Asteroids

Overheal

I have the ship rotating ok and it moves...but the direction it moves in is never predictable: just anytime you rotate the ship it seems to pick a new random vector to accelerate on. :mad:

struct vector{
        float x;
        float y;
};

//return the vector v about an angle,
vector Rotate(vector v, float angle){
        vector temp;

        temp.x=v.x*cos(angle) - v.y*sin(angle);
        temp.y=v.x*sin(angle) + v.y*cos(angle);


        return temp ;
}

// return a vector multiplied by a scalar
vector Mult(vector v, float s){
        vector temp;

        temp.x=v.x*s;
        temp.y=v.y*s;

        //do math
        return temp;
}
//return the addition of two vectors
vector Add(vector a, vector b){
        vector c;
        c.x=a.x+b.x;
        c.y=a.y+b.y;

        //do math
        return c;
}


//////////////////////////////////////////////////////////////////////////////////////
//Ship
//////////////////////////////////////////////////////////////////////////////////////
// the ship struct will store info about our space ship
const int SHIP_NUM_POINTS=4; //number of points in ship's polygon
struct Ship{
        vector points[SHIP_NUM_POINTS]; //points of ship's polygon
        vector position;        // ships location
        vector velocity;        // direction the ship is currently moving
        vector direction;       // direction ship is currently pointing
        float rateOfAccel;      // how fast can we accelerate
        float friction;         // how fast do we slow down
        float rotation;         // how fast do we spin
        int radius;             // the size of the circle which contains the ship
        bool alive;             // whether the ship is alive or dead
}theShip;                       // our global ship structure

void InitShip(Ship* ship){
        //initialise the ships position, velocity and polygon points
        ship->points[0].x=0; //points of ship's polygon (Rotational Origin)
        ship->points[0].y=0; //
        ship->points[1].x=15; //points of ship's polygon (Port Fin)
        ship->points[1].y=10; //
        ship->points[2].x=0; //points of ship's polygon (Prow/Gunmount)
        ship->points[2].y=-30; //
        ship->points[3].x=-15; //points of ship's polygon (starboard Fin)
        ship->points[3].y=10; //

        ship->direction.x= 1;
        ship->direction.y= 0;

        ship->velocity.x =0;
        ship->velocity.y =0;

        ship->rateOfAccel = 0.1;

        ship->position.x=100;
        ship->position.y=100;
        ship->rotation = 0.0; //in float Radians
}

void UpdateShip(Ship* ship){
        // update the ship for the next frame
        /* things to do
        1. check left/right keys and turn(rotate) ship
        2. check up key and accelarate ship
        3. set new position based on current velocity
        4. wrap around edges
        */


        if(theKeys.up==true)
        {
                //ship->position.x++;
                //ship->position.y++; //**MODIFY: SET ACCELERATION VECTOR
                ship->rateOfAccel += 0.001;
                ship->velocity = Add(ship->velocity, ship->direction); //change direction of movement
        }
        else
        {
                //ship->rateOfAccel -= 0.001;
        }

        if(theKeys.left==true)
        {
                ship->rotation -= 0.15;
                ship->direction = Rotate(ship->direction, ship->rotation);

        }
        if(theKeys.right==true)
        {
                ship->rotation += 0.15;
                ship->direction= Rotate(ship->direction, -ship->rotation);

        }



}

void DrawShip(Ship* ship){

        // draw the ships polygon at current position
        vector pos;



    //    pos=Rotate(ship->direction,ship->rotation);
    //    pos=Mult(pos,ship->rateOfAccel);
     //   pos=Add(pos,ship->position);
        ship->velocity = Mult(ship->velocity,ship->rateOfAccel);//Magnitude calculation
        ship->position = Add(ship->position,ship->velocity);//position change




        pos=Rotate(ship->points[0],ship->rotation);
        pos=Add(pos,ship->position);
        Form1->Canvas->MoveTo(pos.x, pos.y);

        //pos=Rotate(ship->points[1],ship->rotation);
        //pos=Add(pos,ship->position);
        //Form1->Canvas->LineTo(pos.x, pos.y);
        
        pos=Rotate(ship->points[2],ship->rotation);
        pos=Add(pos,ship->position);
        Form1->Canvas->LineTo(pos.x, pos.y);

        //pos=Rotate(ship->points[3],ship->rotation);
        //pos=Add(pos,ship->position);
        //Form1->Canvas->LineTo(pos.x, pos.y);

        //pos=Rotate(ship->points[0],ship->rotation);
        //pos=Add(pos,ship->position);
        //Form1->Canvas->LineTo(pos.x, pos.y);



       // pos=Rotate(ship->direction,ship->rotation);
       // pos=Add(




}

any tips would be great, thanks.

satchmo

I've only had a quick look so I could be wrong, but I don't think you should be accumulating both the rotation and the direction when you press left or right; either reset the direction each time you press the key and work out the full rotation, or think of rotation as just being a per-frame value, which is 0 unless you press a key. I'd recommend the former so you don't lose precision after a whole load of rotations.