More begginer stuff : Enemies and rotation -code snippet-

[Cristian]

Hi I'm back!
This time with a pretty requested feature, rotating enemies to face the player (or any other node) and move towards it.
Well let's get started

1) Turning the node(The function is not mine. I found it while searching the forums)

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vector3df getTargetAngle(vector3df v, vector3df r) 
{
   //v -current node position
   //r -target node position

   vector3df angle; 
   float x,y,z; 
   x = r.X - v.X; 
   y = r.Y - v.Y; 
   z = r.Z - v.Z; 
    
   //angle in X-Z plane 
   angle.Y = atan2 (x, z); 
   angle.Y *= (180 / PI); //converting from rad to degrees 
    
   //just making sure angle is somewhere between 0-360 degrees 
   if(angle.Y < 0) angle.Y += 360; 
   if(angle.Y >= 360) angle.Y -= 360; 
    
   //angle in Y-Z plane while Z and X axes are already rotated around Y 
   float z1 = sqrt(x*x + z*z); 
    
   angle.X = atan2 (z1, y); 
   angle.X *= (180 / PI); //converting from rad to degrees 
   angle.X -= 90; 
    
   //just making sure angle is somewhere between 0-360 degrees 
   if(angle.X < 0) angle.X += 360; 
   if(angle.X >= 360) angle.X -= 360; 

   return angle; 
}

2) getting the distance

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f64 getDistance(ISceneNode* sn1 ,ISceneNode* sn2) 
{ 
     vector3df pos = sn1->getPosition(); 
     return  pos.getDistanceFrom(sn2->getPosition());  
}

3) and finally, in your let's say Enemy::Update() function
do something like:

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core::vector3df facing( sin( enemyNode->getRotation().Y * PI/180.0f ), 0, cos( enemyNode->getRotation().Y * PI/180.0f ) ); 
facing.normalize();  
[your enemy node]->setPosition([your enemy node]->getPosition()+(facing*[movement speed]));

Of course you should check if the player is in range of the enemy, for example my ESpider has 3 states:
1) if (getDistance(Spider1 ,Player)<50). In this state the enemy faces the target, showing that it's aware of his presence.
2) if (getDistance(Spider1 ,Player)<30). In this state the enemy advances towards the player, until...
3) if (getDistance(Spider1 ,Player)<15). The enemy attacks the player!
Of course this type of behaviour is good only for animals and crappy monsters.
A human enemy should also try to dodge any ranged weapons.
To dodge or strafe modify the "facing.X" or "facing.Z" values ("facing" is the vector in the code).
Also, keep in mind that Irrlicht does NOT time events, so you must do it manually.
A good & simple example is Emil_halim's CTimer class for BCX.

Here's its adaptation for C++:

CTime.cpp

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#include <irrlicht.h>

using namespace irr;
using namespace core;

static u32 _Basetime;
void TimeInit(IrrlichtDevice* device)
 {
     _Basetime = device->getTimer()->getTime();
 }
class TTime
 {
    
       u32  startTime;
       u32  endTime;
       bool Active;
    public:
       TTime(u32 start,u32 duration)
        {
           startTime  = start + _Basetime ;
           endTime    = startTime + duration;
           Active     = true;
        }
        
       ~TTime () {}
       
       bool CheckTime(IrrlichtDevice* device)
        {
            if (!Active)return false;
            u32 tick  = device->getTimer()->getTime();
            if (tick > startTime && tick < endTime)
               return true;
            else
               return false;
        }
        
       bool CheckStartTime(IrrlichtDevice* device)
        {
            if (!Active)return false;
            u32 tick  = device->getTimer()->getTime();
            if (tick > startTime)
               return true;
            else
               return false;
        } 
         
       bool CheckEndTime(IrrlichtDevice* device)
        {
            if (!Active)return false;
            u32 tick  = device->getTimer()->getTime();
            if (tick > endTime)
               return true;
            else
               return false;
        } 
        
       void UpdateTime(u32 start,u32 duration)
        {
           startTime  = start + _Basetime;
           endTime    = startTime + duration;
        }   
        
       void Enable()
        {
             Active     = true;
        }
        
       void Disable()
        {
             Active     = false; 
        } 
        
       void setAfter(TTime& other ,u32 period)
        {
             startTime  = other.startTime + period;
             endTime    = other.endTime + period;
        }         
        
       void setAS(TTime& other)
        {
             startTime  = other.startTime;
             endTime    = other.endTime;
        }            
};

Bye. See u all later.

[bish]

Thx, there are some realy usefull functions there.

[Xico]

Hi, instead of:

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   if(angle.X < 0) angle.X += 360;
   if(angle.X >= 360) angle.X -= 360; 

you can use modulus to contrain in between 0 and 359:

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angle.X = angle.X % 359; 

or:

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angle.X = (angle.X-90) % 359; 

[hearsedriver]

you can use modulus to contrain in between 0 and 359:

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angle.X = angle.X % 359; 

or:

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angle.X = (angle.X-90) % 359; 

It should read "% 360". Modulo is the rest of the division, hence to get values between 0 and 359 you need the rest of the division by 360. Anyway, we're talking about floats here, so the right method is fmodf.

~hearsedriver();