Make 3 the default number of channels in mjsTexture.

PiperOrigin-RevId: 679521155
Change-Id: Ie6c962e75983c8bf8323170338b3d480be3a1117

src/user/user_init.c

@@ -274,6 +274,7 @@ void mjs_defaultTexture(mjsTexture* texture) {
   texture->rgb2[0] = texture->rgb2[1] = texture->rgb2[2] = 0.5;
   texture->random = 0.01;
   texture->gridsize[0] = texture->gridsize[1] = 1;
+  texture->nchannel = 3;
   char defaultlayout[sizeof(texture->gridlayout)] = "............";
   strncpy(texture->gridlayout, defaultlayout, sizeof(texture->gridlayout));
 }

src/xml/xml_native_reader.cc

@@ -3236,9 +3236,7 @@ void mjXReader::Asset(XMLElement* section, const mjVFS* vfs) {
       }
       ReadAttrInt(elem, "width", &texture->width);
       ReadAttrInt(elem, "height", &texture->height);
-      if (!ReadAttrInt(elem, "nchannel", &texture->nchannel)) {
-        texture->nchannel = 3;
-      }
+      ReadAttrInt(elem, "nchannel", &texture->nchannel);
       ReadAttr(elem, "rgb1", 3, texture->rgb1, text);
       ReadAttr(elem, "rgb2", 3, texture->rgb2, text);
       ReadAttr(elem, "markrgb", 3, texture->markrgb, text);

test/user/user_api_test.cc

@@ -1254,5 +1254,35 @@ TEST_F(MujocoTest, AttachUnnamedAssets) {
   mj_deleteModel(model);
 }
 
+TEST_F(MujocoTest, InitTexture) {
+  mjSpec* spec = mj_makeSpec();
+  EXPECT_THAT(spec, NotNull());
+
+  mjsTexture* texture = mjs_addTexture(spec);
+  mjs_setString(texture->name, "checker");
+  texture->type = mjTEXTURE_CUBE;
+  texture->builtin = mjBUILTIN_CHECKER;
+  texture->width = 300;
+  texture->height = 300;
+
+  mjsMaterial* material = mjs_addMaterial(spec, 0);
+  mjs_setString(material->name, "floor");
+  mjs_setInStringVec(material->textures, mjTEXROLE_RGB, "checker");
+
+  mjsGeom* floor = mjs_addGeom(mjs_findBody(spec, "world"), 0);
+  mjs_setString(floor->material, "floor");
+  floor->type = mjGEOM_PLANE;
+  floor->size[0] = 1;
+  floor->size[1] = 1;
+  floor->size[2] = 0.01;
+  mjs_setString(floor->material, "floor");
+
+  mjModel* model = mj_compile(spec, 0);
+  EXPECT_THAT(model, NotNull());
+
+  mj_deleteModel(model);
+  mj_deleteSpec(spec);
+}
+
 }  // namespace
 }  // namespace mujoco