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need some help please *beginer*

 
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cruisx



Joined: 25 Mar 2008
Posts: 8
PostPosted: Wed Apr 02, 2008 8:08 am    Post subject: need some help please *beginer* Reply with quote
ok i need some help guys. I am trying to lean how to do collision detection with 2 objects on the screen but i am kinda stuck, im sure the problem is an easy one, but for a beginner i am having some trouble.

Code:
//Oslib header file
#include <oslib/oslib.h>

//This is needed for eboot
PSP_MODULE_INFO("OSLib Sample", 0, 1, 1);
PSP_MAIN_THREAD_ATTR(THREAD_ATTR_USER | THREAD_ATTR_VFPU);

//this creates pointers for our images.
OSL_IMAGE *sprite, *sprite2, *sprite3;

//definations
#define DOWN 0
#define UP 35
#define RIGHT 70
#define LEFT 105

//variables
int sprite_position;
int sprite_march;

//declare the function like buttons and spriteAnimation
void Buttons();
void SpriteAnimate();
int collision(OSL_IMAGE *img1,float img1posX, float img1posY, OSL_IMAGE *img2, float img2posX, float img2posY,OSL_IMAGE *img3, float img3posX, float img3posY );

int main()
{

//start the Oslib library
   oslInit(0);
//start the graphixs mode
   oslInitGfx(OSL_PF_8888, 1);

//sets the transparency color
   oslSetTransparentColor(RGB(255,0,255));

//loads the images into memory
   sprite = oslLoadImageFile("sprite.png", OSL_IN_RAM, OSL_PF_5551);
   sprite2 = oslLoadImageFile("sprite2.png", OSL_IN_RAM, OSL_PF_5551);
   sprite3 = oslLoadImageFile("sprite3.png", OSL_IN_RAM, OSL_PF_5551);

//Disables the transparent color so it cannot be used again
   oslDisableTransparentColor();

//sees if all files are avaiable
   if (!sprite || !sprite2||!sprite3)
      oslDebug("! one or more of the files were missing, the program cannot run");
      
      
//Sets the sprites original position, lets see if i can get 2 sprites on da bloody screen
   sprite->x = 155;
   sprite->y = 95;
   sprite_position = DOWN;

//sets second sprite position
   sprite2->x = 230;
   sprite2->y = 130;
   
//sets thrid sprite pos
   sprite3->x = 270;
   sprite3->y = 130;


//main while loop
   while (!osl_quit)
   {
      //to be able ot draw on the screen
         oslStartDrawing();
         
      //Buttons
         Buttons();
         
      //draws a green background
         oslDrawGradientRect(0,0,480,272,RGB(0,128,0),RGB(0,128,0), RGB(128,255,128), RGB(128,255,128));
         
      //this draws the images to the screen
         oslDrawImage(sprite);
         oslDrawImage(sprite2);
         oslDrawImage(sprite3);
         
      //stops the drawing mode
         oslEndDrawing();
         
      //sync the screen
         oslSyncFrame();
      }
      
      //terminate the program
      oslEndGfx();
      oslQuit();
      return 0;
   }
   
      void Buttons()
      {
      //starts up the psp buttons
         oslReadKeys();
         
      if (osl_keys->held.down)
      {
         if(!collision(sprite, sprite->x, sprite->y + 2, sprite2, sprite2->x, sprite2->y, sprite3, sprite3->x, sprite3->y ))
         {
         //sprite movement
         sprite->y +=2;
         
         //sets sprite position on sprite sheet
            sprite_position = DOWN;
         
         //calls sprie animate
            SpriteAnimate();
      }
      }
            
         if (osl_keys->held.up)
      {
         if(!collision(sprite, sprite->x, sprite->y - 2, sprite2, sprite2->x, sprite2->y,sprite3, sprite3->x, sprite3->y ))
         {
            sprite->y-= 2;
            sprite_position = UP;
            SpriteAnimate();
         
      }
      }
      
      if (osl_keys->held.right)
    {
         if(!collision(sprite, sprite->x + 2, sprite->y, sprite2, sprite2->x, sprite2->y,sprite3, sprite3->x, sprite3->y  ))
         {
        sprite->x += 2;
        sprite_position = RIGHT;
        SpriteAnimate();
    }
   }
         
              if (osl_keys->held.left)
    {
      if(!collision(sprite, sprite->x - 2, sprite->y, sprite2, sprite2->x, sprite2->y,sprite3, sprite3->x, sprite3->y  ))
      {
        sprite->x -= 2;
        sprite_position = LEFT;
        SpriteAnimate();
    }
   }
         
            //If a button is not pressed
    if (!osl_keys->held.value)
    {
    //Start the variable over for when a button is pressed again
        sprite_march = 0;

        //Sets the sprite's direction
        oslSetImageTileSize(sprite,0,sprite_position,22,35);
    }
}


void SpriteAnimate()
   {   
        //Moves the sprite in the row that it is in
        sprite_march++;

        //Moves the sprite constantly
        oslSetImageTileSize(sprite,(sprite_march * 22),sprite_position,22,35);

        //resets the sprite movement in that row
        if (sprite_march == 6) sprite_march = 0;
   
