sample-page-curl: add comments to variables, etc.

android/samples/sample-page-curl/src/main/java/com/google/android/filament/pagecurl/Page.java

@@ -105,13 +105,13 @@ public class Page {
         final float e = 0.01f;
         final int count = this.positions.capacity() / 3;
 
-        float[] p = new float[3];
-        float[] p1 = new float[3];
-        float[] p2 = new float[3];
-        float[] du = new float[3];
-        float[] dv = new float[3];
-        float[] n = new float[3];
-        float[] q = new float[4];
+        float[] p = new float[3];  // position of the current vertex
+        float[] p1 = new float[3]; // position of neighboring vertex along the U axis
+        float[] p2 = new float[3]; // position of neighboring vertex along the V axis
+        float[] du = new float[3]; // tangent vector along the U axis
+        float[] dv = new float[3]; // tangent vector along the V axis
+        float[] n = new float[3];  // normal vector (du x dv)
+        float[] q = new float[4];  // quaternion for the tangent frame
 
         for (int i = 0; i < count; i++) {
             final float u = this.uvs.get(i * 2);

android/samples/sample-page-curl/src/main/java/com/google/android/filament/pagecurl/PageMaterials.java

@@ -46,7 +46,7 @@ public class PageMaterials {
     }
 
     public PageMaterials(Engine engine, AssetManager assets) {
-        ByteBuffer asset = readAsset(assets, "materials/lit.filamat");
+        ByteBuffer asset = readAsset(assets, "materials/curl.filamat");
         assert asset != null;
         mMaterial = new Material.Builder()
                 .payload(asset, asset.remaining())

android/samples/sample-page-curl/src/main/materials/curl.mat

@@ -1,5 +1,5 @@
 material {
-    name : lit,
+    name : curl,
     shadingModel : lit,
     doubleSided: true,
     parameters : [

android/samples/sample-page-curl/src/main/res/values/strings.xml

@@ -1,3 +1,3 @@
 <resources>
-  <string name="app_name">Lit Cube</string>
+  <string name="app_name">Page Curl</string>
 </resources>