Homebrew 3DS Homebrew App Framerate control

[Peanut42]

Hi to everybody!

I managed to get an a copy of Cubic Ninja, installed the exploit and install everything. I started to program a game. The game already exists, is written in SDL, I understand that is not the same, but, I managed to copy images and do everything "like" SDL.

Now I have a strange problem, I can't control the velolicty of the game. I'm searching for examples in Internet and most games don't do frame control. If someone knows how to "delay" each frame to something near 24 fps, it will be great.

I found some funcs: svcSleepThread, svcGetSystemTick, APT_SetAppCpuTimeLimit and osGetTime, but I don't know how exactly they can helpme. I've tried svcSleepThread and SetAppCpuTime, but no luck. I know that osGetTime can meassure the time, but how do I do "microsleeps" (something like SDL_Delay).

Thanks for reading.

By the way, the game source code is at Github (https://github.com/gatuno/PaddlePuffle3DS/blob/master/source/main.c)

 

[elhobbs]

Hi to everybody!

I managed to get an a copy of Cubic Ninja, installed the exploit and install everything. I started to program a game. The game already exists, is written in SDL, I understand that is not the same, but, I managed to copy images and do everything "like" SDL.

Now I have a strange problem, I can't control the velolicty of the game. I'm searching for examples in Internet and most games don't do frame control. If someone knows how to "delay" each frame to something near 24 fps, it will be great.

I found some funcs: svcSleepThread, svcGetSystemTick, APT_SetAppCpuTimeLimit and osGetTime, but I don't know how exactly they can helpme. I've tried svcSleepThread and SetAppCpuTime, but no luck. I know that osGetTime can meassure the time, but how do I do "microsleeps" (something like SDL_Delay).

Thanks for reading.

By the way, the game source code is at Github (https://github.com/gatuno/PaddlePuffle3DS/blob/master/source/main.c)

Use svcSleepThread to sleep. Keep in mind it uses nanoseconds. You can measure ticks using svcGetSystemTick and take the difference from the last frame. If this value is smaller than your target frame time than sleep for the difference. 268123480/24 would be your target ticks per frame.

 

[Peanut42]

Thanks a lot!

I solved to something like (again) SDL:

/* Used 12 because with 24 still runs too fast! */
#define FPS (268123480/12)

void game_loop (void) {
    u64 last_time, now_time;
    while (aptMainLoop ()) {
        //Wait for VBlank
        gspWaitForVBlank();
       
        last_time = svcGetSystemTick ();
        /* Do your game loop here and swap buffers */
        now_time = svcGetSystemTick ();
        if (now_time < last_time + FPS) svcSleepThread (last_time + FPS - now_time);
    }
}

 

[elhobbs]

Thanks a lot!

I solved to something like (again) SDL:

/* Used 12 because with 24 still runs too fast! */
#define FPS (268123480/12)

void game_loop (void) {
    u64 last_time, now_time;
    while (aptMainLoop ()) {
        //Wait for VBlank
        gspWaitForVBlank();
      
        last_time = svcGetSystemTick ();
        /* Do your game loop here and swap buffers */
        now_time = svcGetSystemTick ();
        if (now_time < last_time + FPS) svcSleepThread (last_time + FPS - now_time);
    }
}

I would do something like this

#define TICKS_PER_FRAME (268123480/24)

void game_loop(void) {
   u64 last_time, now_time, u64 frame_time;
   
   last_time = svcGetSystemTick();
   
   while (aptMainLoop()) {

     /* Do your game loop here */
     
     //Wait for VBlank
     gspWaitForVBlank();
     gfxFlushBuffers();
     gfxSwapBuffers();

     now_time = svcGetSystemTick();
     frame_time = now_time - last_time;
     last_time = now_time;
     if (frame_time < TICKS_PER_FRAME) svcSleepThread(TICKS_PER_FRAME - frame_time);
   }
}

 

[nop90]

I would do something like this

#define TICKS_PER_FRAME (268123480/24)
..
     now_time = svcGetSystemTick();
     frame_time = now_time - last_time;
     last_time = now_time;
     if (frame_time < TICKS_PER_FRAME) svcSleepThread(TICKS_PER_FRAME - frame_time);
..

But is svcSleepThread parameter in ticks? Isn't it in nanosecond?

 

[TheCruel]

The reason you probably can't find frame control examples is because it's a backwards approach. Instead of trying to get a framerate that achieves the right velocity, you should be using the framerate in your velocity calculations. Example :

    while (aptMainLoop())
    {
        while (eventmanager.pollEvent(event)) {
            processEvent(event); // Process input to change just like player velocity
        }
        deltaTime = clock.restart(); // Get time elapse since last frame render

        update(deltaTime.asSeconds()); // Update positioning of everything
        render(); // Draw everything now that it's repositioned
    }

Then in your game code you just have an update() method like this one:
https://github.com/cpp3ds/cpp3ds-template/blob/master/src/main.cpp#L22

Then all you have to do is something like: player.setPosition(delta * player.velocity.x, delta * player.velocity.y);

Then will ensure consistent movement regardless of players experiencing 5 fps or 60. You just set your velocity to how many pixel per second you want something to move.

Now I'm not saying you should rewrite everything to follow this. Just letting you know for the future, because when you try to lock the framerate, then you introduce more problems (e.g. if there's a cpu intensive or laggy part in a game, it causes a slowdown instead of just dropping some frames of animation).