SDL示例-控制球的移动[转载]

　//通过控制键盘来移动球




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#if defined(_MSC_VER)
＃i nclude "SDL.h"
#else
＃i nclude "SDL/SDL.h"
#endif

// Screen surface
SDL_Surface *gScreen;

// Screen pitch
#define PITCH (gScreen->pitch / 4)
// Screen width
#define WIDTH 480
// Screen height
#define HEIGHT 320
// Color of player's ball
#define BALLCOLOR 0x007fff
// Radius of the player's ball
#define RADIUS 12
// Background color
#define BGCOLOR 0x5f0000
// Wall color
#define WALLCOLOR 0x9f1f1f
// Definition of PI
#define PI 3.1415926535897932384626433832795f

// Player's thrust value
#define THRUST 0.1f
// Slowdown due to friction, etc.
#define SLOWDOWN 0.99f


// Player's position
float gXPos;
float gYPos;

// Player's motion vector
float gXMov;
float gYMov;

// Player's key status
int gKeyLeft;
int gKeyRight;
int gKeyUp;
int gKeyDown;


void drawcircle(int x, int y, int r, int c)
{
int i, j;
for (i = 0; i < 2 * r; i++)
{
// vertical clipping: (top and bottom)
if ((y - r + i) >= 0 && (y - r + i) < HEIGHT)
{
int len = (int)sqrt((float)(r * r - (r - i) * (r - i))) * 2;
int xofs = x - len / 2;

// left border
if (xofs < 0)
{
len += xofs;
xofs = 0;
}

// right border
if (xofs + len >= WIDTH)
{
len -= (xofs + len) - WIDTH;
}
int ofs = (y - r + i) * PITCH + xofs;
// note that len may be 0 at this point,
// and no pixels get drawn!
for (j = 0; j < len; j++)
((unsigned int*)gScreen->pixels)[ofs + j] = c;
}
}
}


void drawrect(int x, int y, int width, int height, int c)
{
int i, j;
for (i = 0; i < height; i++)
{
// vertical clipping: (top and bottom)
if ((y + i) >= 0 && (y + i) < HEIGHT)
{
int len = width;
int xofs = x;

// left border
if (xofs < 0)
{
len += xofs;
xofs = 0;
}

// right border
if (xofs + len >= WIDTH)
{
len -= (xofs + len) - WIDTH;
}
int ofs = (i + y) * PITCH + xofs;

// note that len may be 0 at this point,
// and no pixels get drawn!
for (j = 0; j < len; j++)
((unsigned int*)gScreen->pixels)[ofs + j] = c;
}
}
}


void init()
{
gXPos = WIDTH / 2;
gYPos = HEIGHT / 2;

gXMov = 0;
gYMov = 0;

gKeyLeft = 0;
gKeyRight = 0;
gKeyUp = 0;
gKeyDown = 0;
}


void render()
{
// Ask SDL for the time in milliseconds
int tick = SDL_GetTicks();
if (gKeyLeft) gXMov -= THRUST;
if (gKeyRight) gXMov += THRUST;
if (gKeyUp) gYMov -= THRUST;
if (gKeyDown) gYMov += THRUST;

gXMov *= SLOWDOWN;
gYMov *= SLOWDOWN;

gXPos += gXMov;
gYPos += gYMov;

// Lock surface if needed
if (SDL_MUSTLOCK(gScreen))
if (SDL_LockSurface(gScreen) < 0)
return;

// fill background
drawrect(0, 0, WIDTH, HEIGHT, BGCOLOR);
// draw borders
drawrect(0, 0, WIDTH, 8, WALLCOLOR);
drawrect(0, 0, 8, HEIGHT, WALLCOLOR);
drawrect(WIDTH - 8, 0, 8, HEIGHT, WALLCOLOR);
drawrect(0, HEIGHT - 8, WIDTH, 8, WALLCOLOR);

// draw the player object
drawcircle((int)gXPos,
(int)gYPos,
RADIUS,
BALLCOLOR);
// Unlock if needed
if (SDL_MUSTLOCK(gScreen))
SDL_UnlockSurface(gScreen);

// Tell SDL to update the whole gScreen
SDL_UpdateRect(gScreen, 0, 0, WIDTH, HEIGHT);
}


// Entry point
int main(int argc, char *argv[])
{
// Initialize SDL's subsystems - in this case, only video.
if (SDL_Init(SDL_INIT_VIDEO) < 0)
{
fprintf(stderr, "Unable to init SDL: %s\n", SDL_GetError());
exit(1);
}

// Register SDL_Quit to be called at exit; makes sure things are
// cleaned up when we quit.
atexit(SDL_Quit);
// Attempt to create a WIDTHxHEIGHT window with 32bit pixels.
gScreen = SDL_SetVideoMode(WIDTH, HEIGHT, 32, SDL_SWSURFACE);
init();

// If we fail, return error.
if (gScreen == NULL)
{
fprintf(stderr, "Unable to set up video: %s\n", SDL_GetError());
exit(1);
}

// Main loop: loop forever.
while (1)
{
// Render stuff
render();

// Poll for events, and handle the ones we care about.
SDL_Event event;
while (SDL_PollEvent(&event))
{
switch (event.type)
{
case SDL_KEYDOWN:
switch (event.key.keysym.sym)
{
case SDLK_LEFT:
gKeyLeft = 1;
break;
case SDLK_RIGHT:
gKeyRight = 1;
break;
case SDLK_UP:
gKeyUp = 1;
break;
case SDLK_DOWN:
gKeyDown = 1;
break;
}
break;
case SDL_KEYUP:
switch (event.key.keysym.sym)
{
case SDLK_ESCAPE:
// If escape is pressed, return (and thus, quit)
return 0;
case SDLK_LEFT:
gKeyLeft = 0;
break;
case SDLK_RIGHT:
gKeyRight = 0;
break;
case SDLK_UP:
gKeyUp = 0;
break;
case SDLK_DOWN:
gKeyDown = 0;
break;
}
break;
case SDL_QUIT:
return(0);
}
}
}
return 0;
}