做點小改動，結果小球運動的時候出現難看的“軌跡”
不知道如何修改才能正常
int game(int argc ,char* argv[])
{
//Create a SDL screen.
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
ScreenSurface screen(SCREEN_WIDTH, SCREEN_HEIGHT);
//Fill background with white.(default is black)
screen.fillColor(0xFF, 0xFF, 0xFF);

//Load a sprite pic, and colorkey.(default color: R=0,G=0xFF,B=0xFF)
DisplaySurface sprite("dots.png", screen);
sprite.colorKey();

//the 4 dots's coordinate.
int atX[4] = {0, 590, 0, 590};
int atY[4] = {0, 0, 430, 430};
//the 4 dots's clip coordinate.
int fromX[4] = {0, 270, 0 ,270};
int fromY[4] = {0, 0, 190, 190};
//mouse's coordinate.
int px = 0;
int py = 0;
//dots's size.
const int IMG_WIDTH = 50;
const int IMG_HEIGHT = 50;
//clip dots.
for ( int i = 0; i < 4; i++ )
sprite.blit(atX[i], atY[i], fromX[i], fromY[i], IMG_WIDTH, IMG_HEIGHT);
//Draw dots and screen.
screen.flip();

//press ESC or click X to quit.
bool gameOver = false;
SDL_Event gameEvent;
while( gameOver == false ){
while ( SDL_PollEvent(&gameEvent) != 0 ){
if ( gameEvent.type == SDL_QUIT ){
gameOver = true;
}
if ( gameEvent.type == SDL_KEYUP ){
if ( gameEvent.key.keysym.sym == SDLK_ESCAPE ){
gameOver = true;
}
}
//mouse event
if ( gameEvent.type == SDL_MOUSEMOTION ) {
px = gameEvent.motion.x;
py = gameEvent.motion.y;
}
}
for(int i = 0 ; i < 4 ;i++)
{
if ( atX[i] < px )
atX[i]++;
if ( atX[i] > px )
atX[i]--;
if ( atY[i] < py )
atY[i]++;
if ( atY[i] > py )
atY[i]--;
}
//clip dots.
for ( int i = 0; i < 4; i++ )
sprite.blit(atX[i], atY[i], fromX[i], fromY[i], IMG_WIDTH, IMG_HEIGHT,2,2);
//Draw dots and screen.
screen.flip();
}

return 0;
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