Chaning direction

[CyberCarsten]

In my breakout game, I have a slight problem with the direction...
When the ball comes towards the ball, lets say with f(x)=-2x, and the ball hits the paddle on the far most left side, I want the ball to go back in the same direction, but I have found that kinda tricky!
Anyone know how to do this???
I know it has something to do with inverse function....But how to express it, I dont know....

[SLH]

Not sure exactly how you're doing the velocity of the ball, but to get it to bounce like that, just invert the horizontal element (multiply by -1).

[CyberCarsten]

I do it like this:

ball.xv = 2;
ball.yx = -6;
Move_BOB(&ball); 

I tried multiplying ball.xv by -1, but it didn't work....very tricky...

[SLH]

Could you post your move_bob code please?


P.S. I take it ball.xv and ball.yv are the horizontal and vertical speeds of the ball respectivly.

[McCain]

Check this out
http://www.vbforums.com/showthread.p...hreadid=219448

[CyberCarsten]

Function prototype:

int Move_BOB(BOB_PTR bob)
{
// this function moves the bob based on its current velocity
// also, the function test for various motion attributes of the'
// bob and takes the appropriate actions
   

// is this a valid bob
if (!bob)
   return(0);

// translate the bob
bob->x+=bob->xv;
bob->y+=bob->yv;

// test for wrap around
if (bob->attr & BOB_ATTR_WRAPAROUND)
   {
   // test x extents first
   if (bob->x > max_clip_x)
       bob->x = min_clip_x - bob->width;
   else
   if (bob->x < min_clip_x-bob->width)
       bob->x = max_clip_x;
   
   // now y extents
   if (bob->x > max_clip_x)
       bob->x = min_clip_x - bob->width;
   else
   if (bob->x < min_clip_x-bob->width)
       bob->x = max_clip_x;

   } // end if
else
// test for bounce
if (bob->attr & BOB_ATTR_BOUNCE)
   {
   // test x extents first
   if ((bob->x > max_clip_x - bob->width) || (bob->x < min_clip_x) )
       bob->xv = -bob->xv;

   // now y extents 
   if ((bob->y > max_clip_y - bob->height) || (bob->y < min_clip_y) )
       bob->yv = -bob->yv;

   } // end if

// return success
return(1);
} // end Move_BOB 

P.S. I take it ball.xv and ball.yv are the horizontal and vertical speeds of the ball respectivly.

Yes, they are

[SLH]

Is the problem that the ball is wrapping off the screen first? because this will happen if it's moving faster than its width.

The problem may also be that the ball gets 'stuck' constantly changing it's direction, so solve this do seperate checks for the left and right edges using xv = abs(xv) and xv = -abs(xv) respectivly (assuming abs is a valid function that gets the modulus of it's parameter).




Regarding bouncing off the players pad, check the x location of the ball, in relation to the middle of the pad, then if it's far-enough away (yet still hits the pad), then invert the x and y velocities of the ball).

[CyberCarsten]

Thank you for your reply
It only bounces if the BOB (Blitter object) was created with BOB_ATTR_BOUNCE.
&ball is not created with this parameter.....
Where should I use the abs function??

[SLH]

Did you try changing the xv values using the abs function?

What happens at the moment? Does the ball just continue off the edge of the screen?


Assuming you understood what i've ment, i can't see how it wouldn't work unless there's something wrong somewhere else.

[CyberCarsten]

The bounce of the wall worked perfect from the beginning, also bouncing of blocks, its just when the ball hits the paddle on the far left and right side it should bounce back in the same direction that it came in with....
I didn't quite understand where to put the abs function.....

[CyberCarsten]

This is the paddle code:

// the ball has hit the paddle 
if(Collision_BOBS(&ball,&paddle)){ 
    if(ball.x == paddle.x && paddle.x <=19) { // Hits paddle on far left
    xangle = xangle *(-1);
    }
    
    if(ball.x > 59 && paddle.x <=74){ // Hits paddle on far right
    xangle = xangle *(-1);
    }
yangle = -yangle;
} 

Where I have set ball.xv and ball.yx to xangle and yangle respectivily.

