blob: 3b7985faa098b707e3de1e1bf25b7b93806b3d78 [file] [log] [blame]
 /* * accelerometer.c * written by Holmes Futrell * use however you want */ #include "SDL.h" #include "math.h" #include "common.h" #define MILLESECONDS_PER_FRAME 16 /* about 60 frames per second */ #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) { /* 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 * MILLESECONDS_PER_FRAME; shipData.vy += ay * SDL_IPHONE_MAX_GFORCE / SINT16_MAX * GRAVITY_CONSTANT * MILLESECONDS_PER_FRAME; float 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 * MILLESECONDS_PER_FRAME > 0) { /* apply friction */ shipData.vx -= dirx * FRICTION * MILLESECONDS_PER_FRAME; shipData.vy -= diry * FRICTION * MILLESECONDS_PER_FRAME; } 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 * MILLESECONDS_PER_FRAME; shipData.y += shipData.vy * MILLESECONDS_PER_FRAME; 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; Uint32 startFrame; /* time frame began to process */ Uint32 endFrame; /* time frame ended processing */ Sint32 delay; /* time to pause waiting to draw next frame */ 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, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_OPENGL | SDL_WINDOW_FULLSCREEN); renderer = SDL_CreateRenderer(window, 0, 0); SDL_GetWindowSize(window, &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) { startFrame = SDL_GetTicks(); SDL_Event event; while (SDL_PollEvent(&event)) { if (event.type == SDL_QUIT) { done = 1; } } render(renderer, w, h); endFrame = SDL_GetTicks(); /* figure out how much time we have left, and then sleep */ delay = MILLESECONDS_PER_FRAME - (endFrame - startFrame); if (delay < 0) { delay = 0; } else if (delay > MILLESECONDS_PER_FRAME) { delay = MILLESECONDS_PER_FRAME; } SDL_Delay(delay); } /* delete textures */ SDL_DestroyTexture(ship); SDL_DestroyTexture(space); /* shutdown SDL */ SDL_Quit(); return 0; }