android: implement android backend

Author: jcelerier

.gitignore

@@ -93,3 +93,86 @@ build
 
 .vscode
 
+### Generated by gibo (https://github.com/simonwhitaker/gibo)
+### https://raw.github.com/github/gitignore/15d684578f37580886f29e4b8462f3a27f722cb5/Android.gitignore
+
+# Gradle files
+.gradle/
+build/
+
+# Local configuration file (sdk path, etc)
+local.properties
+
+# Log/OS Files
+*.log
+
+# Android Studio generated files and folders
+captures/
+.externalNativeBuild/
+.cxx/
+*.aab
+*.apk
+output-metadata.json
+
+# IntelliJ
+*.iml
+.idea/
+misc.xml
+deploymentTargetDropDown.xml
+render.experimental.xml
+
+# Keystore files
+*.jks
+*.keystore
+
+# Google Services (e.g. APIs or Firebase)
+google-services.json
+
+# Android Profiling
+*.hprof
+### Generated by gibo (https://github.com/simonwhitaker/gibo)
+### https://raw.github.com/github/gitignore/15d684578f37580886f29e4b8462f3a27f722cb5/Gradle.gitignore
+
+.gradle
+**/build/
+!**/src/**/build/
+
+# Ignore Gradle GUI config
+gradle-app.setting
+
+# Avoid ignoring Gradle wrapper jar file (.jar files are usually ignored)
+!gradle-wrapper.jar
+
+# Avoid ignore Gradle wrappper properties
+!gradle-wrapper.properties
+
+# Cache of project
+.gradletasknamecache
+
+# Eclipse Gradle plugin generated files
+# Eclipse Core
+.project
+# JDT-specific (Eclipse Java Development Tools)
+.classpath
+### Generated by gibo (https://github.com/simonwhitaker/gibo)
+### https://raw.github.com/github/gitignore/15d684578f37580886f29e4b8462f3a27f722cb5/CMake.gitignore
+
+CMakeLists.txt.user
+CMakeCache.txt
+CMakeFiles
+CMakeScripts
+Testing
+Makefile
+cmake_install.cmake
+install_manifest.txt
+compile_commands.json
+CTestTestfile.cmake
+_deps
+CMakeUserPresets.json
+
+# CLion
+#  JetBrains specific template is maintained in a separate JetBrains.gitignore that can
+#  be found at https://github.com/github/gitignore/blob/main/Global/JetBrains.gitignore
+#  and can be added to the global gitignore or merged into this file.  For a more nuclear
+#  option (not recommended) you can uncomment the following to ignore the entire idea folder.
+#cmake-build-*

CMakeLists.txt

@@ -35,6 +35,7 @@ option(LIBREMIDI_NO_JACK "Disable JACK back-end" OFF)
 option(LIBREMIDI_NO_PIPEWIRE "Disable PipeWire back-end" OFF)
 option(LIBREMIDI_NO_NETWORK "Disable Network back-end" OFF)
 option(LIBREMIDI_NO_KEYBOARD "Disable Computer keyboard back-end" OFF)
+cmake_dependent_option(LIBREMIDI_NO_ANDROID "Disable Android AMidi back-end" OFF "ANDROID" OFF)
 
 option(LIBREMIDI_NO_EXPORTS "Disable dynamic symbol exporting" OFF)
 option(LIBREMIDI_NO_BOOST "Do not use Boost if available" OFF)
@@ -70,6 +71,7 @@ include(libremidi.jack)
 include(libremidi.pipewire)
 include(libremidi.keyboard)
 include(libremidi.net)
+include(libremidi.android)
 
