Chapter 5 - How to Detect the Collisions - cocos2d-x

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Chapter 5 - How to Detect the Collisions

Our hero could fire bullets now, but the bullets are only adornments, how could they kill the monsters?

In this chapter, we will introduce Collision Detection to realize the effect.

Firstly, it’s necessary to trace the monsters and the bullets.

In the game, we add a tag for this two kinds of sprites to discriminate them. When tag = 1, it signs a monster, and tag = 2 means a bullet. Because there is already a member named m_nTag of CCNode, and the methods setTag() and getTag() also exist, CCSprite has inherit them, and we could utilize them.

Add the two member variabls below to HelloWorld in HelloWorldScene.h, this two member variables are used to cache the existing monsters and bullets.

1//c p p w i t h c o c o s2d-x

2p r o t e c t e d:

3c o c o s2d::C C M u t a b l e A r r a y*_t a r g e t s;

4c o c o s2d::C C M u t a b l e A r r a y*_p r o j e c t i l e s;1//o b j c w i t h c o c o s2d-i p h o n e

2N S M u t a b l e A r r a y*_t a r g e t s;

3N S M u t a b l e A r r a y*_p r o j e c t i l e s;

In cocos2d-x, CCMutableArray is realized as iOS SDK’s NSMutableArray, its members are NSObjects and their subclasses. Something different is that you should specify the concrete category of its members.

Then initialize the two variables in the construct function, new them in init(), and release them in the destruct function.

1//c p p w i t h c o c o s2d-x

2

3//i n i n i t()

4//I n i t i a l i z e a r r a y s

5_t a r g e t s=n e w C C M u t a b l e A r r a y;

6_p r o j e c t i l e s=n e w C C M u t a b l e A r r a y;

7

8H e l l o W o r l d::~H e l l o W o r l d()

9{

10i f(_t a r g e t s)

11{

12_t a r g e t s->r e l e a s e();

13_t a r g e t s=N U L L;

14}

15

16i f(_p r o j e c t i l e s)

17{

18_p r o j e c t i l e s->r e l e a s e();

19_p r o j e c t i l e s=N U L L;

20}

21

22//c p p d o n't n e e d t o c a l l s u p e r d e a l l o c 23//v i r t u a l d e s t r u c t o r w i l l d o t h i s

24}

25

26H e l l o W o r l d::H e l l o W o r l d()

27:_t a r g e t s(N U L L)

28,_p r o j e c t i l e s(N U L L)

29{

30}

1//o b j c w i t h c o c o s2d-i p h o n e

2//i n i n i t()

3//I n i t i a l i z e a r r a y s

4_t a r g e t s=[[N S M u t a b l e A r r a y a l l o c]i n i t];

5_p r o j e c t i l e s=[[N S M u t a b l e A r r a y a l l o c]i n i t]; 6

7-(v o i d)d e a l l o c

8{

9[_t a r g e t s r e l e a s e];

10_t a r g e t s=n i l;

11

12[_p r o j e c t i l e s r e l e a s e];

13_p r o j e c t i l e s=n i l;

14

15//d o n't f o r g e t t o c a l l"s u p e r d e a l l o c"

16[s u p e r d e a l l o c];

17}

Now modify addTarget() to add a new target to targets array, and set its tag to be 1.

1//c p p w i t h c o c o s2d-x

2//A d d t o t a r g e t s a r r a y

3t a r g e t->s e t T a g(1);

4_t a r g e t s->a d d O b j e c t(t a r g e t);1//o b j c w i t h c o c o s2d-i p h o n e 2//A d d t o t a r g e t s a r r a y

3t a r g e t.t a g=1;

4[_t a r g e t s a d d O b j e c t:t a r g e t];

Modify ccTouchesEnded() to add a new bullet to bullets array, and set its tag to be 2.

1//c p p w i t h c o c o s2d-x

2//A d d t o p r o j e c t i l e s a r r a y

3p r o j e c t i l e->s e t T a g(2);

4_p r o j e c t i l e s->a d d O b j e c t(p r o j e c t i l e);1//o b j c w i t h c o c o s2d-i p h o n e

2//A d d t o p r o j e c t i l e s a r r a y

3p r o j e c t i l e.t a g=2;

4[_p r o j e c t i l e s a d d O b j e c t:p r o j e c t i l e];

Then, modify spriteMoveFinished() as follows. Here we remove the sprites from their corresponding arrays.

1//c p p w i t h c o c o s2d-x

2v o i d H e l l o W o r l d::s p r i t e M o v e F i n i s h e d(C C N o d e*s e n d e r) 3{

4C C S p r i t e*s p r i t e=(C C S p r i t e*)s e n d e r;

5t h i s->r e m o v e C h i l d(s p r i t e,t r u e);

6

7i f(s p r i t e->g e t T a g()==1)//t a r g e t

8{

9_t a r g e t s->r e m o v e O b j e c t(s p r i t e);

10}

11e l s e i f(s p r i t e->g e t T a g()==2)//p r o j e c t i l e

12{

13_p r o j e c t i l e s->r e m o v e O b j e c t(s p r i t e);

14}

15}

1//o b j c w i t h c o c o s2d-i p h o n e

2-(v o i d)s p r i t e M o v e F i n i s h e d:(i d)s e n d e r

3{

4C C S p r i t e*s p r i t e=(C C S p r i t e*)s e n d e r; 5[s e l f r e m o v e C h i l d:s p r i t e c l e a n u p:Y E S]; 6

7i f(s p r i t e.t a g==1)//t a r g e t

8{

9[_t a r g e t s r e m o v e O b j e c t:s p r i t e];

10}

11e l s e i f(s p r i t e.t a g==2)//p r o j e c t i l e 12{

13[_p r o j e c t i l e s r e m o v e O b j e c t:s p r i t e]; 14}

15}

The function update() below is used to detect collisions every frame, remove the collided bullet and monster from the scene. Declare it in HelloWorldScene.h and Define it in HelloWorldScene.cpp.

1//c p p w i t h c o c o s2d-x

2v o i d H e l l o W o r l d::u p d a t e(c c T i m e d t)