midi 2 conversion: fix midi2 to midi1, add an example

fixes #160

Author: jcelerier

cmake/libremidi.examples.cmake

@@ -17,6 +17,7 @@ add_example(midiobserve)
 add_example(echo)
 add_example(cmidiin)
 add_example(cmidiin2)
+add_example(midi1_to_midi2)
 add_example(midiclock_in)
 add_example(midiclock_out)
 add_example(midiout)

examples/midi1_to_midi2.cpp

@@ -0,0 +1,39 @@
+#include "utils.hpp"
+
+#include <libremidi/backends.hpp>
+#include <libremidi/libremidi.hpp>
+
+#include <iostream>
+
+/**
+ * This example shows upscale of a MIDI 1 API into MIDI 2 messages
+ */
+
+int main()
+try
+{
+  // The observer object enumerates available inputs and outputs
+  // jack is a MIDI 1 API (there's also jack_ump which leverages the newer
+  // JACK / PipeWire MIDI 2 support).
+  libremidi::observer obs{{}, libremidi::jack_observer_configuration{}};
+  auto pi = obs.get_input_ports();
+  auto po = obs.get_output_ports();
+  if (pi.empty() || po.empty())
+    throw std::runtime_error("No MIDI in / out pair available");
+
+  // Create a midi in
+  auto on_ump = [&](const libremidi::ump& message) { std::cerr << message << "\n"; };
+  libremidi::midi_in midiin{{.on_message = on_ump}, libremidi::jack_input_configuration{}};
+
+  if (auto err = midiin.open_port(pi[0]); err != stdx::error{})
+    err.throw_exception();
+
+  // Wait until we exit
+  char input;
+  std::cin.get(input);
+}
+catch (const std::exception& error)
+{
+  std::cerr << error.what() << std::endl;
+  return EXIT_FAILURE;
+}

include/libremidi/detail/conversion.hpp

@@ -210,6 +210,7 @@ struct midi1_to_midi2
     switch (cmidi2_convert_midi1_to_ump(&context))
     {
       case CMIDI2_CONVERSION_RESULT_OK: {
+        // FIXME handle sysex here
         if (auto n = context.ump_proceeded_bytes; n > 0)
           return on_ump(context.ump, context.ump_proceeded_bytes / 4, timestamp);
         else

include/libremidi/midi_in.cpp

@@ -41,12 +41,11 @@ convert_midi2_to_midi1_input_configuration(const ump_input_configuration& base_c
     converter.convert(
         msg.bytes.data(), msg.bytes.size(), msg.timestamp,
         [cb](const uint32_t* ump, std::size_t n, int64_t ts) {
-      if(n >= 4)
-      {
-        libremidi::ump u{ump[0],ump[1],ump[2],ump[3]};
-        u.timestamp = ts;
-        cb(std::move(u));
-      }
+      libremidi::ump u{ump[0]};
+      for (std::size_t i = 1; i < n && i < 4; i++)
+        u.data[i] = ump[i];
+      u.timestamp = ts;
+      cb(std::move(u));
       return stdx::error{};
     });
   };