author Holmes Futrell Fri, 15 Aug 2008 00:40:47 +0000 branch gsoc2008_iphone changeset 2424 ecc18fbfdec3 parent 2423 74d25e48d54d child 2425 491958a6c881
Added references to SDL_IPHONE_MAX_GFORCE ... that way this value can change without altering the demos behavior. More understandable too.
1.1 --- a/XCodeiPhoneOS/Demos/src/accelerometer.c	Fri Aug 15 00:38:49 2008 +0000
1.2 +++ b/XCodeiPhoneOS/Demos/src/accelerometer.c	Fri Aug 15 00:40:47 2008 +0000
1.3 @@ -11,7 +11,12 @@
1.4  #define MILLESECONDS_PER_FRAME 16	/* about 60 frames per second */
1.5  #define DAMPING 0.5f;				/* after bouncing off a wall, damping coefficient determines final speed */
1.6  #define FRICTION 0.0008f			/* coefficient of acceleration that opposes direction of motion */
1.7 -#define GRAVITY_CONSTANT 0.02f		/* how sensitive the ship is to the accelerometer */
1.8 +#define GRAVITY_CONSTANT 0.004f		/* how sensitive the ship is to the accelerometer */
1.9 +
1.10 +/*	If we aren't on an iPhone, then this definition ought to yield reasonable behavior */
1.11 +#ifndef SDL_IPHONE_MAX_GFORCE
1.12 +#define SDL_IPHONE_MAX_GFORCE 5.0f
1.13 +#endif
1.15  static SDL_Joystick *accelerometer; /* used for controlling the ship */
1.17 @@ -26,20 +31,25 @@
1.19  void render(void) {
1.21 +
1.22  	/* get joystick (accelerometer) axis values and normalize them */
1.23 -	float amax = (float)(0x7FFF); /* largest Sint16 number */
1.24 -	float ax = SDL_JoystickGetAxis(accelerometer, 0) / amax;
1.25 -	float ay = -SDL_JoystickGetAxis(accelerometer, 1) / amax;
1.26 +	float ax = SDL_JoystickGetAxis(accelerometer, 0);
1.27 +	float ay = -SDL_JoystickGetAxis(accelerometer, 1);
1.29  	/* ship screen constraints */
1.30  	Uint32 minx = 0.0f;
1.31  	Uint32 maxx = SCREEN_WIDTH - ship.rect.w;
1.32  	Uint32 miny = 0.0f;
1.33  	Uint32 maxy = SCREEN_HEIGHT - ship.rect.h;
1.34 -
1.35 -	/* update velocity from accelerometer */
1.36 -	ship.vx += ax * GRAVITY_CONSTANT * MILLESECONDS_PER_FRAME;
1.37 -	ship.vy += ay * GRAVITY_CONSTANT * MILLESECONDS_PER_FRAME;
1.38 +
1.39 +#define SINT16_MAX ((float)(0x7FFF))
1.40 +
1.41 +	/* update velocity from accelerometer
1.42 +	   the factor SDL_IPHONE_MAX_G_FORCE / SINT16_MAX converts between
1.43 +	   SDL's units reported from the joytick, and units of g-force, as reported by the accelerometer
1.44 +	*/
1.45 +	ship.vx += ax * SDL_IPHONE_MAX_GFORCE / SINT16_MAX * GRAVITY_CONSTANT * MILLESECONDS_PER_FRAME;
1.46 +	ship.vy += ay * SDL_IPHONE_MAX_GFORCE / SINT16_MAX * GRAVITY_CONSTANT * MILLESECONDS_PER_FRAME;
1.48  	float speed = sqrt(ship.vx * ship.vx + ship.vy * ship.vy);