osgSprites 

I.  Description

osgSprites is a complete node kit for diplaying large fields of sprite objects in OSG.  
The osgSprites library uses a geometry shader to render geometry aligned to screen 
space.  This has some drawbacks but these are worth the advantages, as it allows the 
rendering of one million trees with best of breed graphics gaming cards (2009).  


II.  Usage

There are three methods for using osgSprites.  Programatically, by generating a 
.sprites file, or by embedding the Sprites extension in a .osg file.  In any case, 
osgSprites build the tree forest with two sets of information:

    o A Texture Palette. 
    --------------------

    This texture palette is expected to have a palette of RGBA images of sprites.  Each image
    is referenced by index, starting from the lower left hand corner and counting right.  Each
    palette will have M rows and N columns, with 1 or more rows and 1 or more columns.


    o A list of Sprite Data

    The SpriteData consists a list of tuples each with the following pieces of information:

        a. width x height the sprite
        b. palette index
        c. position (X,Y,Z) of the sprite

This information is passed to the osgSprite library by one of the three methods of usage:

A.  Using osgSprites Programatically

Use the C++ osgSprites::Sprites interface.  Sprites derives from osg::Geode.
The following is an example C++ code example for using 

    /////////////////////////////////////////////////////////////////////////////////////////////////////////////
    static const unsigned int numTrees = 4000;
    
    osg::Geode *loadTrees()
    {
        // Open the pallete texture
        osg::ref_ptr<osg::Image> treePaletteImage = osgDB::readImageFile( "trees.png" );
        if( !treePaletteImage.valid() )
        {
            osg::notify( osg::WARN ) << "Can't open the tree palette image \"trees.png\"" << std::endl;
            return NULL;
        }
    
        // Make the Palette
        osg::ref_ptr<osgSprites::TexturePalette> texturePalette = 
                new osgSprites::TexturePalette( 1, 5, treePaletteImage.get() );
    
    
        // Invent some random tree positions 
        float area = sqrt((double)numTrees)/2.0;
        osgSprites::Sprites::SpriteDataList dataList;
        for( unsigned int i = 0; i < numTrees; i++ )
        {
            osgSprites::Sprites::SpriteData treeData;
    
            treeData.width  = 2.0f + ((float)(rand()%1000)/1000.0f) * 2.0f;
            treeData.height = 4.0f + ((float)(rand()%1000)/1000.0f) * 4.0f;
            treeData.paletteIndex = rand() % 5;
    
            treeData.position[0] = -(area*0.5) + ((float)(rand() % 10000)/10000.0f) * area;
            treeData.position[1] = -(area*0.5) + ((float)(rand() % 10000)/10000.0f) * area;
            treeData.position[2] = 0.0f;
    
            dataList.push_back( treeData );
        }
    
    
        // Create the Sprite Trees
        osg::ref_ptr<osgSprites::Sprites> trees = new osgSprites::Sprites( dataList );
        trees->setTexturePalette( texturePalette.get() );
    
        /// Hang 'em on a Geode
        osg::Geode *geode = new osg::Geode;
        geode->addDrawable( trees.get() );
    
        return geode;
    }
    /////////////////////////////////////////////////////////////////////////////////////////////////////////////

B. Using osgSprites in a .sprites file.

.trees files are XML files with three tags: <Sprite>, <TexturePalette> and <SpriteData>.  The following is an 
example .sprites file:

    <Sprites>
        <TexturePalette  imageFile="trees.png"  numRows="1"  numCols="5"    />
        <SpriteData  width="0.7704"  height="1.232"  paletteIndex="1">
            <Position  x="-29.255"  y="-26.621"  z="0"        />
    
        </SpriteData>
        <SpriteData  width="0.7704"  height="1.232"  paletteIndex="1">
            <Position  x="-30.053"  y="-45.737"  z="0"        />
    
        </SpriteData>
        <SpriteData  width="0.7704"  height="1.232"  paletteIndex="1">
            <Position  x="-49.823"  y="-26.711"  z="0"        />
    
        </SpriteData>
        <SpriteData  width="0.7704"  height="1.232"  paletteIndex="1">
            <Position  x="-22.484"  y="-32.792"  z="0"        />
    
        </SpriteData>
    
    </Sprites>


The .sprites file is parsed with the osgdb_sprites loader.


C. Extending the .osg file format

The following is an extended .osg file format supporting Sprites:

    Geode {
      name "example.trees"
      nodeMask 0xffffffff
      cullingActive TRUE
      num_drawables 1

      osgSprites::Sprites {
        UniqueID Sprites_0
        TexturePalette {
          fileName "trees.png"
          numRows  1
          numCols  5
        }
        Comment { 
          SpriteData records: 
          width height paletteIndex X Y Z
        }
        SpriteData { 
          0.7704  1.232  1  -2.9255 -2.6621 0
          0.7704  1.232  2  -1.0053 -2.5737 0
          0.7704  1.232  3  -1.9823 -2.6711 0
          0.7704  1.232  4  -2.2484 -1.2792 0
        }
      }

    }



III.  Building osgSprites

A. on Non-windows using DWMake

    1. In the root directory, type 'make'

       % make

    2. Install the libraries in their target location (by hand) as appropriate 

        % sudo cp lib/Linux64/libosgSprites.so@  /usr/local/lib64        
        % sudo cp lib/Linux64/osgdb_*.so /usr/local/lib64/osgPlugins-2.8.2/

    3. Optionally, if you need the development headers

        % sudo cp include/osgSprites/ /usr/local/include/

   
B. Using CMake

   If targeting Makefiles, PLEASE MAKE OUT OF SOURCE BUILDS as they will conflict with the
   GNUmakefiles of DWMake