sdl

accelerometer.c (6878B)

---

 /*
  *  accelerometer.c
  *  written by Holmes Futrell
  *  use however you want
  */
 
 #include "SDL.h"
 #include <math.h>
 #include "common.h"
 
 #define DAMPING 0.5f;           /* after bouncing off a wall, damping coefficient determines final speed */
 #define FRICTION 0.0008f        /* coefficient of acceleration that opposes direction of motion */
 #define GRAVITY_CONSTANT 0.004f /* how sensitive the ship is to the accelerometer */
 
 /*  If we aren't on an iPhone, then this definition ought to yield reasonable behavior */
 #ifndef SDL_IPHONE_MAX_GFORCE
 #define SDL_IPHONE_MAX_GFORCE 5.0f
 #endif
 
 static SDL_Joystick *accelerometer;     /* used for controlling the ship */
 
 static struct
 {
     float x, y;                 /* position of ship */
     float vx, vy;               /* velocity of ship (in pixels per millesecond) */
     SDL_Rect rect;              /* (drawn) position and size of ship */
 } shipData;
 
 static SDL_Texture *ship = 0;        /* texture for spaceship */
 static SDL_Texture *space = 0;       /* texture for space (background */
 
 void
 render(SDL_Renderer *renderer, int w, int h, double deltaTime)
 {
     double deltaMilliseconds = deltaTime * 1000;
     float speed;
 
     /* get joystick (accelerometer) axis values and normalize them */
     float ax = SDL_JoystickGetAxis(accelerometer, 0);
     float ay = SDL_JoystickGetAxis(accelerometer, 1);
 
     /* ship screen constraints */
     Uint32 minx = 0.0f;
     Uint32 maxx = w - shipData.rect.w;
     Uint32 miny = 0.0f;
     Uint32 maxy = h - shipData.rect.h;
 
 #define SINT16_MAX ((float)(0x7FFF))
 
     /* update velocity from accelerometer
        the factor SDL_IPHONE_MAX_G_FORCE / SINT16_MAX converts between
        SDL's units reported from the joytick, and units of g-force, as reported by the accelerometer
      */
     shipData.vx +=
         ax * SDL_IPHONE_MAX_GFORCE / SINT16_MAX * GRAVITY_CONSTANT *
         deltaMilliseconds;
     shipData.vy +=
         ay * SDL_IPHONE_MAX_GFORCE / SINT16_MAX * GRAVITY_CONSTANT *
         deltaMilliseconds;
 
     speed = sqrt(shipData.vx * shipData.vx + shipData.vy * shipData.vy);
 
     if (speed > 0) {
         /* compensate for friction */
         float dirx = shipData.vx / speed;   /* normalized x velocity */
         float diry = shipData.vy / speed;   /* normalized y velocity */
 
         /* update velocity due to friction */
         if (speed - FRICTION * deltaMilliseconds > 0) {
             /* apply friction */
             shipData.vx -= dirx * FRICTION * deltaMilliseconds;
             shipData.vy -= diry * FRICTION * deltaMilliseconds;
         } else {
             /* applying friction would MORE than stop the ship, so just stop the ship */
             shipData.vx = 0.0f;
             shipData.vy = 0.0f;
         }
     }
 
     /* update ship location */
     shipData.x += shipData.vx * deltaMilliseconds;
     shipData.y += shipData.vy * deltaMilliseconds;
 
     if (shipData.x > maxx) {
         shipData.x = maxx;
         shipData.vx = -shipData.vx * DAMPING;
     } else if (shipData.x < minx) {
         shipData.x = minx;
         shipData.vx = -shipData.vx * DAMPING;
     }
     if (shipData.y > maxy) {
         shipData.y = maxy;
         shipData.vy = -shipData.vy * DAMPING;
     } else if (shipData.y < miny) {
         shipData.y = miny;
         shipData.vy = -shipData.vy * DAMPING;
     }
 
     /* draw the background */
     SDL_RenderCopy(renderer, space, NULL, NULL);
 
