title: 
aliases: 
tags:
  - cpp
category: 方法
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url: 
creation-time: 2024-02-04 20:03
modification-time: 2024-02-04 20:13:44

由于之前使用 MMSystem 库对手柄的数据进行读取 [[2023-10-17]] 的方式，在笔记本上接手柄总是出现一些虚拟手柄占用接口的问题（未找到原因）。另外找一种读取手柄数据的方式。
简单介绍一下使用 [[SDL]] 库读取手柄摇杆的方法。主要参考的源码是^[1]。

初始化手柄子系统

bool init() {
  // Initialization flag
  bool success = true;

  // Initialize SDL
  if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_JOYSTICK) < 0) {  // 源码里为了可视化手柄数值，进行了箭头绘制，所以额外初始化了一个video子系统
    printf("SDL could not initialize! SDL Error: %s\n", SDL_GetError());
    success = false;
  } else {
    // Set texture filtering to linear
    if (!SDL_SetHint(SDL_HINT_RENDER_SCALE_QUALITY, "1")) {
      printf("Warning: Linear texture filtering not enabled!");
    }

    // Check for joysticks
    if (SDL_NumJoysticks() < 1) {
      printf("Warning: No joysticks connected!\n");
    } else {
      // Load joystick
      gGameController = SDL_JoystickOpen(0);
      if (gGameController == NULL) {
        printf("Warning: Unable to open game controller! SDL Error: %s\n",
               SDL_GetError());
      }
    }
  }

  return success;
}

手柄关闭子系统

void close() {
  // Close game controller
  SDL_JoystickClose(gGameController);
  gGameController = NULL;

  // Quit SDL subsystems
  SDL_Quit();
}

主程序

int WinMain(int argc, char* args[]) {
  // Start up SDL and create window
  if (!init()) {
    printf("Failed to initialize!\n");
  } else {
    bool quit = false;

    // Event handler
    SDL_Event e;

    // Normalized direction
    int xDir = 0;
    int yDir = 0;

    // While application is running
    while (!quit) {
      // Handle events on queue
      while (SDL_PollEvent(&e) != 0) {
        // User requests quit
        if (e.type == SDL_QUIT) {
          quit = true;
        } else if (e.type == SDL_JOYAXISMOTION) {
          // Motion on controller 0
          if (e.jaxis.which == 0) {
            std::cout<<"e.jaxis.axis: "<<e.jaxis.axis<<std::endl;
            // X axis motion
            if (e.jaxis.axis == 0) {
              // Left of dead zone
              if (e.jaxis.value < -JOYSTICK_DEAD_ZONE) {
                xDir = e.jaxis.value;
              }
              // Right of dead zone
              else if (e.jaxis.value > JOYSTICK_DEAD_ZONE) {
                xDir = e.jaxis.value;
              } else {
                xDir = 0;
              }
            }
            // Y axis motion
            else if (e.jaxis.axis == 1) {
              // Below of dead zone
              if (e.jaxis.value < -JOYSTICK_DEAD_ZONE) {
                yDir = e.jaxis.value;
              }
              // Above of dead zone
              else if (e.jaxis.value > JOYSTICK_DEAD_ZONE) {
                yDir = e.jaxis.value;
              } else {
                yDir = 0;
              }
            }
          }
        }
      }

      // Calculate angle
      double joystickAngle = atan2((double)yDir, (double)xDir) * (180.0 / M_PI);
      std::cout << "yDire: " << yDir << " xDir: " << xDir << std::endl;
      // Correct angle
      if (xDir == 0 && yDir == 0) {
        joystickAngle = 0;
      }
    }
  }

  // Free resources and close SDL
  close();

  return 0;
}

关键的逻辑是，通过一个事件 SDL_Event 来表示摇杆是否运动，如果摇杆发生了运动，通过 axis 这个属性判断是 x 还是 y 方向的运动，然后保存到相应的摇杆位置状态值中。

Reference