Any demo to use SDL3 on qt for android？

[Mangomm]

Currently, I am developing Android-based software using Qt. Since I used SDL for the Windows project before, I also wanted to use SDL for audio playback on Android. However, I found that by simply adding the header files and linking the libraries as usual, it was impossible to call SDL. For example, when I called SDL_Init(flags), it failed and printed an error message: "Application did not initialize properly. Did you include SDL_main.h in the file containing your main() function?" Could you please tell me how to call SDL in Qt Creator? This problem is really bothering me now, and I believe many people have the same issue! If you want my test project, I can send it to you.

[icculus]

I'm not aware of an example, but SDL wants to do some pretty complex startup stuff on Android. It wants to be launched from a little piece of Java code that sets up some things and calls into the C library for further setup before calling your main() function. It also wants to call back and forth between that Java code and C as necessary to talk to various Android system APIs.

You can't just drop SDL into an Android app as a shared library that you call into, like you can on other platforms.

Now, there may be a way to make this work, but that's the immediate stumbling block you are likely hitting.

[Mangomm]

I'm not aware of an example, but SDL wants to do some pretty complex startup stuff on Android. It wants to be launched from a little piece of Java code that sets up some things and calls into the C library for further setup before calling your main() function. It also wants to call back and forth between that Java code and C as necessary to talk to various Android system APIs.

You can't just drop SDL into an Android app as a shared library that you call into, like you can on other platforms.

Now, there may be a way to make this work, but that's the immediate stumbling block you are likely hitting.

Is there a plan to turn this example into a sample and incorporate it into the SDL3 test cases?

[madebr]

I wouldn't mind adding a qt6 test case/example.
As a first step, please create and share a small c++ example that also runs on desktop and shows off the power of SDL3 in Qt.

[Mangomm]

Hello, today I found some time to modify the content of testffmpeg.c. I only made the changes for Windows. I used the Qt handle and D3D11 for zero-copy rendering.
Test project code address: https://github.com/Mangomm/test-sdl-hwnd;
Usage method: After downloading, place the corresponding dll file into the exe build directory of Qt. Click the "play" button to start playing. A new window will be generated for playback. The "stop" interface might have some issues, but it won't affect the "play" function.
This example is based on the earlier version reference (https://github.com/libsdl-org/SDL/blob/a842446f62dc0d00773d41b932f4649b6bd3da5f/test/testffmpeg.c). Please take a look and see if you need to update to the latest testffmpeg.c.

[Mangomm]

我不介意添加一个 Qt6 测试用例/示例。 作为第一步，请创建并分享一个能在桌面运行的小型 C++ 示例，以展示 Qt 中 SDL3 的强大功能。

Could you please see if it's possible to create a test case using a Qt project, which calls the SDL library to play videos and audio on the Android system based on this example?

[Mangomm]

Hello, today I found some time to modify the content of testffmpeg.c. I only made the changes for Windows. I used the Qt handle and D3D11 for zero-copy rendering. Test project code address: https://github.com/Mangomm/test-sdl-hwnd; Usage method: After downloading, place the corresponding dll file into the exe build directory of Qt. Click the "play" button to start playing. A new window will be generated for playback. The "stop" interface might have some issues, but it won't affect the "play" function. This example is based on the earlier version reference (https://github.com/libsdl-org/SDL/blob/a842446f62dc0d00773d41b932f4649b6bd3da5f/test/testffmpeg.c). Please take a look and see if you need to update to the latest testffmpeg.c.

You need to specify the path of the file you want to play. In the function void MainWindow::on_btn_clicked(),

[madebr]

Hello, today I found some time to modify the content of testffmpeg.c. I only made the changes for Windows. I used the Qt handle and D3D11 for zero-copy rendering. Test project code address: https://github.com/Mangomm/test-sdl-hwnd;

Thanks for the work. I have some remarks:

• I was hoping on a qt example without external dependencies (=ffmpeg): this makes it much easier (and fast) to test and build. (Making it as an optional dependency would be fine)
• If we want the example to become part of the SDL3 test suite, it should either reuse or refactor existing code to avoid duplicated code (and associated divergence/bit rot)
• The code does not build on qt6: QDesktopWidget is not available there
• The code does not build on Linux: #include <d3d11.h> fails

[Mangomm]

Hello, today I found some time to modify the content of testffmpeg.c. I only made the changes for Windows. I used the Qt handle and D3D11 for zero-copy rendering. Test project code address: https://github.com/Mangomm/test-sdl-hwnd;

Thanks for the work. I have some remarks:

• I was hoping on a qt example without external dependencies (=ffmpeg): this makes it much easier (and fast) to test and build. (Making it as an optional dependency would be fine)
• If we want the example to become part of the SDL3 test suite, it should either reuse or refactor existing code to avoid duplicated code (and associated divergence/bit rot)
• The code does not build on qt6: QDesktopWidget is not available there
• The code does not build on Linux: #include <d3d11.h> fails

OK, I spent some time debugging the SDL3 audio playback, supporting callback mode and queue mode. I have tested it on Windows and it works properly. You can use this example to make it compatible with Android, so as to show everyone how to use Qt to call SDL3 for Android development.

