From 8c36e6d95f48b6915ac0b2fdc7fb7302a76f4e64 Mon Sep 17 00:00:00 2001
From: Alexey Pelykh <alexey.pelykh@gmail.com>
Date: Wed, 28 Jul 2021 18:58:41 +0200
Subject: [PATCH] MaterialKey: expose constrainMaterial to Android (#4398)

---
 .../src/main/cpp/MaterialKey.cpp              | 36 ++++++++++++++++---
 .../filament/gltfio/MaterialProvider.java     | 18 ++++++++++
 2 files changed, 49 insertions(+), 5 deletions(-)

diff --git a/android/gltfio-android/src/main/cpp/MaterialKey.cpp b/android/gltfio-android/src/main/cpp/MaterialKey.cpp
index d3c63d36e0..554368fb7a 100644
--- a/android/gltfio-android/src/main/cpp/MaterialKey.cpp
+++ b/android/gltfio-android/src/main/cpp/MaterialKey.cpp
@@ -69,11 +69,6 @@ void MaterialKeyHelper::init(JNIEnv* env) {
     hasIOR = field("hasIOR", "Z");
 }
 
-extern "C" JNIEXPORT void JNICALL
-Java_com_google_android_filament_gltfio_MaterialProvider_00024MaterialKey_nGlobalInit(JNIEnv* env, jclass) {
-    MaterialKeyHelper::get().init(env);
-}
-
 void MaterialKeyHelper::copy(JNIEnv* env, MaterialKey& dst, jobject src) {
     dst.doubleSided = env->GetBooleanField(src, doubleSided);
     dst.unlit = env->GetBooleanField(src, unlit);
@@ -149,3 +144,34 @@ void MaterialKeyHelper::copy(JNIEnv* env, jobject dst, const MaterialKey& src) {
     env->SetBooleanField(dst, hasSheen, src.hasSheen);
     env->SetBooleanField(dst, hasIOR, src.hasIOR);
 }
+
+extern "C" JNIEXPORT void JNICALL
+Java_com_google_android_filament_gltfio_MaterialProvider_00024MaterialKey_nGlobalInit(JNIEnv* env, jclass) {
+    MaterialKeyHelper::get().init(env);
+}
+
+extern "C"
+JNIEXPORT void JNICALL
+Java_com_google_android_filament_gltfio_MaterialProvider_00024MaterialKey_nConstrainMaterial(JNIEnv* env, jclass,
+        jobject materialKey, jintArray uvMap) {
+    MaterialKey nativeMaterialKey = {};
+
+    auto& helper = MaterialKeyHelper::get();
+    helper.copy(env, nativeMaterialKey, materialKey);
+
+    UvMap nativeUvMap = {};
+    constrainMaterial(&nativeMaterialKey, &nativeUvMap);
+
+    // Copy the UvMap results from the native array into the JVM array.
+    jint* elements = env->GetIntArrayElements(uvMap, nullptr);
+    if (elements) {
+        const size_t javaSize = env->GetArrayLength(uvMap);
+        for (int i = 0, n = std::min(javaSize, nativeUvMap.size()); i < n; ++i) {
+            elements[i] = nativeUvMap[i];
+        }
+        env->ReleaseIntArrayElements(uvMap, elements, 0);
+    }
+
+    // The config parameter is an in-out parameter so we need to copy the results back to Java.
+    helper.copy(env, materialKey, nativeMaterialKey);
+}
diff --git a/android/gltfio-android/src/main/java/com/google/android/filament/gltfio/MaterialProvider.java b/android/gltfio-android/src/main/java/com/google/android/filament/gltfio/MaterialProvider.java
index 8da62c8e26..92557a6625 100644
--- a/android/gltfio-android/src/main/java/com/google/android/filament/gltfio/MaterialProvider.java
+++ b/android/gltfio-android/src/main/java/com/google/android/filament/gltfio/MaterialProvider.java
@@ -71,7 +71,25 @@ public interface MaterialProvider {
         static {
             nGlobalInit();
         }
+
+        /**
+         * Populate UV map according to the material key, altering latter if required.
+         *
+         * Filament supports up to 2 UV sets. glTF has arbitrary texcoord set indices, but it
+         * allows implementations to support only 2 simultaneous sets. Here we build a mapping
+         * table with 1-based indices where 0 means unused. Note that the order in which we drop
+         * textures can affect the look of certain assets. This "order of degradation" is
+         * stipulated by the glTF 2.0 specification.
+         *
+         * @param uvmap Output argument that gets populated with a small table that maps from a
+         *              glTF uv index to a Filament uv index (0 = UNUSED, 1 = UV0, 2 = UV1).
+         */
+        public void constrainMaterial(@NonNull @Size(min = 8) int[] uvmap) {
+            nConstrainMaterial(this, uvmap);
+        }
+
         private static native void nGlobalInit();
+        private static native void nConstrainMaterial(MaterialKey materialKey, int[] uvmap);
     };
 
     /**