Difference between revisions of "Io scene geo"

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Revision as of 20:11, 9 September 2013

Io_scene_geo is a basic example plugin. This wiki page is intended as a walkthrough of the code in order to help you better understand the SDK.

Functionality=

This plugin is a saver/loader that loads/saves VideoScape Geo files.

Code Walkthrough

Class Declarations

class CGEOParser : public CLxLineParser
{
    public:
        virtual bool		 lp_StripWhite ()	{ return true; }
        virtual bool		 lp_SkipBlank  ()	{ return true; }
};

Here we want to create a default line parser, so we have CGEOParser inherit from CLxLineParser and don't redeclare any functions. We do, however, declare two additional functions that will strip white space from the start and end of lines and skip blank lines.

class CGEOLoader : public CLxSceneLoader, public CGEOParser
{
    public:
        virtual CLxFileParser *	 sl_Parser    ()	{ return this; }

        virtual bool		 sl_Recognize ();
        virtual bool		 sl_ParseInit ();
        virtual bool		 sl_ParseDone ();
        virtual bool		 sl_Parse     (LxResult *);

        bool			 read_vrts;
        list<string>		 color_list;

        static LXtTagInfoDesc	 descInfo[];
};

Our loader, titled CGEOLoader, is a subclass of the CLxSceneLoader utility class, where we have overloaded the recognition and parsing methods. We also also want it to be its own parser, so we inherit from CGEOParser, and then return the parser through the sl_Parser() method.

class CGEOFormat : public CLxLineFormat
{
   public:
       virtual const char *	 lf_Separator  ()		{ return " "; }
};

We create CGEOFormat, which defines a line format. As a result we inherit from CLxLineFormat. The format we create is just a default line format with spaces delimiting elements on the same line.

class CGEOSaver : public CLxSceneSaver, public CGEOFormat
{
   public:
       virtual CLxFileFormat *	 ss_Format    ()	{ return this; }

       virtual void		 ss_Verify    ();
       virtual LxResult	 ss_Save      ();
       virtual void		 ss_Point     ();
       virtual void		 ss_Polygon   ();

       void			 GatherColors ();

       static LXtTagInfoDesc	 descInfo[];

       map<LXtPointID,unsigned> pnt_index;
       unsigned		 pnt_count;
       map<string,unsigned>	 matr_color;
       bool			 get_matr;
};

We want to create a utility that saves scenes, so we inherit from CLxSceneSaver. We also want the saver to have it's own format, so we inherit the format we created above.

Initialize

       void
initialize ()
{
       LXx_ADD_SERVER (Loader, CGEOLoader, "vs_GEO");
       LXx_ADD_SERVER (Saver,  CGEOSaver,  "vs_GEO");
}

This section exports the servers we create. In this case, we export a saver and a loader that take the contents of CGEOLoader and CGEOSaver respectively. They are both given the name vs_GEO.

Server Tags

LXtTagInfoDesc	 CGEOLoader::descInfo[] = {
       { LXsLOD_CLASSLIST,	LXa_SCENE	},
       { LXsLOD_DOSPATTERN,	"*.geo"		},
       { LXsSRV_USERNAME,	"VideoScape GEO"},
       { 0 }
};

Server tags define the format of the loader, its name and file pattern. The tags here indicate that the plugin is a scene loader that loads a mesh.

LXtTagInfoDesc	 CGEOSaver::descInfo[] = {
       { LXsSAV_OUTCLASS,	LXa_SCENE	},
       { LXsSAV_DOSTYPE,	"GEO"		},
       { LXsSRV_USERNAME,	"VideoScape GEO"},
       { 0 }
};

Similarly, since the saver in this plugin loads a mesh it is a scene saver

Implementation

       bool
CGEOLoader::sl_Recognize ()
{
       return lp_ReadLine () && (strcmp ("3DG1", line_buf) == 0);
}

Recognition method reads the first line and sees if it matches the sync pattern. Returns true for a match.

       bool
CGEOLoader::sl_ParseInit ()
{
       color_list.clear ();
       read_vrts = true;

       scene_build.AddMesh ();
       return lp_ReadLine ();
}

Parsing the recognized file (which has been reset to the start again) consists of three phases. The init method adds a mesh item to the scene and reads past the sync line.

        bool
CGEOLoader::sl_Parse (
        LxResult		*error)
{
        unsigned		 n, i, k;
        double			 x, y, z;
        string			 col;

        /*
         * One EOF this will return false which will terminate parsing.
         */
        if (!lp_ReadLine ())
                return false;

        /*
         * The first thing we read is the number of points.  We'll just loop
         * over that many lines here and create points for them all.  This sets
         * the flag false so that this only happens once.
         */
        if (read_vrts) {
                if (!PullNum (&n))
                        return false;

                for (i = 0; i < n; i++) {
                        if (!lp_ReadLine ())
                                return false;

                        if (!PullNum (&x) || !PullNum (&y) || !PullNum (&z))
                                return false;

                        scene_build.AddPoint (x, y, z);
                }

                read_vrts = false;
                return true;
        }

        /*
         * On subsequent calls to sl_Parse() we process one polygon at a time.
         * We first look for the number of vertices.  Those are read one at a
         * time and a polygon is created.
         */
        if (!PullNum (&n))
                return false;

        scene_build.StartPoly (LXiPTYP_FACE);

        for (i = 0; i < n; i++) {
                if (!PullNum (&k))
                        return false;

                scene_build.AddVertex (k);
        }

        k = scene_build.AddPolygon ();

        /*
         * The final value is the color name, which we store in a list and set
         * as the material tag.
         */
        PullWhite ();
        PullNonWhite (col);
        if (col.length ()) {
                color_list.push_back (col);
                scene_build.SetPolyTag (k, LXi_PTAG_MATR, col.c_str ());
        }
        return true;
}

