IntersectRect()

I want to use the WinAPI function IntersectRect() for collision detection in my game so can anyone tell me how to go about using this function.

i have to imaes loaded and two rects set to the exact position and size as the images and i want to be able to tell if they collide and if they do i want to havethe xpos of image1 be reduced by 100.

Code:

#include "cozSprite.h"
#include <windows.h>
cozSprite spaceship; //sets up object of class cozSprite
SDL_Surface *screen;
 class image1
{
 public:
  int width;
  int height;
  int xpos;
  int ypos;

  }image1;

class image2
{
 public:
  int width;
  int height;
  int xpos;
  int ypos;
}image2;

int main(int argc, char *argv[])
{
  Uint8* keys;
  /*-----------------------------------------------------------------*/
  // image1
  image1.width  = 201;
  image1.height = 199;
  image1.xpos   = 0;
  image1.ypos   = 0;

  // image2
  image2.width  = 201;
  image2.height = 201;
  image2.xpos  = 600;
  image2.ypos  = 0;

 /*-----------------------------------------------------------------*/
  if ( SDL_Init(SDL_INIT_AUDIO|SDL_INIT_VIDEO) < 0 ) {
    printf("Unable to init SDL: %s\n", SDL_GetError());
    exit(1); }
  atexit(SDL_Quit);

  screen=SDL_SetVideoMode(640,480,32,SDL_HWSURFACE|SDL_DOUBLEBUF);
  if ( screen == NULL ) {
    printf("Unable to set 640x480 video: %s\n", SDL_GetError());
    exit(1); }


    spaceship.Init(screen,202,201,2); //initializes the sprite
    spaceship.Load("space.bmp", 0,0,0); //loads the sprite
    spaceship.Load("space.bmp", 1,0,199);

  int done=0;

  while(done == 0)
  {
    SDL_Event event;

    while ( SDL_PollEvent(&event) )
    {
      if ( event.type == SDL_QUIT )  {  done = 1;  }

      if ( event.type == SDL_KEYDOWN )
      {
        if ( event.key.keysym.sym == SDLK_ESCAPE ) { done = 1; }
      }
    }
      RECT rect1;
      rect1.left   = image1.xpos;
      rect1.top    = image1.xpos + image1.width;
      rect1.right  = image1.xpos - image1.width;
      rect1.bottom = image1.ypos - image1.height;

      RECT rect2;
      rect2.left   = image2.xpos;
      rect2.top    = image2.xpos + image2.width;
      rect2.right  = image2.xpos - image2.width;
      rect2.bottom = image2.ypos - image2.height;


      keys = SDL_GetKeyState(NULL);
    if ( keys[SDLK_UP] ) { image1.ypos -= 1; }
    if ( keys[SDLK_DOWN] ) { image1.ypos += 1; }
    if ( keys[SDLK_LEFT] ) { image1.xpos -= 1; }
    if ( keys[SDLK_RIGHT] ) { image1.xpos += 1; }

     spaceship.Draw(0,image1.xpos,image1.ypos); //draws frame in specified postion on the screen
     spaceship.Draw(1,image2.xpos,image2.ypos);

     SDL_Flip(screen);




    }



  return 0;
}

please don't make any comments on the code i jsut threw this tegether but don't know how to use the function o am asking about. Do i need a third RECT?

Yes, you'll need a 3rd rect. The 3rd rect will represent the result of an intersection, if it returns TRUE.

Here's a basic example.

Code:

RECT rcOne, rcTwo, rcTemp;
SetRect(&rcOne,0,0,32,32);
SetRect(&rcTwo,10,10,42,42);
if(IntersectRect(&rcTemp,&rcOne,&rcTwo))
{
   MessageBox(NULL,"They intersect","...",NULL);
}
else
{
   MessageBox(NULL,"They don't intersect","...",NULL);
}

Depending on your particular needs the temp RECT could just be used in the check or if you need pixel-perfect collision detection then you could use the size and location of the temp RECT to get pixel data from that part of the two sprites.

Thanks