Re: XML was RE: [GD-General] RE: A portable preferences library

[Jorrit T. <Jor...@uz...>]

Alen Ladavac wrote:

>>We use XML a lot in Crystal Space (http://crystal.sf.net). It does tend
>>to give very
>>big files but we also found that it doesn't matter.
>>    
>>
>
>Just how big that is? Can you please compare size of a mesh in XML format to
>the same mesh in, say, .3ds or .lwo?
>  
>
I didn't make the map files so I don't have any of the model files that
were used but I can show you an example of a simple mesh in CS:

    <meshobj name="cube">
       <plugin>thing</plugin>
       <params>
          <v x="-1" y="0" z="1" />
          <v x="0" y="0" z="1" />
          ... (more vertices follow)
          <material>brick</material>
          <p> <v>0</v> <v>1</v> <v>2</v> </p>
          <p> <v>3</v> <v>2</v> <v>4</v> <v>5</v> </p>
          ... (more polygons follow)
       </params>
    </meshobj>

So this is indeed pretty verbose.

>  
>
>>CS supports reading
>>from ZIP files
>>so map files are usually placed in compressed archives. XML compresses very
>>well (due to the high redundancy) so the size disadvantage nearly completely
>>disappears in that case.
>>    
>>
>
>Can you also please compare size of a zipped XML mesh and a zipped .3ds, or
>.lwo or similar format of the same mesh?
>  
>
Sorry. Don't have the needed models to do that.

>Also, in case that zipping really does remove the redundancy well enough to
>allow us to ignore the size difference, did you check your effective loading
>throughput? Meaning how much MB/sec can you read from the disk. To make sure
>that the parser is not slowing your loading. Ideally, you should be limited by
>the transfer rate of the disk, not by the CPU.
>  
>
The PlaneShift game (made with CS) has about 25 megabytes (uncompressed) 
of XML files (aggregated
in four big files) of level data. On my Linux system at home (an Athlon 
XP2000) the levels load
in about 16-20 seconds. That includes the following operations:
    - Extracting the XML data from the ZIP.
    - Parsing of XML.
    - Creation of all objects.
    - Loading of all textures used in the levels and preparing them for 
use with OpenGL.
    - Creation of the kdtree for the visibility culler.
    - Loading of the lightmap data for the 100000 polygons that are in 
those levels.
    - Creation of oriented bounding boxes for collision detection (this 
is the most
      time consuming operation of all things mentioned here).

I don't have seperate numbers for XML parsing but it is a relatively 
small part
of the entire thing. Of course this is done using a hand-made XML parser 
which
is very lean and mean and is optimized specifically towards reading.

Greetings,