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It is also possible to draw 3D symbols using OpenGL commands to draw triangles, lines, etc.

A simple way is to have the shape stored in a file with GiD mesh ASCII format

These symbols can be drawn oriented by a vector (e.g. typical case of a force), or by a 3x3 rotation matrix (for a more special case), with a scale factor depending on some field, related to global XYZ axis or local axis of curves or surfaces (using its tangent and normal vectors)

We provide a gid_draw_opengl Tcl package with some interesting procs to facilitate common tasks and usual shapes like an arrow to represent a force, a double T section of a beam, etc.

The code is at <gid>\scripts\gid_draw_opengl

(the subfolder symbols has some .msh files)

See the problemtype <gid>\problemtypes\Examples\customlib\condition_symbols.gid

there is a condition

  <condition n="self_weight_3d" pn="Self weight" ov="volume" ovm="" icon="select" help="Set gravity value giving a Modulus and a Direction" groups_icon="groupCreated">
    <symbol proc="ConditionSymbols::draw_selfweight" orientation="global"/>
    <value n="modulus" pn="Gravity" v="9.81" units="m/s^2" unit_magnitude="Acceleration" help="Gravity acceleration value" string_is="double" icon="data"/>
    <value n="direction" pn="Direction" v="0.0,0.0,-1.0" fieldtype="vector" dimensions="3" help="The resultant unit vector is considered" icon="data"/>
  </condition>

its <symbol> node has attributes

proc="ConditionSymbols::draw_selfweight"

orientation="global"

and the proc is defined as

proc ConditionSymbols::draw_selfweight { values_list } {
    foreach item $values_list {
        lassign $item key value unit
        set data($key) $value
        #set unit($key) $unit
    }
    set modulus $data(modulus)
    set direction [split $data(direction) ,]
    set opposite_direction [math::linearalgebra::scale_vect -1.0 $direction]
    set full_filename [file join [gid_filesystem::get_folder_standard scripts] gid_draw_opengl symbols selfweight.msh]
    set color_lines black
    set color_surfaces blue
    set list_id [gid_draw_opengl::create_opengl_list_from_file_mesh_oriented_z_direction $full_filename $color_lines $color_surfaces $opposite_direction]
    return $list_id
}

the values_list provide the values of each specific condition instance, first are extracted the ones named ‘modulus’ and ‘direction’ and then is called the predefined proc

gid_draw_opengl::create_opengl_list_from_file_mesh_oriented_z_direction

that read the mesh from the path the a mesh file selfweight.msh and draw it with OpenGL commands, creating an drawing list for better performance and return its id

Then creating a model, loading this problemtype, and assigning this condition to a volume, can be drawn for example with the contextual menu: Draw symbols

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and the shape is drawn oriented with the direction 0,0,-1 (global direction -Z)

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