 ### Install ###
 include(libremidi.install)

cmake/libremidi.android.cmake

@@ -0,0 +1,18 @@
+### Android ###
+if(ANDROID AND NOT LIBREMIDI_NO_ANDROID)
+  # Check for AMidi API availability (API level 29+)
+  # Also we need API 31+ for JNI_GetCreatedJavaVMs
+  if(ANDROID_NATIVE_API_LEVEL AND ANDROID_NATIVE_API_LEVEL GREATER_EQUAL 31)
+    message(STATUS "libremidi: Using Android AMidi API")
+    message(STATUS "       !!! Remember to include MidiDeviceCallback.java in your Android app")
+    message(STATUS "       !!! See the example in examples/android/java/dev/celtera/libremidi")
+
+    target_compile_definitions(libremidi ${_public} LIBREMIDI_ANDROID=1)
+    target_link_libraries(libremidi ${_public} amidi log nativehelper)
+    target_sources(libremidi ${_public}
+      "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include/libremidi/backends/android/helpers.cpp>"
+    )
+  else()
+    message(FATAL_ERROR "libremidi: Android AMidi API requires API level 31+ (current: ${ANDROID_NATIVE_API_LEVEL})")
+  endif()
+endif()

include/libremidi/api-c.h

@@ -22,6 +22,7 @@ typedef enum libremidi_api
   PIPEWIRE,       /*!< PipeWire */
   KEYBOARD,       /*!< Computer keyboard input */
   NETWORK,        /*!< MIDI over IP */
+  ANDROID_AMIDI,  /*!< Android AMidi API */
 
   // MIDI 2.0 APIs
   ALSA_RAW_UMP = 0x1000, /*!< Raw ALSA API for MIDI 2.0 */

include/libremidi/api.hpp

@@ -64,6 +64,8 @@ inline constexpr libremidi::API default_api() noexcept
   return API::ALSA_SEQ;
 #elif defined(__emscripten__)
   return API::EMSCRIPTEN_WEBMIDI;
+#elif defined(LIBREMIDI_ANDROID)
+  return API::ANDROID_AMIDI;
 #else
   return API::DUMMY;
 #endif

include/libremidi/backends.hpp

@@ -71,6 +71,10 @@
   #include <libremidi/backends/network_ump.hpp>
 #endif
 
+#if defined(LIBREMIDI_ANDROID)
+  #include <libremidi/backends/android/android.hpp>
+#endif
+
 namespace libremidi
 {
 // The order here will control the order of the API search in
@@ -124,6 +128,10 @@ static constexpr auto available_backends = make_tl(
 #if defined(LIBREMIDI_NETWORK)
     ,
     net::backend{}
+#endif
+#if defined(LIBREMIDI_ANDROID)
+    ,
+    android::backend{}
 #endif
     ,
     dummy_backend{});

include/libremidi/backends/android/android.hpp

@@ -0,0 +1,33 @@
+#pragma once
+#include <libremidi/backends/android/config.hpp>
+#include <libremidi/backends/android/midi_in.hpp>
+#include <libremidi/backends/android/midi_out.hpp>
+#include <libremidi/backends/android/observer.hpp>
+
+namespace libremidi
+{
+namespace android
+{
+struct backend
+{
+  using midi_in = android::midi_in;
+  using midi_out = android::midi_out;
+  using midi_observer = android::observer;
+  using midi_in_configuration = android::input_configuration;
+  using midi_out_configuration = android::output_configuration;
+  using midi_observer_configuration = android::observer_configuration;
+  static const constexpr auto API = libremidi::API::ANDROID_AMIDI;
+  static const constexpr std::string_view name = "android";
+  static const constexpr std::string_view display_name = "Android MIDI API";
+
+  static bool available() noexcept
+  {
+#if defined(__ANDROID__)
+    return true;
+#else
+    return false;
+#endif
+  }
+};
+}
+}

include/libremidi/backends/android/config.hpp

@@ -0,0 +1,23 @@
+#pragma once
+#include <libremidi/config.hpp>
+
+namespace libremidi
+{
+namespace android
+{
+struct input_configuration
+{
+  std::string_view client_name = "libremidi client";
+};
+
+struct output_configuration
+{
+  std::string_view client_name = "libremidi client";
+};
+
+struct observer_configuration
+{
+  std::string_view client_name = "libremidi client";
+};
+}
+}