Collision Detection

[CyberCarsten]

Hi all...

I'm prorgramming a breakout/paddle game and its comming together nicely, but now I have gotten to the Collision Detection(when the ball hits the blocks)...

I create objects(BOB's) using my engine which has a lot of wrapper functions, fx Collison_BOBS:

int Collision_BOBS(BOB_PTR bob1,     // Pointer to first BOB
                              BOB_PTR bob2);   // Pointer to second BOB 

The function returns TRUE is the two bounding rectangles overlap.

So i have tried to make for loop to check whenever the ball BOB hits the box[28] BOB, but my machine hanged....

I have also tried to do it manually like this

if(Collision_BOBS(&ball, &box[1])){
      ......
} 

etc.....

Hanged again....anyone have any ideas....my main game loop look like this:

int Game_Main(void *parms)
{

// check of user is trying to exit
if (KEY_DOWN(VK_ESCAPE))
    PostMessage(main_window_handle, WM_DESTROY,0,0);
if (KEY_DOWN(VK_LEFT)) {
    if (paddle.x >5) {
        paddle.x = paddle.x -10;
        Move_BOB(&paddle);
    }
} else if(KEY_DOWN(VK_RIGHT)) {
    if(paddle.x + paddle.width  < SCREEN_WIDTH) {
        paddle.x = paddle.x +10;
        Move_BOB(&paddle);
    }
}

// start the timing clock
Start_Clock();

// clear the drawing surface
DD_Fill_Surface(lpddsback, 0);

Draw_BOB(&paddle,lpddsback);
Draw_BOB(&ball,lpddsback);
for (int draw = 0; draw<28; draw++)
Draw_BOB(&box[draw],lpddsback);

ball.xv = xangle;
ball.yv = yangle;
Move_BOB(&ball);

//the ball has gone outside the screen
if(ball.x <= 0 | ball.x >= SCREEN_WIDTH - ball.width ){
    xangle = -xangle;
}
// the ball has gone outside the screen
if(ball.y <= 0 |ball.y == SCREEN_HEIGHT - ball.height){
    yangle = -yangle;
}
// the ball has hit the paddle
if(Collision_BOBS(&ball,&paddle)){
    yangle=-yangle; // change direction
}



// flip the surfaces
DD_Flip();


// sync to 30ish fps
Wait_Clock(30);

// return success
return(1);

} // end Game_Main 

please let me know if you need more source code...
Thanks in advance!

[Zaei]

box[28] doesnt exist. Remember, in C++, 28 elements go from 0..27.

Z.

[CyberCarsten]

oh typo...but it still doesn't do it right, because when I test for collision, the game might be testing block 5 and the has just hit block 20......thats my problem....

[Zaei]

You need to step through your code line by line, and find out EXACTLY where it crashes. From what I can see above, the problem may be in your Collision function.

Z.

[CyberCarsten]

The Collision function works just fine, but I was trying to step through the code using a loop but it didn't work because when the loop what testing block 5 I might hit block 26 with ball, and it also crashes.....any suggestions...

The loop I was using:

for(int counter; counter<27; counter++)
if(Collision_BOBS(&ball,&box[counter])){
......//Do whatever with the block
} 

[Zaei]

The collision function obviously does not work fine, as it crashes. How are you defining the box variable, also?

Z.

[CyberCarsten]

Like this:
BOB box[27];

[Zaei]

Change it to a 28. You attempt to access 27, which is one beyond the number that you have.

Z.

[CyberCarsten]

Now I have got the loop running without hanging, but the collision still isn't good...

#define LAST_HIT_RIGHT 1
#define LAST_HIT_LEFT 2
#define LAST_HIT_TOP 3
#define LAST_HIT_BOTTOM 4

int lasthit; 

for(int counter = 0; counter<28; counter++)
if(Collision_BOBS(&ball,&box[counter])){
    if(lasthit == LAST_HIT_LEFT){
        if(xangle <0){
            xangle = xangle;
        }
        if(xangle >0 ){
            xangle = -xangle;
        }}
    if(lasthit == LAST_HIT_RIGHT){

    if(xangle <0){
            xangle = xangle;
        }
        if(xangle > 0){
            xangle = -xangle;
        }}

    if(lasthit == LAST_HIT_TOP){
        if(yangle < 0){
            yangle = yangle;
        }
        if(yangle > 0){
            yangle = -yangle;
        }}
    if(lasthit == LAST_HIT_BOTTOM){
        if(yangle < 0){
            yangle = yangle;
        }
        if(yangle > 0){
            yangle = -yangle;
        }}
} 

Can you see what I am doing wrong?
The defines is to detect if the ball last hit the left or right side, the top or the paddle

[CyberCarsten]

If it helps, here is the complete source code