Add content_type attribute that takes a MIME type to specify the file contents for meshes, hfields, and textures.

PiperOrigin-RevId: 549302344
Change-Id: I30a8adfef5b5d87bb20479329f3396892f5137ff

doc/XMLreference.rst

@@ -2081,7 +2081,10 @@ This adds an element to the tuple.
 
 This is a grouping element for defining assets. It does not have attributes. Assets are created in the model so that
 they can be referenced from other model elements; recall the discussion of :ref:`Assets <Assets>` in the Overview
-chapter.
+chapter. Assets opened from a file can be identified in two different ways: filename extensions or the ``content_type``
+attribute. MuJoCo will attempt to open a file specified by the content type provided, and only defaults to the filename
+extension if no ``content_type`` attribute is specified. The content type is ignored if the asset isn't loaded from a
+file.
 
 
 .. _asset-texture:
@@ -2097,8 +2100,8 @@ chapter.
   textures. Alternatively the data can be generated by the compiler as a procedural texture. Because different texture
   types require different parameters, only a subset of the attributes below are used for any given texture.
 | MuJoCo 2.0 introduced a second file format for loading textures, in addition to PNG. If the file name extension is
-  different from .png or .PNG, MuJoCo assumes that the texture is in the new format. This is a custom binary file
-  format, containing the following data:
+  different from .png or .PNG, or if the ``content_type`` attribute is set to ``image/vnd.mujoco.texture``, then MuJoCo
+  assumes that the texture is in the new format. This is a custom binary file format, containing the following data:
 
 .. code:: Text
 
@@ -2153,6 +2156,13 @@ chapter.
    texrepeat attribute of :ref:`material <asset-material>`. The data can be loaded from a singlefile or created
    procedurally.
 
+.. _asset-texture-content_type:
+
+:at:`content_type`: :at-val:`string, optional`
+   If the file attribute is specified, then this sets the `MIME <https://en.wikipedia.org/wiki/MIME>`_ type of the file
+   to be loaded. Any filename extensions will be ignored.  Currently ``image/png`` and ``image/vnd.mujoco.texture`` are
+   supported.
+
 .. _asset-texture-file:
 
 :at:`file`: :at-val:`string, optional`
@@ -2335,6 +2345,13 @@ also known as terrain map, is a 2D matrix of elevation data. The data can be spe
    Name of the height field, used for referencing. If the name is omitted and a file name is specified, the height field
    name equals the file name without the path and extension.
 
+.. _asset-hfield-content_type:
+
+:at:`content_type`: :at-val: `string, optional`
+   If the file attribute is specified, then this sets the `MIME <https://en.wikipedia.org/wiki/MIME>`_ type of the file
+   to be loaded. Any filename extensions will be overloaded.  Currently ``image/png`` and ``image/vnd.mujoco.hfield``
+   are supported.
+
 .. _asset-hfield-file:
 
 :at:`file`: :at-val:`string, optional`
@@ -2500,12 +2517,19 @@ The full list of processing steps applied by the compiler to each mesh is as fol
 :at:`class`: :at-val:`string, optional`
    Defaults class for setting unspecified attributes (only scale in this case).
 
+.. _asset-mesh-content_type:
+
+:at:`content_type`: :at-val:`string, optional`
+   If the file attribute is specified, then this sets the `MIME <https://en.wikipedia.org/wiki/MIME>`_ type of the file
+   to be loaded. Any filename extensions will be overloaded.  Currently ``model/vnd.mujoco.msh``, ``model/obj``, and
+   ``model/stl`` are supported.
+
 .. _asset-mesh-file:
 
 :at:`file`: :at-val:`string, optional`
    The file from which the mesh will be loaded. The path is determined as described in the meshdir attribute of
-   :ref:`compiler <compiler>`. The file extension must be "stl" or "msh" (not case sensitive) specifying the file type.
-   If the file name is omitted, the vertex attribute becomes required.
+   :ref:`compiler <compiler>`. The file extension must be "stl", "msh", or "obj" (not case sensitive) specifying the
+   file type.  If the file name is omitted, the vertex attribute becomes required.
 
 .. _asset-mesh-scale: