Model.dtd

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  <!-- 
  The world defines everything that is in the physics model along with the
  parameters that are needed.
  -->
  <!ELEMENT world (gravity?, space*, object*, joint*)>
    <!-- The gravity element defines the constant force of gravity in this
    world. The gravity can have any direction and magnitude. The standard earth
    gravity would be x=0, y=0, z=-9.81 (assuming mks units)
    -->
    <!ELEMENT gravity EMPTY> 
      <!ATTLIST gravity x CDATA "0">
      <!ATTLIST gravity y CDATA "0">
      <!ATTLIST gravity z CDATA "0">
    <!-- The space is used for collisions, you can define multiple spaces in
    which the objects in each space will only collide with each other. If an
    object isn't in a space, then it won't collide with anything 
    -->
    <!ELEMENT space (object*)>
      <!ATTLIST space name CDATA #REQUIRED>
      <!-- An object is anything that is either simulated by the physics
      model or used for collisions. Every object has an ID attribute so that
      it is unique If an object has a transform, that transform is considered
      the center of the object relative to the world.
      -->
      <!ELEMENT object (body?, geom*, transform?)>
        <!ATTLIST object name CDATA #REQUIRED>
        <!-- A geom is added to an object for collision detection. When two
        geometries collide, they are pushed away from each other. The geom of
        an object determines what it looks like on the screen. A geom can be
        one of several types, (plane, ray, box, sphere, capped cylinder or a
        triangle mesh). A geom may optionally have a texture for use when
        drawing the object. If defined outside of a space, collision
        detection will not be performed. An object can have multiple
        geometries. They don't nessecarily have to be connected. A geometry
        can have a its own transform. This transform is relative to the
        transform of the object
        -->
        <!ELEMENT geom (texture?, (plane|box|sphere|cylender|trimesh), 
                        transform?)>
          <!-- A geometry can hava a name specified. If not specified, a name
          will be created for the geometry -->
          <!ATTLIST geom name CDATA #IMPLIED>
          <!-- A texture file containing an image that should be drawn on
          this geometry 
          -->
          <!ELEMENT texture EMPTY>
            <!ATTLIST texture filename CDATA #REQUIRED>
          <!-- A plane is defined with the equation a*x+b*y+c*z=d -->
          <!ELEMENT plane EMPTY>
            <!ATTLIST plane a CDATA #REQUIRED>
            <!ATTLIST plane b CDATA #REQUIRED>
            <!ATTLIST plane c CDATA #REQUIRED>
            <!ATTLIST plane d CDATA #REQUIRED>
          <!-- A box is defined as a set of three lenghts. The position of
          the box is the center of mass (posx + lengthx/2, ...) -->
          <!ELEMENT box EMPTY>
            <!ATTLIST box x CDATA #REQUIRED>
            <!ATTLIST box y CDATA #REQUIRED>
            <!ATTLIST box z CDATA #REQUIRED>
          <!-- A sphere is defined by its radius. The position of a sphere
          gives the location of the center -->
          <!ELEMENT sphere EMPTY>
            <!ATTLIST sphere radius CDATA #REQUIRED>
          <!-- A cylinder is defined as a radius and length. The position of
          the cylinder gives the location of the center of mass. -->
          <!ELEMENT cylinder EMPTY>
            <!ATTLIST cylinder radius CDATA #REQUIRED>
            <!ATTLIST cylinder height CDATA #REQUIRED>
          <!-- A trimesh is defined as two lists. One of verticies which are
          specified by x/y/z position and a second list of triangles. The
          triangles are defined by three vertex numbers. The vertex index is
          the order that the vertexes are defined in the vertices list
          -->
          <!ELEMENT trimesh (vertices, triangles)>
            <!ELEMENT vertices (vertex+)>
              <!ELEMENT vertex EMPTY>
                <!ATTLIST vertex x CDATA #REQUIRED>
                <!ATTLIST vertex y CDATA #REQUIRED>
                <!ATTLIST vertex z CDATA #REQUIRED>
            <!ELEMENT triangles (triangle+)>
              <!ELEMENT triangle EMPTY>
                <!ATTLIST triangle v1 CDATA #REQUIRED>
                <!ATTLIST triangle v2 CDATA #REQUIRED>
                <!ATTLIST triangle v3 CDATA #REQUIRED>
          <!-- A transform is a generic manipulation of the position and
          rotation of an item. The transform is applied to the object only
          and is relative to the transform of the parent object. So an
          object could have a transfrom that sets the position relative to
          the world and a geometry could have an additional transform that
          sets its position relative to the object.
