add content_type to model in the XML schema.

PiperOrigin-RevId: 670961443
Change-Id: I98cd6bb61b50029cdd4f5b31e23d268989d136da

src/render/render_context.c

@@ -1382,8 +1382,16 @@ void mjr_uploadTexture(const mjModel* m, const mjrContext* con, int texid) {
     glTexGenfv(GL_T, GL_OBJECT_PLANE, plane);
 
     // assign data
-    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, m->tex_width[texid], m->tex_height[texid], 0,
-                 GL_RGB, GL_UNSIGNED_BYTE, m->tex_data + m->tex_adr[texid]);
+    int type = 0;
+    if (m->tex_nchannel[texid] == 3) {
+      type = GL_RGB;
+    } else if (m->tex_nchannel[texid] == 4) {
+      type = GL_RGBA;
+    } else {
+      mju_error("Number of channels not supported: %d", m->tex_nchannel[texid]);
+    }
+    glTexImage2D(GL_TEXTURE_2D, 0, type, m->tex_width[texid], m->tex_height[texid], 0,
+                 type, GL_UNSIGNED_BYTE, m->tex_data + m->tex_adr[texid]);
 
     // generate mipmaps
     glGenerateMipmap(GL_TEXTURE_2D);

src/user/user_model.cc

@@ -1547,7 +1547,7 @@ void mjCModel::SetSizes() {
   for (int i=0; i<nhfield; i++) nhfielddata += hfields_[i]->nrow * hfields_[i]->ncol;
 
   // ntexdata
-  for (int i=0; i<ntex; i++) ntexdata += 3 * textures_[i]->width * textures_[i]->height;
+  for (int i=0; i<ntex; i++) ntexdata += textures_[i]->nchannel * textures_[i]->width * textures_[i]->height;
 
   // nwrap
   for (int i=0; i<ntendon; i++) nwrap += (int)tendons_[i]->path.size();

src/xml/xml_native_reader.cc

@@ -258,7 +258,7 @@ const char* MJCF[nMJCF][mjXATTRNUM] = {
             {"rgba", "?", "1", "texture"},
             {"orm", "?", "1", "texture"},
         {">"},
-        {"model", "*", "2", "name", "file"},
+        {"model", "*", "3", "name", "file", "content_type"},
     {">"},
 
     {"body", "R", "11", "name", "childclass", "pos", "quat", "mocap",
@@ -3306,11 +3306,22 @@ void mjXReader::Asset(XMLElement* section, const mjVFS* vfs) {
 
     // model sub-element
     else if (name=="model") {
-      auto filename = modelfiledir_ + ReadAttrFile(elem, "file", vfs).value();
+      string content_type;
+      if (!ReadAttrTxt(elem, "content_type", content_type)) {
+        content_type = "text/xml";
+      }
 
       // parse the child
+      mjSpec* child = nullptr;
       std::array<char, 1024> error;
-      mjSpec* child = mj_parseXML(filename.c_str(), vfs, error.data(), error.size());
+      auto filename = modelfiledir_ + ReadAttrFile(elem, "file", vfs).value();
+
+      if (content_type == "text/xml") {
+        child = mj_parseXML(filename.c_str(), vfs, error.data(), error.size());
+      } else {
+        throw mjXError(elem, "unsupported content_type: %s", content_type.c_str());
+      }
+
       if (!child) {
         throw mjXError(elem, "could not parse model file with error: %s", error.data());
       }