/*

* 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

/* 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 *

shipData.vy +=

ay * SDL_IPHONE_MAX_GFORCE / SINT16_MAX * GRAVITY_CONSTANT *

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 */

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 */

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) {

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;

}