[Mangomm]

#include <SDL3/SDL.h>
#include <stdio.h>
#include <stdint.h>
#include <string.h>

#define PCM_FILE "44100_2_s16.pcm"

#define SAMPLE_RATE 44100
#define CHANNELS 2


struct AudioContext {
    FILE* fp;
};


void SDLCALL audio_callback(void* userdata, SDL_AudioStream* stream, int additional_amount, int total_amount)
{
    struct AudioContext* ctx = (struct AudioContext*)userdata;
    if (!ctx->fp)
        return;

    if (additional_amount > 0) {
        Uint8* data = SDL_stack_alloc(Uint8, additional_amount);
        memset(data, 0, additional_amount);
        if (data) {
            int read_bytes = fread(data, 1, additional_amount, ctx->fp);
            if (read_bytes > 0) {
                SDL_PutAudioStreamData(stream, data, additional_amount);
            }
        }
        SDL_stack_free(data);
    }

}

//---------------------------------------------
// test1：callback mode
//---------------------------------------------
void test1()
{
    printf("=== test1: callback mode (SDL3) ===\n");

    if (SDL_Init(SDL_INIT_AUDIO) < 0) {
        printf("SDL init failed\n");
        return;
    }

    FILE* fp = fopen(PCM_FILE, "rb");
    if (!fp) {
        printf("open pcm failed\n");
        return;
    }

    struct AudioContext ctx = { fp };

    SDL_AudioSpec spec = {};
    spec.freq = SAMPLE_RATE;
    spec.format = SDL_AUDIO_S16;
    spec.channels = CHANNELS;

    SDL_AudioStream* audio_stream = SDL_OpenAudioDeviceStream(SDL_AUDIO_DEVICE_DEFAULT_OUTPUT, &spec, audio_callback, &ctx);
    if (!audio_stream) {
        printf("SDL_OpenAudioDeviceStream failed!");
        return;
    }
    SDL_ResumeAudioDevice(SDL_GetAudioStreamDevice(audio_stream));

    printf("playing... press Enter to stop\n");
    getchar();

    SDL_DestroyAudioStream(audio_stream);
    fclose(fp);
    SDL_Quit();
}

static SDL_bool IsPlanarAudioFormat(int format)
{
    // SDL does not have a planar mode?
    return SDL_FALSE;
}

//---------------------------------------------
// test2：Queue mode
//---------------------------------------------
void test2()
{
    printf("=== test2: push mode (SDL3) ===\n");

    Uint8* data = NULL;
    // test 1024 nb_samples
    int nb_samples = 1024;
    // one frame size
    int frame_size;
    int read_bytes;

    if (SDL_Init(SDL_INIT_AUDIO) < 0) {
        printf("SDL init failed\n");
        return;
    }

    FILE* fp = fopen(PCM_FILE, "rb");
    if (!fp) {
        printf("open pcm failed\n");
        return;
    }

    SDL_AudioSpec spec = {};
    spec.freq = SAMPLE_RATE;
    spec.format = SDL_AUDIO_S16;
    spec.channels = CHANNELS;

    SDL_AudioStream* audio_stream = SDL_OpenAudioDeviceStream(SDL_AUDIO_DEVICE_DEFAULT_OUTPUT, &spec, NULL, NULL);
    if (!audio_stream) {
        printf("SDL_OpenAudioDeviceStream failed!");
        goto finished;
    }
    SDL_ResumeAudioDevice(SDL_GetAudioStreamDevice(audio_stream));


    frame_size = nb_samples * SDL_AUDIO_FRAMESIZE(spec);
    data = SDL_stack_alloc(Uint8, frame_size);
    if (!data) {
        printf("create data failed\n");
        goto finished;
    }

    while(1){

        read_bytes = fread(data, 1, frame_size, fp);
        if (read_bytes <= 0)
            break;


        SDL_SetAudioStreamFormat(audio_stream, &spec, NULL);

        if (CHANNELS > 1 && IsPlanarAudioFormat(0)) {
            //InterleaveAudio(p, frame, &spec);
        } else {
            SDL_PutAudioStreamData(audio_stream, data, frame_size);
        }

    }

    // 等待播放完成
    while (SDL_GetAudioStreamQueued(audio_stream) > 0) {
        SDL_Delay(100);
    }


    printf("play finished\n");

finished:

    SDL_DestroyAudioStream(audio_stream);
    if(fp){
        fclose(fp);
    }
    if(data){
        SDL_stack_free(data);
    }
    SDL_Quit();
}

//---------------------------------------------
// main
//---------------------------------------------
int main(int argc, char* argv[])
{
    if (argc < 2) {
        printf("usage: %s 1|2\n", argv[0]);
        return -1;
    }

    if (argv[1][0] == '1') {
        test1();
    } else {
        test2();
    }

    return 0;
}

[Mangomm]

Hello, will this Qt test case be updated in the next version?

[madebr]

@1bsyl With the current Android backend, what is actually possible with Qt on Android?
Reading the docs, Qt android app's activities need to subclass QtActivity which clashes with SDLActivity.

[slouken]

@1bsyl With the current Android backend, what is actually possible with Qt on Android? Reading the docs, Qt android app's activities need to subclass QtActivity which clashes with SDLActivity.

Steam Link uses both Qt and SDL, and it works by using SDL audio and controller support in the Qt activity and then switching to a separate SDL activity for graphics.

[madebr]

Does that mean SDLGPU is currently not usable on Android?

[slouken]

Does that mean SDLGPU is currently not usable on Android?

In general, or with Qt?

I'm not sure about with Qt, but it works fine in general as long as capable graphics drivers are available.

[1bsyl]

@madebr sorry, I've never used SDL with Qt on Android