}
         
      
      int collision(OSL_IMAGE *img1,float img1posX, float img1posY, OSL_IMAGE *img2, float img2posX, float img2posY, OSL_IMAGE *img3, float img3posX, float img3posY )
{
   int collision;
   collision = 0;
   float img1width  = img1->stretchX;
   float img1height = img1->stretchY;
   float img2width  = img2->stretchX;
   float img2height = img2->stretchY;
   float img3width = img3->stretchX;
   float img3height = img3->stretchY;
 
   
   if ((img1posX + img1width > img2posX) &&
       (img1posX < img2posX + img2width) &&
      (img1posX + img1width > img3posX) &&
       (img1posX < img2posX + img3width) &&
       (img1posY + img1height > img2posY) &&
       (img1posY < img2posY + img2height) )
{
         collision = 1;               
   }     
   return collision;
}


I know where the problem is but i dont know what im doing wrong


Code:
if ((img1posX + img1width > img2posX) &&
       (img1posX < img2posX + img2width) &&
     [B] (img1posX + img1width > img3posX) &&
       (img1posX < img2posX + img3width) &&[/B]
       (img1posY + img1height > img2posY) &&
       (img1posY < img2posY + img2height) )
{



if i put that in, none of the sprites have collision but if i take out the Bolded parts the first sprite has collision but the second one dose not.(second sprite as in the second object, not the character that is moving). How do i modify this correctly for every new object on the screen? help will be greatly appreciated.
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jean



Joined: 05 Jan 2008
Posts: 489
PostPosted: Wed Apr 02, 2008 7:03 pm    Post subject: Reply with quote
Just a few hints:
1) Collision is to be performed between two entities at a time.
2) Collision is generally not a commutative task because speed and acceleration are taken into account *BUT* In your case it's simple and commutative, so be sure not to check the same two times.
3) Write a single function that checks if a point is inside a shape and reuse it everytime you need to.

i.e.
Code:

for each shape
   for each vertex of current shape
        check if the vertex is inside any other shape
              if so, append a "collision detected between a and b" flag into a list

  parse the list and for each collision detected, act accordingly
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PosX100



Joined: 15 Aug 2007
Posts: 98
PostPosted: Wed Apr 02, 2008 9:33 pm    Post subject: Reply with quote
So , you're not making a tile-based game?

Well , then , search on google how to perform bounding box collision.

Its really easy.


The calculation is simple , you just need to check if x1,x1+w1,y1,y1+h1 ,
x2,x2+w2,y2,y2+h2 collide....

w=width
h=height
x=x position
y=y position


In games , bounding box collision usually used before performing any other type collision(eg :pixel/and any other complex collision formula) to save up cpu , but for a very simple game(like a shooter for example) it should be enough..


[EDIT]
Hey, wait..you already have a collision detection function in your code

Code:

    int collision(OSL_IMAGE *img1,float img1posX, float img1posY, OSL_IMAGE *img2, float img2posX, float img2posY, OSL_IMAGE *img3, float img3posX, float img3posY )


But you're doing a big mistake.

Why you're checking 3 objects?
You should check 2 objects at a time.

So , this should be enough:
Code:

int collision(OSL_IMAGE *img1,float img1posX, float img1posY, OSL_IMAGE *img2, float img2posX, float img2posY)
{
  //Its better to use a pointer to the actual struct/class member variable..
  //you can also use pointer reference for the images...
   float * img1width  = &img1->stretchX,img1height = &img1->stretchY,
   img2width  = &img2->stretchX,img2height = &img2->stretchY;

   return ((img1posX + img1width > img2posX) &&
       (img1posX < img2posX + img2width) &&
       (img1posY + img1height > img2posY) &&
       (img1posY < img2posY + img2height) ));
}
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cruisx



Joined: 25 Mar 2008
Posts: 8
PostPosted: Thu Apr 03, 2008 7:32 am    Post subject: Reply with quote
PosX100 wrote:
So , you're not making a tile-based game?

Well , then , search on google how to perform bounding box collision.

Its really easy.


The calculation is simple , you just need to check if x1,x1+w1,y1,y1+h1 ,
x2,x2+w2,y2,y2+h2 collide....

w=width
h=height
x=x position
y=y position


In games , bounding box collision usually used before performing any other type collision(eg :pixel/and any other complex collision formula) to save up cpu , but for a very simple game(like a shooter for example) it should be enough..


[EDIT]
Hey, wait..you already have a collision detection function in your code

Code:

    int collision(OSL_IMAGE *img1,float img1posX, float img1posY, OSL_IMAGE *img2, float img2posX, float img2posY, OSL_IMAGE *img3, float img3posX, float img3posY )


But you're doing a big mistake.

Why you're checking 3 objects?
You should check 2 objects at a time.

So , this should be enough:
Code:

int collision(OSL_IMAGE *img1,float img1posX, float img1posY, OSL_IMAGE *img2, float img2posX, float img2posY)
{
  //Its better to use a pointer to the actual struct/class member variable..
  //you can also use pointer reference for the images...
   float * img1width  = &img1->stretchX,img1height = &img1->stretchY,
   img2width  = &img2->stretchX,img2height = &img2->stretchY;

   return ((img1posX + img1width > img2posX) &&
       (img1posX < img2posX + img2width) &&
       (img1posY + img1height > img2posY) &&
       (img1posY < img2posY + img2height) ));
}


oh i did that for the second image becasue the first image is the moving sprite is it not? and also what part of my code should i replace with yours? Thanks once again though =) ill llook into the box collision
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