Writing Midi Out under macOS SDL2

SDL Development
1

My first post here was a question about whether it’s possible to write an SDL2 program to write midi commands to a midi output port under macOS . I wanted to add some text to this question saying that I succeeded a bit and then the whole message went into the orcus due to an editing error that occured to me. So I’m starting over from the point I have reached now:

I asked AI to write a little app under macOS and SDL2 that writes out a midi note (which I then can use as a basis for further development) Goal is to read Midi-OX logfiles and write the Midi Codes in there to the Midi Outputport (using the correct timestamp that’s in the log file).
This is what I got (based on macports rtmidi and SDL2):

seq.cpp:

#include <SDL2/SDL.h>  // Header path often varies slightly by system
#include <rtmidi/RtMidi.h>
#include 
#include 

int main(int argc, char* argv
) {
// 1. Initialize MIDI Output
RtMidiOut *midiout = new RtMidiOut();
if (midiout->getPortCount() == 0) {
std::cerr << “No MIDI ports available!” << std::endl;
delete midiout;
return 1;
}
midiout->openPort(0); // Open first available MIDI port

// 2. Initialize SDL2
if (SDL_Init(SDL_INIT_VIDEO) < 0) return -1;
SDL_Window* window = SDL_CreateWindow("MIDI Sequencer", 100, 100, 640, 480, SDL_WINDOW_SHOWN);
SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, 0);

bool running = true;
SDL_Event event;
std::vector<unsigned char> message;

while (running) {
    while (SDL_PollEvent(&event)) {
        if (event.type == SDL_QUIT) running = false;

        // Example: Press 'Space' to send a MIDI Note On
        if (event.type == SDL_KEYDOWN && event.key.keysym.sym == SDLK_SPACE) {
            message.clear();
            message.push_back(144); // Note On (Channel 1)
            message.push_back(60);  // Middle C
            message.push_back(90);  // Velocity
            midiout->sendMessage(&message);
            std::cout << "Sent: Note On (C3)" << std::endl;
        }
    }

    SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
    SDL_RenderClear(renderer);
    SDL_RenderPresent(renderer);
}

// Cleanup
delete midiout;
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
return 0;

}

Makefile:

# Compiler Settings
CXX      := clang++
CXXFLAGS := -std=c++17 -Wall -Wextra -D__MACOSX_CORE__
TARGET   := midi_app

# MacPorts Paths
MACPORTS_PATH := /opt/local
INCLUDES      := -I$(MACPORTS_PATH)/include
LDFLAGS       := -L$(MACPORTS_PATH)/lib

# Libraries
# SDL2 und RtMidi requirements macOS System-Frameworks
LIBS := -lSDL2 -lrtmidi \
        -framework CoreMIDI \
        -framework CoreAudio \
        -framework CoreFoundation \
        -framework AudioToolbox \
        -framework AudioUnit

# Source Files
SRCS := seq.cpp
OBJS := $(SRCS:.cpp=.o)

# Standard Target
all: $(TARGET)

$(TARGET): $(OBJS)
    $(CXX) $(OBJS) -o $(TARGET) $(LDFLAGS) $(LIBS)

%.o: %.cpp
    $(CXX) $(CXXFLAGS) $(INCLUDES) -c $< -o $@

# Misc
clean:
    rm -f $(OBJS) $(TARGET)

run: all
    ./$(TARGET)

.PHONY: all clean run

I succeeded with the above code and added a slight modification, to find out which output port it was suitable to write to.

#include <SDL2/SDL.h>  // Header path often varies slightly by system
#include <rtmidi/RtMidi.h>
#include <vector>
#include <iostream>


int main(int argc, char* argv[]) {
    int port_count=0;
// 1. Initialize MIDI Output
    RtMidiOut *midiout = new RtMidiOut();
    if ((port_count=midiout->getPortCount()) == 0) {
        std::cerr << "No MIDI ports available!" << std::endl;
        delete midiout;
        return 1;
    }
    std::cout << "# of ports: " << port_count << std::endl;
    for(int i=0;i<port_count;i++) {
       std::cout << midiout->getPortName(i) << std::endl;
    }
    midiout->openPort(1); // Open first available MIDI port

    // 2. Initialize SDL2
    if (SDL_Init(SDL_INIT_VIDEO) < 0) return -1;
    SDL_Window* window = SDL_CreateWindow("MIDI Sequencer", 100, 100, 640, 480, SDL_WINDOW_SHOWN);
    SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, 0);

    bool running = true;
    SDL_Event event;
    std::vector<unsigned char> message;

    while (running) {
        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_QUIT) running = false;

            // Example: Press 'Space' to send a MIDI Note On
            if (event.type == SDL_KEYDOWN && event.key.keysym.sym == SDLK_SPACE) {
                message.clear();
                message.push_back(144); // Note On (Channel 1)
                message.push_back(60);  // Middle C
                message.push_back(90);  // Velocity
                midiout->sendMessage(&message);
                std::cout << "Sent: Note On (C3)" << std::endl;
            }
        }

        SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
        SDL_RenderClear(renderer);
        SDL_RenderPresent(renderer);
    }

    // Cleanup
    delete midiout;
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    SDL_Quit();
    return 0;
}

Just wanted to share. No more questions. Thank you.