Mercurial > sdl-ios-xcode
changeset 2424:ecc18fbfdec3 gsoc2008_iphone
Added references to SDL_IPHONE_MAX_GFORCE ... that way this value can change without altering the demos behavior. More understandable too.
| author | Holmes Futrell <hfutrell@umail.ucsb.edu> |
|---|---|
| date | Fri, 15 Aug 2008 00:40:47 +0000 |
| parents | 74d25e48d54d |
| children | 491958a6c881 |
| files | XCodeiPhoneOS/Demos/src/accelerometer.c |
| diffstat | 1 files changed, 18 insertions(+), 8 deletions(-) [+] |
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--- a/XCodeiPhoneOS/Demos/src/accelerometer.c Fri Aug 15 00:38:49 2008 +0000 +++ b/XCodeiPhoneOS/Demos/src/accelerometer.c Fri Aug 15 00:40:47 2008 +0000 @@ -11,7 +11,12 @@ #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 0.02f /* how sensitive the ship is to the accelerometer */ +#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 */ @@ -26,20 +31,25 @@ void render(void) { + /* get joystick (accelerometer) axis values and normalize them */ - float amax = (float)(0x7FFF); /* largest Sint16 number */ - float ax = SDL_JoystickGetAxis(accelerometer, 0) / amax; - float ay = -SDL_JoystickGetAxis(accelerometer, 1) / amax; + float ax = SDL_JoystickGetAxis(accelerometer, 0); + float ay = -SDL_JoystickGetAxis(accelerometer, 1); /* ship screen constraints */ Uint32 minx = 0.0f; Uint32 maxx = SCREEN_WIDTH - ship.rect.w; Uint32 miny = 0.0f; Uint32 maxy = SCREEN_HEIGHT - ship.rect.h; - - /* update velocity from accelerometer */ - ship.vx += ax * GRAVITY_CONSTANT * MILLESECONDS_PER_FRAME; - ship.vy += ay * GRAVITY_CONSTANT * MILLESECONDS_PER_FRAME; + +#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 + */ + ship.vx += ax * SDL_IPHONE_MAX_GFORCE / SINT16_MAX * GRAVITY_CONSTANT * MILLESECONDS_PER_FRAME; + ship.vy += ay * SDL_IPHONE_MAX_GFORCE / SINT16_MAX * GRAVITY_CONSTANT * MILLESECONDS_PER_FRAME; float speed = sqrt(ship.vx * ship.vx + ship.vy * ship.vy);