          Sub-Elements:
          <position> <rotation>
          -->
          <!ELEMENT transform (position?, (rotation|quaternion)?)>
            <!ELEMENT position EMPTY>
              <!ATTLIST position x CDATA "0">
              <!ATTLIST position y CDATA "0">
              <!ATTLIST position z CDATA "0">
            <!ELEMENT rotation EMPTY>
              <!ATTLIST rotation x CDATA #REQUIRED>
              <!ATTLIST rotation y CDATA #REQUIRED>
              <!ATTLIST rotation z CDATA #REQUIRED>
            <!ELEMENT quaternion EMPTY>
              <!ATTLIST quaternion x CDATA #REQUIRED>
              <!ATTLIST quaternion y CDATA #REQUIRED>
              <!ATTLIST quaternion z CDATA #REQUIRED>
              <!ATTLIST quaternion angle CDATA #REQUIRED>
        <!-- A body is added to an object for physics modeling. If an object
        doesn't have a body, then it is completely stationary as though it
        were un-effected by gravity and other objects. If an object is meant
        to be stationary (like a wall or the floor) then it shouldn't have a
        body. -->
        <!ELEMENT body (mass)>
          <!-- A body must have one mass. The mass can be made up of other
          masses, be one of the pre-defined types (box, sphere,
          cylinder, and capped cylinder), or a generic center of mass and
          moment of inertia matrix. All of the masses are added to the body
          recursively. At each level, the total mass can be set, this will
          set the mass of all the items include in that mass to the given
          value
          -->
          <!ELEMENT mass ((mass*|mass_shape|mass_struct), transform?)>
            <!ATTLIST mass total CDATA #IMPLIED>
            <!-- A mass shape is a pre-defined mass distribution. By default,
            we assume that a mass distribution has a density of 1.0 unless
            the density or total mass is defined. The mass shapes are defined
            exactly like the geometries with the same name -->
            <!ELEMENT mass_shape (box|sphere)>
              <!ATTLIST mass_shape density CDATA "1.0">
              <!ATTLIST mass_shape total CDATA #IMPLIED>
            <!-- A mass struct allows you to set the exact center and moment
            of inertia matrix of the mass. Use this if your mass doesn't look
            like one of the pre-defined types. The center of mass and inertia
            maxtix must be given. The inertia matrix is defined as
            ( m00, m01, m02 )
            ( m10, m11, m12 )
            ( m20, m21, m22 )
            However, you only specify the upper right and diagonal portion of
            the matrix since it is symetric
            -->
            <!ELEMENT mass_struct (center, inertia)>
              <!ATTLIST mass_struct total CDATA #REQUIRED>
              <!ELEMENT center EMPTY>
                <!ATTLIST center x CDATA #REQUIRED>
                <!ATTLIST center y CDATA #REQUIRED>
                <!ATTLIST center z CDATA #REQUIRED>
              <!ELEMENT inertia EMPTY>
                <!ATTLIST inertia m00 CDATA #REQUIRED>
                <!ATTLIST inertia m01 CDATA #REQUIRED>
                <!ATTLIST inertia m02 CDATA #REQUIRED>
                <!ATTLIST inertia m11 CDATA #REQUIRED>
                <!ATTLIST inertia m12 CDATA #REQUIRED>
                <!ATTLIST inertia m22 CDATA #REQUIRED>
    <!-- Joints are connections between bodies. Geometries without a body are
    immobile so there is no point connecting them with a joint. However, a
    single body can be connected with a joint. The other body is considered to
    be a fixed point. Joints must be defined after the objects they are
    connecting -->
    <!ELEMENT joint (hinge|ball|slider)>
      <!ATTLIST joint name CDATA #REQUIRED>
      <!ATTLIST joint body1 CDATA #REQUIRED>
      <!ATTLIST joint body2 CDATA #IMPLIED>
      <!-- The range of a joint can be set, along with the maximum amount of
      force that this moter can apply. Note that this only applies to a moter,
      and even for them, the maximum can be exceded if needed to maintain the
      low and high stop points. -->
      <!ELEMENT hinge (position, axis)>
        <!ATTLIST hinge lowstop CDATA #IMPLIED>
        <!ATTLIST hinge highstop CDATA #IMPLIED>
        <!ATTLIST hinge force CDATA #IMPLIED>
        <!ATTLIST hinge velocity CDATA #IMPLIED>
        <!ELEMENT axis EMPTY>
          <!ATTLIST axis x CDATA #REQUIRED>
          <!ATTLIST axis y CDATA #REQUIRED>
          <!ATTLIST axis z CDATA #REQUIRED>
      <!ELEMENT ball (position)>
      <!ELEMENT slider (position, axis)>

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