XEG specification

Specification Details

node types

node type properties property type (range) standard value notes

Node transform - 16 floats identity matrix color - 3 floats (0.0 - 1.0) 0.0, 0.0, 0.0

Sphere transform - 16 floats identity matrix color - 3 floats (0.0 - 1.0) 0.0, 0.0, 0.0 radius float 1.0

Box transform - 16 floats identity matrix color - 3 floats (0.0 - 1.0) 0.0, 0.0, 0.0 width float 1.0 depth float 1.0 height float 1.0

Cone transform - 16 floats identity matrix color - 3 floats (0.0 - 1.0) 0.0, 0.0, 0.0 radius float 1.0 height float 1.0 bottom_open boolean false

Cylinder transform - 16 floats identity matrix color - 3 floats (0.0 - 1.0) 0.0, 0.0, 0.0 radius float 1.0 height float 1.0 bottom_open boolean false top_open boolean false

Frustum transform - 16 floats identity matrix color - 3 floats (0.0 - 1.0) 0.0, 0.0, 0.0 radius float 1.0 bottom_radius = radius height float 1.0 taper float 0.5 top_radius = radius * taper bottom_open boolean false top_open boolean false

new node types

Mesh transform - 16 floats identity matrix color - 3 floats (0.0 - 1.0) 0.0, 0.0, 0.0 indices <list_of_int> [] coords <list_of_float> [] normals <list_of_float> [] texcoords <list_of_float> []

• coords is a set of 3D coordinates

• normals is a set of 3D normal vectors at the vertices

• texcoords is set of 2D texture coordinates (at the vertices)

• index field references the coords, normals and texcoords

• a mesh consists of triangles, so every three indices describes a polygon

• a index n references as follows:

• the vertices in the coords field 3n+0, 3n+1, 3*n+2

  • the normals in the normals field 3n+0, 3n+1, 3*n+2
  • the texture coordinates in the texcoords field 2n+0, 2n+1

• the coords field shall contain three times as many vertices as indices are given

• the normals field shall contain three times as many normals as indices are given

• the texcoords field shall contain two times as many texture coordinates as indices are given

• the ordering of the vertex coordinates shall be counterclockwise

• a mesh is not solid, so each polygon shall be visible regardless of the viewing direction

  Axiom - - -

    - no properties
  

  F transform - 16 floats identity matrix color - 3 floats (0.0 - 1.0) 0.0, 0.0, 0.0 length float 1 diameter float -1 turtle_color int (0 - 15) -1

    - it is always the length property used
    - if the diameter is not given or -1, then the turtle state is used (e.g. set with D(x))
    - if the color is not given or -1, then the turtle state is used (e.g. set with P(x))
  

  F0 transform - 16 floats identity matrix color - 3 floats (0.0 - 1.0) 0.0, 0.0, 0.0

    - the turtle state is used to set the appearance (length, diameter, color)
  

  M transform - 16 floats identity matrix length float 1

    - movement
  

  M0 transform - 16 floats identity matrix

    - the turtle state is used to set the length of movement
  

  RL angle float 0

    - a rotation about the x-axis specified in degrees
  

  RU angle float 0

    - a rotation about the negative y-axis specified in degrees
  

  RH angle float 0

    - a rotation about the z-axis specified in degrees
  

  RV strength float 0

    - gravitropism
  

  RG - - -

    - no properties
    - maximal gravitropism such that local z-direction points downwards
  

  AdjustLU - - -

    - no properties
    - rotate around local z-axis such that local y-axis points upwards as far as possible
  

  L length float 1

    - set the turtle state to the given length
  

  D diameter float 0.1

    - set the turtle state to the given diameter
  

  P color int (0 - 15) 14

    - set the turtle state to the given color
    - the color field specifies the color index in the palette of the EGA graphics standard
    	0	black
    	1	blue
    	2	green
    	3	cyan
    	4	red
    	5	magenta
    	6	brown
    	7	light gray
    	8	dark gray
    	9	bright blue
    	10	bright green
    	11	bright cyan
    	12	bright red
    	13	bright magenta
    	14	yellow
    	15	white