The sl_Parse() method is called as long as it returns true.

       bool
CGEOLoader::sl_ParseDone ()
{
       list<string>::iterator	 itr;
       double			 rgb[3];
       int			 hex, i;

       color_list.sort ();
       color_list.unique ();

       for (itr = color_list.begin (); itr != color_list.end (); itr++) {
               hex = 0x808080;
               sscanf (itr->c_str (), "%x", &hex);
               for (i = 0; i < 3; i++) {
                       rgb[2 - i] = (hex & 0xFF) / 255.0;
                       hex = hex >> 8;
               }

               scene_build.AddMaterial (itr->c_str ());
               scene_build.SetChannel (LXsICHAN_ADVANCEDMATERIAL_DIFFCOL".R", rgb[0]);
               scene_build.SetChannel (LXsICHAN_ADVANCEDMATERIAL_DIFFCOL".G", rgb[1]);
               scene_build.SetChannel (LXsICHAN_ADVANCEDMATERIAL_DIFFCOL".B", rgb[2]);
       }
       return true;
}

The done method is called when parsing is complete. We collapse the list of colors that we created during parsing and create materials for them all.

       void
CGEOSaver::ss_Verify ()
{
       Message ("common", 2020);
       MessageArg (1, "GEO supports geometry from a single layer, and no texturing.");
}


The optional ss_Verify() method can be used to display a message to the user about what will happen to their data using this format. Ideally a real message table should be used to support translation, but common message 2020 allows for a general string. The scene could be examined at this point to determine if there was anything that would be lost.

        LxResult
CGEOSaver::ss_Save ()
{
        bool			 mesh;
        unsigned		 npts;

        /*
         * Count points in all meshes.
         */
        npts = 0;
        StartScan ();
        while (mesh = NextMesh ())
                npts += PointCount ();

        /*
         * Tabulate the colors of all the materials.
         */
        get_matr = true;
        StartScan ();
        while (mesh = NextMesh ())
                WritePolys ();

        GatherColors ();

        /*
         * Write the sync line and the number of points.
         */
        lf_Output ("3DG1");
        lf_Break ();
        lf_Output (npts);
        lf_Break ();

        /*
         * Write point positions.
         */
        pnt_count = 0;
        StartScan ();
        while (mesh = NextMesh ())
                WritePoints ();

        /*
         * Write polygons.
         */
        get_matr = false;
        StartScan ();
        while (mesh = NextMesh ())
                WritePolys ();

        /*
         * Clear any persistent state.
         */
        matr_color.clear ();
        pnt_index.clear ();
        return LXe_OK;
}

The save method performs the actual save. Note that this is called twice; first in a dummy mode with the format output disabled and then for real. In the dummy mode the WritePoints() and WritePolys() calls will not do anything except tabulate how many elements would be traversed in the real case. Because of the multiple passes and the fact that this same instance of the saver is used for all saving during a single session, all persistent states should be reset between uses.

       void
CGEOSaver::ss_Polygon ()
{
       if (get_matr) {
               const char *mask = PolyTag (LXi_PTAG_MATR);
               if (mask)
                       matr_color[mask] = 0;
               return;
       }

       unsigned		 i, n;
       char			 buf[32];

       n = PolyNumVerts ();
       lf_Output (n);

       for (i = 0; i < n; i++)
               lf_Output (pnt_index[PolyVertex (i)]);

       sprintf (buf, "0x%06X", matr_color[PolyTag (LXi_PTAG_MATR)]);
       lf_Output (buf);
       lf_Break ();
}

This is called for every polygon in the current mesh from WritePolys(). We make two passes through the polygons -- the first to collect the mask tags, and the second to actually write the polygons. Writing just writes the number of vertices, the vertex indicies, and the color for the polygon's material.

        void
CGEOSaver::GatherColors ()
{
        map<string,unsigned>::iterator it;
        const char		*mask;
        double			 rgb[3];
        unsigned		 col, cmp, i;

        for (it = matr_color.begin (); it != matr_color.end (); it++) {
                mask = it->first.c_str ();
                if (!ScanMask (mask)) {
                        matr_color[mask] = 0x808080;
                        continue;
                }

                while (NextLayer ()) {
                        if (strcmp (ItemType (), LXsITYPE_ADVANCEDMATERIAL))
                                continue;

                        rgb[0] = ChanFloat (LXsICHAN_ADVANCEDMATERIAL_DIFFCOL".R");
                        rgb[1] = ChanFloat (LXsICHAN_ADVANCEDMATERIAL_DIFFCOL".G");
                        rgb[2] = ChanFloat (LXsICHAN_ADVANCEDMATERIAL_DIFFCOL".B");

                        col = 0;
                        for (i = 0; i < 3; i++) {
                                if (rgb[i] <= 0.0)
                                        cmp = 0;
                                else if (rgb[i] >= 1.0)
                                        cmp = 255;
                                else
                                        cmp = (int) (rgb[i] * 255 + 0.5);

                                col = (col << 8) + cmp;
                        }

                        matr_color[mask] = col;
                }
        }
}


After the first pass through the polygons, we compute the color for each material tag that we stored in the map. This simply looks up the mask for the tag and looks through its layers. The first material that it finds we read the diffuse color. This can't be done while enumerating polygons because only one item scan can be performed at once and we're already scanning meshes.

       void
CGEOSaver::ss_Point ()
{
       float			 vec[3];

       PntPosition (vec);
       lf_Output (vec[0]);
       lf_Output (vec[1]);
       lf_Output (vec[2]);
       lf_Break ();

       pnt_index[PntID ()] = pnt_count++;
}

This method is called for every point during WritePoints(). We write the coordinates to a line and save the index of the point in our map.