Properly use SDK 26+ APIs (#9417)

With minSDK less than 26, it's unsafe to use APIs in nativewindow.h 
that appeared at API 26 or more, even when using the weak symbol
technique. This is because pre 26, libnativewindow.h didn't exist and
therefore the build system cannot link against it.

Currently Filament's minSdk is 21, which means we should never use
nativewindow.h API after 26.

In this PR we chose the strategy at compile time; either the more
modern weak symbol or the old way with dlsym based on __ANDROID_API__.

filament/backend/CMakeLists.txt

@@ -104,6 +104,7 @@ if (FILAMENT_SUPPORTS_OPENGL AND NOT FILAMENT_USE_EXTERNAL_GLES3)
         list(APPEND SRCS src/VirtualMachineEnv.cpp)
     endif ()
     if (ANDROID)
+        list(APPEND SRCS src/AndroidNdk.cpp)
         list(APPEND SRCS src/AndroidNativeWindow.cpp)
         list(APPEND SRCS src/AndroidSwapChainHelper.cpp)
         list(APPEND SRCS src/AndroidFrameCallback.cpp)

filament/backend/include/backend/platforms/PlatformEGLAndroid.h

@@ -19,6 +19,7 @@
 
 #include "AndroidSwapChainHelper.h"
 #include "AndroidFrameCallback.h"
+#include "AndroidNdk.h"
 
 #include <backend/AcquiredImage.h>
 #include <backend/DriverEnums.h>
@@ -46,7 +47,7 @@ class ExternalStreamManagerAndroid;
  * A concrete implementation of OpenGLPlatform and subclass of PlatformEGL that supports
  * EGL on Android. It adds Android streaming functionality to PlatformEGL.
  */
-class PlatformEGLAndroid : public PlatformEGL {
+class PlatformEGLAndroid : public PlatformEGL, public AndroidNdk {
 public:
 
     PlatformEGLAndroid() noexcept;

filament/backend/include/backend/platforms/VulkanPlatformAndroid.h

@@ -18,6 +18,7 @@
 #define TNT_FILAMENT_BACKEND_PLATFORMS_VULKAN_PLATFORM_ANDROID_H
 
 #include "AndroidFrameCallback.h"
+#include "AndroidNdk.h"
 
 #include <backend/DriverEnums.h>
 #include <backend/platforms/VulkanPlatform.h>
@@ -26,7 +27,7 @@
 
 namespace filament::backend {
 
-class VulkanPlatformAndroid : public VulkanPlatform {
+class VulkanPlatformAndroid : public VulkanPlatform, public AndroidNdk {
 public:
     ExternalImageHandle UTILS_PUBLIC createExternalImage(AHardwareBuffer const* buffer,
             bool sRGB) noexcept;

filament/backend/src/AndroidNativeWindow.cpp

@@ -16,6 +16,7 @@
 
 #include "AndroidNativeWindow.h"
 
+#include <android/api-level.h>
 #include <android/native_window.h>
 
 #include <utils/compiler.h>
@@ -30,11 +31,16 @@
 namespace filament::backend {
 
 std::pair<int, bool> NativeWindow::isValid(ANativeWindow* const anw) noexcept {
+#if __ANDROID_API__ >= 26
+    // libnativewindow.so is not available before API level 26, this means we can't call
+    // any method above 25 (even protected by __builtin_available()).
     if (__builtin_available(android 28, *)) {
         // this a proxy for is_valid()
         auto const result = ANativeWindow_getBuffersDataSpace(anw);
         return { result, result >= 0 };
     }
+#endif
+
     // fallback on using private APIs
     NativeWindow const* pWindow = reinterpret_cast<NativeWindow const*>(anw);
     if (UTILS_LIKELY(pWindow->query)) {
@@ -82,6 +88,10 @@ AndroidProducerThrottling::AndroidProducerThrottling() {
     // note: we don't need to dlclose() mNativeWindowLib here, because the library will be cleaned
     // when the process ends and dlopen() are ref-counted. dlclose() NDK documentation documents
     // not to call dlclose().
+
+    // libnativewindow.so is not available before API level 26, this means we can't call
+    // any method above 25 (even protected by __builtin_available()).
+
     void* nativeWindowLibHandle = dlopen("libnativewindow.so", RTLD_LOCAL | RTLD_NOW);
     if (nativeWindowLibHandle) {
         mSetProducerThrottlingEnabled =

