT in the input osg::Geometry.
The output of the culling shader is a set of object LODs that need to be rendered.
The output is stored in texture buffer objects. No pixel is drawn to the screen
because GL_RASTERIZER_DISCARD mode is used.
- second phase draws osg::Geometry containing merged LODs using glDrawArraysIndirect()
function. Information about quantity of instances to render, its positions and other
parameters is sourced from texture buffer objects filled in the first phase.
The example uses various OpenGL 4.2 features such as texture buffer objects,
atomic counters, image units and functions defined in GL_ARB_shader_image_load_store
extension to achieve its goal and thus will not work on graphic cards with older OpenGL
versions.
The example was tested on Linux and Windows with NVidia 570 and 580 cards.
The tests on AMD cards were not conducted ( due to lack of it ).
The tests were performed using OSG revision 14088.
The main advantages of this rendering method :
- instanced rendering capable of drawing thousands of different objects with
almost no CPU intervention ( cull and draw times are close to 0 ms ).
- input objects may be sourced from any OSG graph ( for example - information about
object points may be stored in a PagedLOD graph. This way we may cover the whole
countries with trees, buildings and other objects ).
Furthermore if we create osgDB plugins that generate data on the fly, we may
generate information for every grass blade for that country.
- every object may have its own parameters and thus may be distinct from other objects
of the same type.
- relatively low memory footprint ( single object information is stored in a few
vertex attributes ).
- no GPU->CPU roundtrip typical for such methods ( method uses atomic counters
and glDrawArraysIndirect() function instead of OpenGL queries. This way
information about quantity of rendered objects never goes back to CPU.
The typical GPU->CPU roundtrip cost is about 2 ms ).
- this example also shows how to render dynamic objects ( objects that may change
its position ) with moving parts ( like car wheels or airplane propellers ) .
The obvious extension to that dynamic method would be the animated crowd rendering.
- rendered objects may be easily replaced ( there is no need to process the whole
OSG graphs, because these graphs store only positional information ).
The main disadvantages of a method :
- the maximum quantity of objects to render must be known beforehand
( because texture buffer objects holding data between phases have constant size ).
- OSG statistics are flawed ( they don't know anymore how many objects are drawn ).
- osgUtil::Intersection does not work
Example application may be used to make some performance tests, so below you
will find some extended parameter description :
--skip-dynamic - skip rendering of dynamic objects if you only want to
observe static object statistics
--skip-static - the same for static objects
--dynamic-area-size - size of the area for dynamic rendering. Default = 1000 meters
( square 1000m x 1000m ). Along with density defines
how many dynamic objects is there in the example.
--static-area-size - the same for static objects. Default = 2000 meters
( square 2000m x 2000m ).
Example application defines some parameters (density, LOD ranges, object's triangle count).
You may manipulate its values using below described modifiers:
--density-modifier - density modifier in percent. Default = 100%.
Density ( along with LOD ranges ) defines maximum
quantity of rendered objects. registerType() function
accepts maximum density ( in objects per square kilometer )
as its parameter.
--lod-modifier - defines the LOD ranges. Default = 100%.
--triangle-modifier - defines the number of triangles in finally rendered objects.
Default = 100 %.
--instances-per-cell - for static rendering the application builds OSG graph using
InstanceCell class ( this class is a modified version of Cell class
from osgforest example - it builds simple quadtree from a list
of static instances ). This parameter defines maximum number
of instances in a single osg::Group in quadtree.
If, for example, you modify it to value=100, you will see
really big cull time in OSG statistics ( because resulting
tree generated by InstanceCell will be very deep ).
Default value = 4096 .
--export-objects - write object geometries and quadtree of instances to osgt files
for later analysis.
--use-multi-draw - use glMultiDrawArraysIndirect() instead of glDrawArraysIndirect() in a
draw shader. Thanks to this we may render all ( different ) objects
using only one draw call. Requires OpenGL version 4.3 and some more
work from me, because now it does not work ( probably I implemented
it wrong, or Windows NVidia driver has errors, because it hangs
the apllication at the moment ).
