accelerometer.c
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/*
* 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
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render(SDL_Renderer *renderer, int w, int h)
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{
/* get joystick (accelerometer) axis values and normalize them */
float ax = SDL_JoystickGetAxis(accelerometer, 0);
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float ay = SDL_JoystickGetAxis(accelerometer, 1);
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/* ship screen constraints */
Uint32 minx = 0.0f;
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Uint32 maxx = w - shipData.rect.w;
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Uint32 miny = 0.0f;
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Uint32 maxy = h - shipData.rect.h;
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#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 */
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Sint32 delay; /* time to pause waiting to draw next frame */
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int done; /* should we clean up and exit? */
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/* 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 |
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SDL_WINDOW_FULLSCREEN);
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renderer = SDL_CreateRenderer(window, 0, 0);
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SDL_GetWindowSize(window, &w, &h);
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/* 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 */
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shipData.x = (w - shipData.rect.w) / 2;
shipData.y = (h - shipData.rect.h) / 2;
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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;
}
}
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render(renderer, w, h);
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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;
}