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collision detection

Started by phil67rpg Dec 2, 2012 at 11:08 PM 14 replies 2.4k views

Original Post

Dec 2, 2012 at 11:08 PM

I am using the following code to implement collision detection between a ball and bricks in a breakout game. My problem is that when I run the program the ball instantly vanishes from the screen. I have been working on this problem for quite some time. I have also been doing a lot of studying on c++ and collision detection.
[code}
void brick_collision()
{
if(x>3.0f && x<5.0f)
{
brick=3.0f;
bricks[3][5]=false;
}

else if(x>1.0f && x<3.0f)
{
brick=1.0f;
bricks[3][4]=false;
}

else if(x>-1.0f && x<1.0f)
{
brick=-1.0f;
bricks[3][3]=false;
}

else if(x>-3.0f && x<-1.0f)
{
brick=-3.0f;
bricks[3][2]=false;
}

else if(x>-5.0f && x<-3.0f)
{
brick=-5.0f;
bricks[3][1]=false;
}

SPRITE object3;
SPRITE object4;

object3.x=x;
object3.y=y;
object3.width=0.1f;
object3.height=0.1f;

object4.x=brick;
object4.y=3.5f;
object4.width=2.0f;
object4.height=1.0f;

if(Sprite_Collide(&object3,&object4)==1)
{
xstep=-xstep;
ystep=-ystep;
}
}

BaneTrapper

Dec 3, 2012 at 8:55 AM

Am gonna provide rectangle on rectangle collision


 //X = starting position X
 //Y = starting position Y
 //W = Width of the rectangle
 //H = Height of the rectangle
 rec1;//x y w h
 rec2;//x y w h
 //The way we gonna check collision is
 //From left
 //From right
 //From top
 //From bottom
 if(rec1.x + rec1.w > rec2.x &&
 rec1.x < rec2.x + rec2.w &&
 rec1.y + rec1.h > rec2.y &&
 rec1.y < rec2.y + rec2.w )

EDIT::
I have noticed there is a tag for OpenGL? your checking collision in 3D?

phil67rpg

Dec 3, 2012 at 10:06 PM

actually I am working in 2d for now

Khatharr

Dec 4, 2012 at 1:20 AM

Hi, Phil.

Edit: Okay, I can see you tried, so I'll help you out some.

Hit edit on your first post there.
Delete all the code.
Copy the code (with formatting) from the original file.
In the edit window, place the keyboard cursor where the code you deleted used to be.
At the top of the edit window there are two rows of buttons. Press the red button at the end of the second row:
Select your language from the drop-down list.
Past your code into the open space.
Click 'OK'.
Click 'Save Changes'.

Typically I use something like the following for rect vs rect:
[source lang="cpp"]//using Microsoft RECT (left, top, right, bottom)

bool rectCollideTest(RECT& thisRect, RECT& thatRect) {
if(thisRect.left > thatRect.right) {return false;}
if(thisRect.right < thatRect.left) {return false;}
if(thisRect.top > thatRect.bottom) {return false;}
if(thisRect.bottom < thatRect.top) {return false;}
return true;
}[/source]

This can also be accelerated slightly if you know which exclusion is most likely and move it to the top. That's not something to worry about unless you're doing more collisions than you should though.

phil67rpg

Dec 4, 2012 at 1:42 AM

sorry about code posting I will be more careful in the future.

Khatharr

Dec 4, 2012 at 1:49 AM

The [ code ] tags aren't working correctly anyway, so make sure to use the button.

phil67rpg

Dec 4, 2012 at 2:23 AM

I have one more question, how would one turn off a brick after hitting it with a ball?

Khatharr

Dec 4, 2012 at 2:32 AM

That would probably have something to do with whatever it means for a brick to be 'on' or 'off' in your code.

phil67rpg

Dec 4, 2012 at 2:36 AM

[source lang="cpp"]void check_collision()
{
if(x>=3.0f && x<=5.0f && y>=3.5f && y<=4.0f)
{
bricks[3][5]=false;
glRectf(3.0f,4.0f,5.0f,3.5f);
ystep=-ystep;
}
well here is the code I am using so far.

if(x>=1.0f && x<=3.0f && y>=3.5f && y<=4.0f)
{
bricks[3][4]=false;
glRectf(1.0f,4.0f,3.0f,3.5f);
ystep=-ystep;
}

if(x>=-1.0f && x<=1.0f && y>=3.5f && y<=4.0f)
{
bricks[3][3]=false;
glRectf(-1.0f,4.0f,1.0f,3.5f);
ystep=-ystep;
}

if(x>=-3.0f && x<=-1.0f && y>=3.5f && y<=4.0f)
{
bricks[3][2]=false;
glRectf(-3.0f,4.0f,-1.0f,3.5f);
ystep=-ystep;
}

if(x>=-5.0f && x<=-3.0f && y>=3.5f && y<=4.0f)
{
bricks[3][1]=false;
glRectf(-5.0f,4.0f,-3.0f,3.5f);
ystep=-ystep;
}
}
[/source]

phil67rpg

Dec 4, 2012 at 2:37 AM

well I tried using the code button, sorry maybe the code html works.

Khatharr

Dec 4, 2012 at 3:02 AM

The 'code' button actually uses 'source' tags to wrap your code.

Looking over what you posted, I still don't know what's representing a brick in your code.

Looking at your first post it seems like you're just using sprites and treating them like objects. If you want bricks that do things then you should make a class for bricks that encapsulates their behavior.

Separate your drawing from your logic: Do the logic for the frame and then draw the result.