This application is inspired by Daniel Rákos work : "GPU based dynamic geometry LOD" that
may be found under this address : http://rastergrid.com/blog/2010/10/gpu-based-dynamic-geometry-lod/
There are however some differences :
- Daniel Rákos uses GL queries to count objects to render, while this example
uses atomic counters ( no GPU->CPU roundtrip )
- this example does not use transform feedback buffers to store intermediate data
( it uses texture buffer objects instead ).
- I use only the vertex shader to cull objects, whereas Daniel Rákos uses vertex shader
and geometry shader ( because only geometry shader can send more than one primitive
to transform feedback buffers ).
- objects in the example are drawn using glDrawArraysIndirect() function,
instead of glDrawElementsInstanced().
Finally there are some things to consider/discuss :
- the whole algorithm exploits nice OpenGL feature that any GL buffer
may be bound as any type of buffer ( in our example a buffer is once bound
as a texture buffer object, and later is bound as GL_DRAW_INDIRECT_BUFFER ).
osg::TextureBuffer class has one handy method to do that trick ( bindBufferAs() ),
and new primitive sets use osg::TextureBuffer as input.
For now I added new primitive sets to example ( DrawArraysIndirect and
MultiDrawArraysIndirect defined in examples/osggpucull/DrawIndirectPrimitiveSet.h ),
but if Robert will accept its current implementations ( I mean - primitive
sets that have osg::TextureBuffer in constructor ), I may add it to
osg/include/PrimitiveSet header.
- I used BufferTemplate class writen and published by Aurelien in submission forum
some time ago. For some reason this class never got into osg/include, but is
really needed during creation of UBOs, TBOs, and possibly SSBOs in the future.
I added std::vector specialization to that template class.
- I needed to create similar osg::Geometries with variable number of vertices
( to create different LODs in my example ). For this reason I've written
some code allowing me to create osg::Geometries from osg::Shape descendants.
This code may be found in ShapeToGeometry.* files. Examples of use are in
osggpucull.cpp . The question is : should this code stay in example, or should
it be moved to osgUtil ?
- this remark is important for NVidia cards on Linux and Windows : if
you have "Sync to VBlank" turned ON in nvidia-settings and you want to see
real GPU times in OSG statistics window, you must set the power management
settings to "Prefer maximum performance", because when "Adaptive mode" is used,
the graphic card's clock may be slowed down by the driver during program execution
( On Linux when OpenGL application starts in adaptive mode, clock should work
as fast as possible, but after one minute of program execution, the clock slows down ).
This happens when GPU time in OSG statistics window is shorter than 3 ms.
"
git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/trunk@14531 16af8721-9629-0410-8352-f15c8da7e697
Welcome to the OpenSceneGraph (OSG).
For up-to-date information on the project, in-depth details on how to
compile and run libraries and examples, see the documentation on the
OpenSceneGraph website:
http://www.openscenegraph.org/index.php/documentation
For support subscribe to our public mailing list or forum, details at:
http://www.openscenegraph.org/index.php/support
For the impatient, we've included quick build instructions below, these
are are broken down is three parts:
1) General notes on building the OpenSceneGraph
2) OSX release notes
3) iOS release notes
If details below are not sufficient then head over to the openscenegraph.org
to the Documentation/GettingStarted and Documentation/PlatformSpecifics sections for
more indepth instructions.
Robert Osfield.
Project Lead.
24th July 2013.
--
Section 1. How to build the OpenSceneGraph
==========================================
The OpenSceneGraph uses the CMake build system to generate a
platform-specific build environment. CMake reads the CMakeLists.txt
files that you'll find throughout the OpenSceneGraph directories,
checks for installed dependenciesand then generates the appropriate
build system.