filament/backend/src/AndroidNdk.cpp

@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2025 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "AndroidNdk.h"
+
+#include <android/hardware_buffer.h>
+
+#include <utils/compiler.h>
+
+#include <mutex>
+
+#include <dlfcn.h>
+
+namespace filament::backend {
+
+UTILS_UNUSED
+static std::once_flag sInitOnce{};
+
+template <typename T>
+UTILS_UNUSED
+static void loadSymbol(void* handle, const char* symbol, T& pfn) {
+    pfn = T(dlsym(handle, symbol));
+}
+
+#if FILAMENT_USE_DLSYM(26)
+AndroidNdk::Ndk AndroidNdk::ndk{};
+#endif
+
+AndroidNdk::AndroidNdk() {
+#if FILAMENT_USE_DLSYM(26)
+    std::call_once(sInitOnce, [] {
+        // note: we don't need to dlclose() mNativeWindowLib here, because the library will be cleaned
+        // when the process ends and dlopen() are ref-counted. dlclose() NDK documentation documents
+        // not to call dlclose().
+        if (__builtin_available(android 26, *)) {
+            void* h = dlopen("libnativewindow.so", RTLD_LOCAL | RTLD_NOW);
+            if (h) {
+                loadSymbol(h, "AHardwareBuffer_acquire", ndk.AHardwareBuffer_acquire);
+                loadSymbol(h, "AHardwareBuffer_release", ndk.AHardwareBuffer_release);
+                loadSymbol(h, "AHardwareBuffer_describe", ndk.AHardwareBuffer_describe);
+            }
+        }
+    });
+#endif
+}
+
+} // filament::backend

filament/backend/src/AndroidNdk.h

@@ -0,0 +1,79 @@
+/*
+ * Copyright (C) 2025 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FILAMENT_BACKEND_ANDROIDNDK_H
+#define FILAMENT_BACKEND_ANDROIDNDK_H
+
+#include <android/native_window.h>
+#include <android/hardware_buffer.h>
+
+#define FILAMENT_REQUIRES_API(x) __attribute__((__availability__(android,introduced=x)))
+
+#define FILAMENT_USE_DLSYM(api) (__ANDROID_API__ < (api))
+
+namespace filament::backend {
+
+class AndroidNdk {
+public:
+    AndroidNdk();
+
+#if FILAMENT_USE_DLSYM(26)
+
+    static void AHardwareBuffer_acquire(
+            AHardwareBuffer* buffer) FILAMENT_REQUIRES_API(26) {
+        ndk.AHardwareBuffer_acquire(buffer);
+    }
+
+    static void AHardwareBuffer_release(
+            AHardwareBuffer* buffer) FILAMENT_REQUIRES_API(26) {
+        ndk.AHardwareBuffer_release(buffer);
+    }
+
+    static void AHardwareBuffer_describe(
+            AHardwareBuffer const* buffer, AHardwareBuffer_Desc* desc) FILAMENT_REQUIRES_API(26) {
+        ndk.AHardwareBuffer_describe(buffer, desc);
+    }
+
+#else
+
+    static void AHardwareBuffer_acquire(
+            AHardwareBuffer* buffer) FILAMENT_REQUIRES_API(26) {
+        ::AHardwareBuffer_acquire(buffer);
+    }
+    static void AHardwareBuffer_release(
+            AHardwareBuffer* buffer) FILAMENT_REQUIRES_API(26) {
+        ::AHardwareBuffer_release(buffer);
+    }
+    static void AHardwareBuffer_describe(
+            AHardwareBuffer const* buffer, AHardwareBuffer_Desc* desc) FILAMENT_REQUIRES_API(26) {
+        ::AHardwareBuffer_describe(buffer, desc);
+    }
+
+#endif
+
+private:
+#if FILAMENT_USE_DLSYM(26)
+    static struct Ndk {
+        void (*AHardwareBuffer_acquire)(AHardwareBuffer*);
+        void (*AHardwareBuffer_release)(AHardwareBuffer*);
+        void (*AHardwareBuffer_describe)(AHardwareBuffer const*, AHardwareBuffer_Desc*);
+    } ndk;
+#endif
+};
+
+} // filament::backend
+
+#endif //FILAMENT_BACKEND_ANDROIDNDK_H