[SLH]

Try this:

if(Collision_BOBS(&ball,&paddle)){  
    if(abs(ball.x-(paddle.x+paddle.width/2)) > (paddle.width/4)) { // Hits paddle on far left or the far right
        if(ball.x<(paddle.x+paddle.width/2) { //it hit the left
            xangle = -abs(xangle);
        }
        else { //it hit the right
            xangle = abs(xangle);
        }
    } 
    yangle = -abs(yangle); //assuming -ve velocity is up
} 

P.S. sorry for the late reply.

[CyberCarsten]

No problem
I'll try it now!

[CyberCarsten]

Hi again
It works when the ball hits the left side of the paddle, but when it hits the right side it either goes right trough the paddle or goes in the oppisite direction....

[SLH]

Is the ball very wide (relative to it's velocity/the paddle?) if so then doing the following *may* fix it. If not then i'm not sure of the problem, because i'm pretty sure the code i gave should work.

change ball.x to ball.x+ball.width/2

[CyberCarsten]

The ball is 12 pixels wide....I tried the replacement, but that didn't work either.....

[SLH]

Could you put a breakpoint in here:

if(ball.x<(paddle.x+paddle.width/2) { //it hit the left

and here:

xangle = abs(xangle);

then tell me whether the code gets to them both successfully when the ball should bounce of the right of the pad (the ball has to be in the far right quarter of the pad). I'm really stumpped here though.


EDIT: changed the first breakpoint, i copyed the wrong one by mistake.

[CyberCarsten]

dont know how to do breakpoints......

[SLH]

In MS Visual C++ you move the cursor to the line of code, and press F9. Then run the project (F5 not ctrl-F5).


If you want to upload your project i could have a look at it for you.

[CyberCarsten]

Yes, i will upload it in about an hour...my pc is busy at the moment....

[SLH]

Ok, i'll have a look at it when i have a moment.

[CyberCarsten]

Thanks
My girlfriend will soon be finished with my computer, so I can send it...

[CyberCarsten]

Do you want the entire project with bitmaps, its about 12 mb, or just the source???

[SLH]

I'd need the bitmaps as well.

[CyberCarsten]

Luckilly it wasn't 12 megs, counted the debug info in...
So here it is:
main.cpp -> main source file
GPBUMB1-3.cpp/.h -> Game Engine

Used DirectX SDK 6.1 - can't get it to compile with higher sdk version
Needed to compile:
ddraw.h
dinput.h
dsound.h

ddraw.lib
dinput.lib
dsound.lib
winmm.lib
dxguid.lib

[CyberCarsten]

Altough it can compile with a higher sdk version if direct input support is left out(has to be deleted from gpdum3.h/cpp)

[SLH]

Ok, i've had a look at it but couldn't get it to compile. I've had a look at your code, and the only thing that *may* be the problem is with your Collision_BOBS code. I'm not too sure how it works, so it may be perfectly fine though.

Here's code i'd use though.... (not syntactically tested)

int Collision_BOBS(BOB_PTR bob1, BOB_PTR bob2)
{
// are these a valid bobs
if (!bob1 || !bob2)
   return(0);

// test if rects overlap
if (bob1->x <= (bob2->x+bob2->width))
   if ((bob1->x+bob1->width) >= bob2->x)
      if (bob1->y <= (bob2->y+bob2->height))
         if ((bob1->y+bob1->height) >= bob2->y)
            return(1);
// if we got here then there's no collision
return(0);

} // end Collision_BOBS 

Sorry i can't be of more help. It would be useful if you could work out how to add breakpoints and tell me the results (as i can't because i can't compile the project).

[CyberCarsten]

Thank you for your reply and for looking at the code
I'll try to do breakpoints today, and tell you what the outcome is.

[CyberCarsten]

I tried adding breakpoints to the code, but nothing happend...it just compiles and run....

[SLH]

How did you compile? You need to "Start Debug" (pressing F5 in MS Visual C++).

I don't think a straight compile will stop at breakpoints. To test if the breakpoints are working just put one on a line you *know* will get excecuted.

[CyberCarsten]

yeah, I did that, but it just executed as usual....

[SLH]

Sorry, but i have no idea what could be wrong. If your program doesn't stop at breakpoints then it's very hard to work out what's wrong with your code.

[CyberCarsten]

yeah ....damn it!
But thank you for all of your help!