If you don't already have CMake installed on your system you can grab
it from http://www.cmake.org, use version 2.4.6 or later. Details on the
OpenSceneGraph's CMake build can be found at:
http://www.openscenegraph.org/projects/osg/wiki/Build/CMake
Under unices (i.e. Linux, IRIX, Solaris, Free-BSD, HP-Ux, AIX, OSX)
use the cmake or ccmake command-line utils. Note that cmake . defaults
to building Release to ensure that you get the best performance from
your final libraries/applications.
cd OpenSceneGraph
cmake .
make
sudo make install
Alternatively, you can create an out-of-source build directory and run
cmake or ccmake from there. The advantage to this approach is that the
temporary files created by CMake won't clutter the OpenSceneGraph
source directory, and also makes it possible to have multiple
independent build targets by creating multiple build directories. In a
directory alongside the OpenSceneGraph use:
mkdir build
cd build
cmake ../OpenSceneGraph
make
sudo make install
Under Windows use the GUI tool CMakeSetup to build your VisualStudio
files. The following page on our wiki dedicated to the CMake build
system should help guide you through the process:
http://www.openscenegraph.org/index.php/documentation/platform-specifics/windows
Under OSX you can either use the CMake build system above, or use the
Xcode projects that you will find in the OpenSceneGraph/Xcode
directory. See release notes on OSX CMake build below.
For further details on compilation, installation and platform-specific
information read "Getting Started" guide:
http://www.openscenegraph.org/index.php/documentation/10-getting-started
Section 2. Release notes on OSX build, by Eric Sokolowsky, August 5, 2008
=========================================================================
There are several ways to compile OpenSceneGraph under OSX. The
recommended way is to use CMake 2.6 to generate Xcode projects, then use
Xcode to build the library. The default project will be able to build
Debug or Release libraries, examples, and sample applications. Here are
some key settings to consider when using CMake:
BUILD_OSG_EXAMPLES - By default this is turned off. Turn this setting on
to compile many great example programs.
CMAKE_OSX_ARCHITECTURES - Xcode can create applications, executables,
libraries, and frameworks that can be run on more than one architecture.
Use this setting to indicate the architectures on which to build OSG.
Possibilities include ppc, ppc64, i386, and x86_64. Building OSG using
either of the 64-bit options (ppc64 and x86_64) has its own caveats
below.
OSG_BUILD_APPLICATION_BUNDLES - Normally only executable binaries are
created for the examples and sample applications. Turn this option on if
you want to create real OSX .app bundles. There are caveats to creating
.app bundles, see below.
OSG_WINDOWING_SYSTEM - You have the choice to use Carbon or X11 when
building applications on OSX. Under Leopard and later, X11 applications,
when started, will automatically launch X11 when needed. However,
full-screen X11 applications will still show the menu bar at the top of
the screen. Since many parts of the Carbon user interface are not
64-bit, X11 is the only supported option for OSX applications compiled
for ppc64 or x86_64.
There is an Xcode directory in the base of the OSG software
distribution, but its future is limited, and will be discontinued once
the CMake project generator completely implements its functionality.
APPLICATION BUNDLES (.app bundles)
The example programs when built as application bundles only contain the
executable file. They do not contain the dependent libraries as would a
normal bundle, so they are not generally portable to other machines.
They also do not know where to find plugins. An environmental variable
OSG_LIBRARY_PATH may be set to point to the location where the plugin
.so files are located. OSG_FILE_PATH may be set to point to the location
where data files are located. Setting OSG_FILE_PATH to the
OpenSceneGraph-Data directory is very useful when testing OSG by running
the example programs.
Many of the example programs use command-line arguments. When
double-clicking on an application (or using the equivalent "open"
command on the command line) only those examples and applications that
do not require command-line arguments will successfully run. The
executable file within the .app bundle can be run from the command-line
if command-line arguments are needed.
