Gazebo material format

[Tacha-S]

SDF allows the use of script within the material definition, and in gz simulator, the material tag inside the gazebo tag also supports script.
However, when specifying it as follows, gz simulator requests a string upon startup.

http://sdformat.org/spec?ver=1.12&elem=material

sdformat/src/parser_urdf.cc

Lines 1317 to 1321 in 2b583cb

	// material
	if (strcmp(childElem->Name(), "material") == 0)
	{
	sdf->material = GetKeyValueAsString(childElem);
	}

<gazebo reference="link1">
      <material>
        <script>
          <uri>file://media/materials/scripts/gazebo.material</uri>
          <name>Gazebo/Black</name>
        </script>
      </material>
    </gazebo>

Environment

• OS Version: Ubuntu 24.04
• Source or binary build: Binary 14.6.0

Description

• Expected behavior:
  NO warning.
• Actual behavior:
  Attribute value string not set is shown.

Steps to reproduce

1. Set material color to a link

<gazebo reference="link1">
      <material>
        <script>
          <uri>file://media/materials/scripts/gazebo.material</uri>
          <name>Gazebo/Black</name>
        </script>
      </material>
    </gazebo>

2. launch gz server

Output

[gazebo-1] Warning [parser_urdf.cc:1220] Attribute value string not set
[gazebo-1] Warning [parser_urdf.cc:1220] Attribute value string not set
[gazebo-1] Warning [parser_urdf.cc:1220] Attribute value string not set
[gazebo-1] Warning [parser_urdf.cc:1220] Attribute value string not set
[gazebo-1] Warning [parser_urdf.cc:1220] Attribute value string not set
[gazebo-1] Warning [parser_urdf.cc:1220] Attribute value string not set
[gazebo-1] Warning [parser_urdf.cc:1220] Attribute value string not set
[gazebo-1] Warning [parser_urdf.cc:1220] Attribute value string not set
[gazebo-1] Warning [parser_urdf.cc:1220] Attribute value string not set
[gazebo-1] Warning [parser_urdf.cc:1220] Attribute value string not set
[gazebo-1] Warning [parser_urdf.cc:1220] Attribute value string not set

[azeey]

Can you please provide a full .sdf or .urdf file to try?

[Tacha-S]

example.urdf

<?xml version="1.0" encoding="UTF-8"?>
<robot xmlns:xacro="http://www.ros.org/wiki/xacro" name="bot">
  <link name="base_footprint"/>
  <joint name="base_joint" type="fixed">
    <parent link="base_footprint"/>
    <child link="base_link"/>
    <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/>
  </joint>

  <link name="base_link">
    <visual>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <geometry>
        <box size="1 1 1"/>
      </geometry>
      <material name="white">
        <color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <geometry>
        <box size="1 1 1"/>
      </geometry>
    </collision>
    <inertial>
      <mass value="1"/>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <inertia ixx="0.1" ixy="0.0" ixz="0.0" iyy="0.1" iyz="0.0" izz="0.1"/>
    </inertial>
  </link>
  <gazebo reference="base_link">
    <material>
      <script>
        <uri>file://media/materials/scripts/gazebo.material</uri>
        <name>Gazebo/Black</name>
      </script>
    </material>
  </gazebo>
</robot>

1. launch gz server
   gz sim empty.sdf
2. spawn example urdf
   gz service -s /world/empty/create --reqtype gz.msgs.EntityFactory --reptype gz.msgs.Boolean --timeout 1000 --req 'sdf_filename: "/path/to/example.urdf", name: "bot"'

[oscar-lima]

The new syntax for materials in Gazebo harmonic, see: https://gazebosim.org/api/sim/9/migrationsdf.html#:~:text=Materials also has the same problem, according to that migration guide to make our models compatible with both simulators one should do:

<material>
  <ambient>1 0 0 1</ambient>
  <diffuse>1 0 0 1</diffuse>
  <specular>0.1 0.1 0.1 1</specular>
</material>

but that triggers the warning: "Attribute value string not set"

The problem is in: https://github.com/gazebosim/sdformat/blob/sdf15/src/parser_urdf.cc#L1204

The parser first checks for an attribute explicitly named "value", e.g. <material value="Gazebo/DarkGrey"/>

Since it doesn't find a "value" attribute, it proceeds to the else if block. It checks for a child node, which it finds (<ambient>). However, it then checks if that child is a text node _elem->FirstChild()->ToText(). The tag is another element (XMLElement), not a text node, so this check also fails.

Therefore as (Gazebo harmonic) users we are trapped with a warning, if you go for:
<material value="Gazebo/DarkGrey"/> or <material>Gazebo/DarkGrey</material> you don't get the "Attribute value string not set" warning but you get the "Gazebo does not support Ogre material scripts. See https://gazebosim.org/api/sim/8/migrationsdf.html#:~:text=Materials for details." warning. If you click on the link and try to migrate away from Ogre you get a "Attribute value string not set" warning.