Add texture attribute to lights.

PiperOrigin-RevId: 763739805
Change-Id: I333ed2ac68f30f79f688ca01d7b5fd6bf2d836c9

test/user/user_objects_test.cc

@@ -2294,6 +2294,29 @@ TEST_F(UserObjectsTest, FrameTransformsLight) {
   mj_deleteModel(m);
 }
 
+TEST_F(ContentTypeTest, ImageLightsReferenceTexture) {
+  static constexpr char xml[] = R"(
+  <mujoco>
+    <asset>
+      <texture name="texture" type="cube" builtin="flat" mark="cross" width="8"
+       rgb1="0.8 0.6 0.4" rgb2="0.8 0.6 0.4" markrgb="1 1 1"/>
+    </asset>
+
+    <worldbody>
+      <light type="image" texture="texture"/>
+    </worldbody>
+  </mujoco>
+  )";
+
+  std::array<char, 1024> error;
+  mjModel* m = LoadModelFromString(xml, error.data(), error.size());
+  EXPECT_THAT(m, NotNull());
+  EXPECT_EQ(m->ntex, 1);
+  EXPECT_EQ(m->nlight, 1);
+  EXPECT_THAT(m->light_texid[0], 0);
+  mj_deleteModel(m);
+}
+
 
 // ------------- test bvh ------------------------------------------------------
 TEST_F(UserObjectsTest, RobustBVH) {

test/xml/testdata/lights.xml

@@ -0,0 +1,12 @@
+<mujoco>
+  <asset>
+    <texture name="texture1" type="2d" file="hfield.png"/>
+  </asset>
+  <worldbody>
+    <light name="light1" type="spot" pos="1 2 3" dir="0 0 1" diffuse="0.1 0.2 0.3" ambient="0.4 0.5 0.6" specular="0.7 0.8 0.95"/>
+    <light name="light2" type="spot" attenuation="0.1 0.2 0.3" cutoff="0.4" exponent="0.5"/>
+    <light name="light3" type="point" range="2" intensity="300" bulbradius="0.5"/>
+    <light name="light4" type="directional" dir="1 0 0" active="false" castshadow="false"/>
+    <light name="light5" type="image" texture="texture1"/>
+  </worldbody>
+</mujoco>