64-BIT APPLICATION SUPPORT
OpenSceneGraph will not compile successfully when OSG_WINDOWING_SYSTEM is
Carbon and either x86_64 or ppc64 is selected under CMAKE_OSX_ARCHITECTURES,
as Carbon is a 32bit only API. A version of the osgviewer library written in
Cocoa is needed. However, OSG may be compiled under 64-bits if the X11
windowing system is selected. However, Two parts of the OSG default
distribution will not work with 64-bit X11: the osgviewerWX example
program and the osgdb_qt (Quicktime) plugin. These must be removed from
the Xcode project after Cmake generates it in order to compile with
64-bit architectures. The lack of the latter means that images such as
jpeg, tiff, png, and gif will not work, nor will animations dependent on
Quicktime. A new ImageIO-based plugin is being developed to handle the
still images, and a QTKit plugin will need to be developed to handle
animations.
Section 3. Release notes on iOS build, by Thomas Hoghart
=========================================================
* Run CMake with either OSG_BUILD_PLATFORM_IPHONE or OSG_BUILD_PLATFORM_IPHONE_SIMULATOR set:
$ mkdir build-iOS ; cd build-iOS
$ ccmake -DOSG_BUILD_PLATFORM_IPHONE_SIMULATOR=YES -G Xcode ..
* Check that CMAKE_OSX_ARCHITECTURE is i386 for the simulator or armv6;armv7 for the device
* Disable DYNAMIC_OPENSCENEGRAPH, DYNAMIC_OPENTHREADS
This will give us the static build we need for iPhone.
* Disable OSG_GL1_AVAILABLE, OSG_GL2_AVAILABLE, OSG_GL3_AVAILABLE,
OSG_GL_DISPLAYLISTS_AVAILABLE, OSG_GL_VERTEX_FUNCS_AVAILABLE
* Enable OSG_GLES1_AVAILABLE *OR* OSG_GLES2_AVAILABLE
* Ensure OSG_WINDOWING_SYSTEM is set to IOS
* Change FREETYPE include and library paths to an iPhone version
(OpenFrameworks has one bundled with its distribution)
* Ensure that CMake_OSX_SYSROOT points to your iOS SDK.
* Generate the Xcode project
* Open the Xcode project
$ open OpenSceneGraph.xcodeproj
* Under Sources -> osgDB, select FileUtils.cpp and open the 'Get Info' panel, change File Type
to source.cpp.objcpp
Here's an example for the command-line:
$ cmake -G Xcode \
-D OSG_BUILD_PLATFORM_IPHONE:BOOL=ON \
-D CMAKE_CXX_FLAGS:STRING="-ftree-vectorize -fvisibility-inlines-hidden -mno-thumb -arch armv6 -pipe -no-cpp-precomp -miphoneos-version-min=3.1 -mno-thumb" \
-D BUILD_OSG_APPLICATIONS:BOOL=OFF \
-D OSG_BUILD_FRAMEWORKS:BOOL=OFF \
-D OSG_WINDOWING_SYSTEM:STRING=IOS \
-D OSG_BUILD_PLATFORM_IPHONE:BOOL=ON \
-D CMAKE_OSX_ARCHITECTURES:STRING="armv6;armv7" \
-D CMAKE_OSX_SYSROOT:STRING=/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk \
-D OSG_GL1_AVAILABLE:BOOL=OFF \
-D OSG_GL2_AVAILABLE:BOOL=OFF \
-D OSG_GLES1_AVAILABLE:BOOL=ON \
-D OSG_GL_DISPLAYLISTS_AVAILABLE:BOOL=OFF \
-D OSG_GL_FIXED_FUNCTION_AVAILABLE:BOOL=ON \
-D OSG_GL_LIBRARY_STATIC:BOOL=OFF \
-D OSG_GL_MATRICES_AVAILABLE:BOOL=ON \
-D OSG_GL_VERTEX_ARRAY_FUNCS_AVAILABLE:BOOL=ON \
-D OSG_GL_VERTEX_FUNCS_AVAILABLE:BOOL=OFF \
-D DYNAMIC_OPENSCENEGRAPH:BOOL=OFF \
-D DYNAMIC_OPENTHREADS:BOOL=OFF .
Known issues:
* When Linking final app against ive plugin, you need to add -lz to
the 'Other linker flags' list.
* Apps and exes don't get created
* You can only select Simulator, or Device projects. In the XCode
project you will see both types but the sdk they link will
be the same.