Support image/ktx format for textures.

PiperOrigin-RevId: 761926074
Change-Id: I6a312634b5bdc706ea5166bc3b2be273e14c1c8a

doc/XMLreference.rst

@@ -1464,16 +1464,19 @@ still be specified here but this functionality is now deprecated and will be rem
 :el-prefix:`asset/` |-| **texture** (*)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-| This element creates a texture asset, which is then referenced from a :ref:`material <asset-material>` asset, which is
-  finally referenced from a model element that needs to be textured. MuJoCo provides access to the texture mapping
-  mechanism in OpenGL. Texture coordinates are generated automatically in GL_OBJECT_PLANE mode, using either 2D or cube
-  mapping. MIP maps are always enabled in GL_LINEAR_MIPMAP_LINEAR mode. The texture color is combined with the object
-  color in GL_MODULATE mode. The texture data can be loaded from PNG files, with provisions for loading cube and skybox
-  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.
-| A second file format is supported for loading textures, in addition to PNG. If the file name extension is
-  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 this format. This is a custom binary file format, containing the following data:
+   This element creates a texture asset, which is then referenced from a :ref:`material <asset-material>` asset, which
+   is finally referenced from a model element that needs to be textured.
+
+   The texture data can be loaded from files or 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. Provisions are provided for loading cube and skybox textures from individual image files.
+
+   Currently, three file formats are supported for loading textures: PNG, KTX, and a custom MuJoCo texture format. The
+   loader will use the extension of the file name to determine which format to use, defaulting to the custom format if
+   the extension is not recognized. Alternatively, the content_type attribute can be used to specify the format
+   explicitly. Only ``image/png``, ``image/ktx``, or ``image/vnd.mujoco.texture`` are supported.
+
+   The custom MuJoCo format is assumed to be a binary file containing the following data:
 
 .. code:: Text
 
@@ -1537,8 +1540,8 @@ still be specified here but this functionality is now deprecated and will be rem
 :at:`content_type`: :at-val:`string, optional`
    If the file attribute is specified, then this sets the
    `Media Type <https://www.iana.org/assignments/media-types/media-types.xhtml>`_ (formerly known as MIME types) of the
-   file to be loaded. Any filename extensions will be ignored.  Currently ``image/png`` and ``image/vnd.mujoco.texture``
-   are supported.
+   file to be loaded. Any filename extensions will be ignored.  Currently ``image/png``, ``image/ktx``, and
+   ``image/vnd.mujoco.texture`` are supported.
 
 .. _asset-texture-file:
 
@@ -1786,11 +1789,11 @@ properties are grouped together.
 .. _asset-material-rgba:
 
 :at:`rgba`: :at-val:`real(4), "1 1 1 1"`
-   Color and transparency of the material. All components should be in the range [0 1]. Note that textures are applied
-   in GL_MODULATE mode, meaning that the texture color and the color specified here are multiplied component-wise. Thus
-   the default value of "1 1 1 1" has the effect of leaving the texture unchanged. When the material is applied to a
-   model element which defines its own local rgba attribute, the local definition has precedence. Note that this "local"
-   definition could in fact come from a defaults class. The remaining material properties always apply.
+   Color and transparency of the material. All components should be in the range [0 1]. Note that the texture color (if
+   assigned) and the color specified here are multiplied component-wise. Thus the default value of "1 1 1 1" has the
+   effect of leaving the texture unchanged. When the material is applied to a model element which defines its own local
+   rgba attribute, the local definition has precedence. Note that this "local" definition could in fact come from a
+   defaults class. The remaining material properties always apply.
 
 .. _material-layer:
 

src/engine/engine_io.c

@@ -2406,7 +2406,7 @@ const char* mj_validateReferences(const mjModel* m) {
     }
   }
   for (int i=0; i < m->ntex; i++) {
-    int tex_adr = m->tex_adr[i] + 3*m->tex_height[i]*m->tex_width[i];
+    int tex_adr = m->tex_adr[i] + m->tex_nchannel[i]*m->tex_height[i]*m->tex_width[i];
     if (tex_adr > m->ntexdata || m->tex_adr[i] < 0) {
       return "Invalid model: tex_adr out of bounds.";
     }

src/user/user_objects.cc

@@ -4283,6 +4283,28 @@ void mjCTexture::LoadPNG(mjResource* resource,
   image = png_image.MoveData();
 }
 
+// load KTX file
+void mjCTexture::LoadKTX(mjResource* resource,
+                         std::vector<unsigned char>& image, unsigned int& w,
+                        unsigned int& h, bool& is_srgb) {
+  const void* buffer = 0;
+  int buffer_sz = mju_readResource(resource, &buffer);
+
+  // still not found
+  if (buffer_sz < 0) {
+    throw mjCError(this, "could not read texture file '%s'", resource->name);
+  } else if (!buffer_sz) {
+    throw mjCError(this, "texture file is empty: '%s'", resource->name);
+  }
+
+  w = buffer_sz;
+  h = 1;
+  is_srgb = false;
+
+  image.resize(buffer_sz);
+  memcpy(image.data(), buffer, buffer_sz);
+}
+
 // load custom file
 void mjCTexture::LoadCustom(mjResource* resource,
                             std::vector<unsigned char>& image,
@@ -4336,7 +4358,7 @@ void mjCTexture::LoadFlip(std::string filename, const mjVFS* vfs,
     asset_type = "image/vnd.mujoco.texture";
   }
 
-  if (asset_type != "image/png" && asset_type != "image/vnd.mujoco.texture") {
+  if (asset_type != "image/png" && asset_type != "image/ktx" && asset_type != "image/vnd.mujoco.texture") {
     throw mjCError(this, "unsupported content type: '%s'", asset_type.c_str());
   }
 
@@ -4345,6 +4367,11 @@ void mjCTexture::LoadFlip(std::string filename, const mjVFS* vfs,
   try {
     if (asset_type == "image/png") {
       LoadPNG(resource, image, w, h, is_srgb);
+    } else if (asset_type == "image/ktx") {
+      if (hflip || vflip) {
+        throw mjCError(this, "cannot flip KTX textures");
+      }
+      LoadKTX(resource, image, w, h, is_srgb);
     } else {
       LoadCustom(resource, image, w, h, is_srgb);
     }

src/user/user_objects.h

@@ -1333,6 +1333,9 @@ class mjCTexture : public mjCTexture_, private mjsTexture {
   void LoadPNG(mjResource* resource,
                std::vector<unsigned char>& image,
                unsigned int& w, unsigned int& h, bool& is_srgb);
+  void LoadKTX(mjResource* resource,
+               std::vector<unsigned char>& image,
+               unsigned int& w, unsigned int& h, bool& is_srgb);
   void LoadCustom(mjResource* resource,
                   std::vector<unsigned char>& image,
                   unsigned int& w, unsigned int& h, bool& is_srgb);