Tank rotation

[Angeljruiz]

Hey everybody

I was wondering how i could simulate tank like movement.
What i was planing on doing is changing the rotation using left and right keys (Already using a library for input) then moving the tank with both the up and down keys. Usually movements pretty easy as in if the right button is pressed then increase the x coord but i wouldnt know how to do that with rotation. Sorry, its kind of hard for me to explain.

[Stewbond]

Tank heading += TurningRate * LeftKeyPressed
Tank heading -= TurningRate * RightKeyPressed

Tank X Position += cos(Tank heading) + MovementRate * FwdKeyPressed
Tank X Position -= cos(Tank heading) + MovementRate * AftKeyPressed

Tank Y Position += sin(Tank heading) + MovementRate * FwdKeyPressed
Tank Y Position -= sin(Tank heading) + MovementRate  * AftKeyPressed

[Angeljruiz]

Why multiply the turning rate by LeftKeyPressed?

[jgeorge]

The exact implementation will differ depending on what libraries you're using to handle keyboard input; however, the rough logic is as follows.

if (W == Pressed) {
    location.x += (cos(0.017453277777 * heading)) * speed;
    location.y += (sin(0.017453277777 * heading)) * speed;
}

else if (S == Pressed) {
    location.x += (cos(0.017453277777 * heading)) * (speed * -1);
    location.y += (sin(0.017453277777 * heading)) * (speed * -1);
}

else if (A == Pressed) {
    heading -= 1;
    if (heading < 0) heading = 360;
}

else if(D == Pressed) {
    heading += 1;
    if (heading > 360) heading = 0;
}

Hopes this helps. If you happen to be using SFML I can help you with implementation

[Angeljruiz]

Its not really working as expected. It only moves if the angle is just right and even then it just moves up.
Heres my code

void CheckKeys()
{
    
    if (!kLeft && !kRight && !kUp && !kDown)
    {
        KeyDown = false;
        return;
    }
    
    KeyDown = true;
    
    if (kLeft)
    {
        if (KeyCounter >= KeyTick)
        {
            TankRotation -= 1;
            Redraw = true;
            KeyCounter = 0;
        }
    }
    
    if (kRight)
    {
        if (KeyCounter >= KeyTick)
        {
            TankRotation += 1;
            Redraw = true;
            KeyCounter = 0;
        }
    }
    
    if (kUp)
    {
        if (KeyCounter >= KeyTick)
        {
            TankX += (cos(0.017453277777 * TankRotation)) * Speed;
            TankY += (sin(0.017453277777 * TankRotation)) * Speed;
            Redraw = true;
            KeyCounter = 0;
        }
    }
        
}

and im drawing it using this

            al_draw_rotated_bitmap(Tank, 32, 32, TankX, TankY, TankRotation*0.017453277777, NULL);

Tank is the bitmap im drawing, both 32s are the x and y values of the middle of the bitmap, the next to arguments are the screen coords im drawing to, and the next is the angle to rotate by

[o1vk4iN6]

Well for converting from deg to rad I would use a name instead of the actual number or an inlined function might be even better. It also seems everything is a global variable, why not make a class call it, vec2 use that for position instead, then make a class for tank or entity to hold the position etc...

[Angeljruiz]

Well how would you convert it exactly?
And i know everythings a global right now, im just going to leave it as is right now.

[o1vk4iN6]

It's a simple mathematical equation you learn in highschool. 0.017blahblah is just PI / 180. It really is simple when you think about it. 2PI is a complete circle in degrees it is 360, so 2PI/360 is rad per degree (can be simplified to PI/180) that multiplied by any degree will get you the radians, which is what all the mathematical functions use.

Why start a bad habit ? Save it now by removing all the globals before it's too late.

[Angeljruiz]

Oh thats why i dont know that, im still in highschool - My teacher only briefly mentioned sin cos and tang so i dont really know what its used for.
So what i have is

if (kLeft)
    {
        if (KeyCounter >= KeyTick)
        {
            TankRotation -= 1;
            Redraw = true;
            KeyCounter = 0;
        }
    }
    
    if (kRight)
    {
        if (KeyCounter >= KeyTick)
        {
            TankRotation += 1;
            Redraw = true;
            KeyCounter = 0;
        }
    }
    
    if (kUp)
    {
        if (KeyCounter >= KeyTick)
        {
            TankX += (cos(ALLEGRO_PI/180 * TankRotation) * Speed);
            TankY += (sin(ALLEGRO_PI/180 * TankRotation) * Speed);
            Redraw = true;
            KeyCounter = 0;
        }
    }
    
    if (kDown)
    {
        if (KeyCounter >= KeyTick)
        {
            TankX += (cos(ALLEGRO_PI/180 * TankRotation)) * (Speed * -1);
            TankY += (sin(ALLEGRO_PI/180 * TankRotation)) * (Speed * -1);
            Redraw = true;
            KeyCounter = 0;
        }
    }

    al_draw_rotated_bitmap(Tank, 32, 32, TankX, TankY, TankRotation*(ALLEGRO_PI/180), NULL);

But its still not working as expected, it rotates fine and smooth but it doesnt move as it should. Thanks for your help so far though.
And ehh i know globals are bad. Ill fix it right now