     /* draw the ship */
     shipData.rect.x = shipData.x;
     shipData.rect.y = shipData.y;
 
     SDL_RenderCopy(renderer, ship, NULL, &shipData.rect);
 
     /* update screen */
     SDL_RenderPresent(renderer);
 
 }
 
 void
 initializeTextures(SDL_Renderer *renderer)
 {
 
     SDL_Surface *bmp_surface;
 
     /* load the ship */
     bmp_surface = SDL_LoadBMP("ship.bmp");
     if (bmp_surface == NULL) {
         fatalError("could not ship.bmp");
     }
     /* set blue to transparent on the ship */
     SDL_SetColorKey(bmp_surface, 1,
                     SDL_MapRGB(bmp_surface->format, 0, 0, 255));
 
     /* create ship texture from surface */
     ship = SDL_CreateTextureFromSurface(renderer, bmp_surface);
     if (ship == 0) {
         fatalError("could not create ship texture");
     }
     SDL_SetTextureBlendMode(ship, SDL_BLENDMODE_BLEND);
 
     /* set the width and height of the ship from the surface dimensions */
     shipData.rect.w = bmp_surface->w;
     shipData.rect.h = bmp_surface->h;
 
     SDL_FreeSurface(bmp_surface);
 
     /* load the space background */
     bmp_surface = SDL_LoadBMP("space.bmp");
     if (bmp_surface == NULL) {
         fatalError("could not load space.bmp");
     }
     /* create space texture from surface */
     space = SDL_CreateTextureFromSurface(renderer, bmp_surface);
     if (space == 0) {
         fatalError("could not create space texture");
     }
     SDL_FreeSurface(bmp_surface);
 
 }
 
 
 
 int
 main(int argc, char *argv[])
 {
 
     SDL_Window *window;         /* main window */
     SDL_Renderer *renderer;
     int done;                   /* should we clean up and exit? */
     int w, h;
 
     /* initialize SDL */
     if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_JOYSTICK) < 0) {
         fatalError("Could not initialize SDL");
     }
 
     /* create main window and renderer */
     window = SDL_CreateWindow(NULL, 0, 0, 320, 480, SDL_WINDOW_FULLSCREEN | SDL_WINDOW_ALLOW_HIGHDPI);
     renderer = SDL_CreateRenderer(window, 0, 0);
     
     SDL_GetWindowSize(window, &w, &h);
     SDL_RenderSetLogicalSize(renderer, w, h);
 
     /* print out some info about joysticks and try to open accelerometer for use */
     printf("There are %d joysticks available\n", SDL_NumJoysticks());
     printf("Default joystick (index 0) is %s\n", SDL_JoystickName(0));
     accelerometer = SDL_JoystickOpen(0);
     if (accelerometer == NULL) {
         fatalError("Could not open joystick (accelerometer)");
     }
     printf("joystick number of axis = %d\n",
            SDL_JoystickNumAxes(accelerometer));
     printf("joystick number of hats = %d\n",
            SDL_JoystickNumHats(accelerometer));
     printf("joystick number of balls = %d\n",
            SDL_JoystickNumBalls(accelerometer));
     printf("joystick number of buttons = %d\n",
            SDL_JoystickNumButtons(accelerometer));
 
     /* load graphics */
     initializeTextures(renderer);
 
     /* setup ship */
     shipData.x = (w - shipData.rect.w) / 2;
     shipData.y = (h - shipData.rect.h) / 2;
     shipData.vx = 0.0f;
     shipData.vy = 0.0f;
 
     done = 0;
     /* enter main loop */
     while (!done) {
         double deltaTime = updateDeltaTime();
         SDL_Event event;
         while (SDL_PollEvent(&event)) {
             if (event.type == SDL_QUIT) {
                 done = 1;
             }
         }
         render(renderer, w, h, deltaTime);
         SDL_Delay(1);
     }
 
     /* delete textures */
     SDL_DestroyTexture(ship);
     SDL_DestroyTexture(space);
 
     /* shutdown SDL */
     SDL_Quit();
 
     return 0;
 
 }