# How do I make a 2D race car turn smoothly? [duplicate]

I'm making a competitive 2-player 2D racing game for a school project. I'm struggling with the movements of my car: I made it a square for testing purposes and it can move left, right, up or down, but it can't make smooth turns around corners.

How can I make my car (currently a square) make smooth movements? I've heard vectors might help, but I don't know how to use them.

I'm writing this in C# with Visual Studio.

My car control code looks like this right now:

private void Form1_KeyDown(object sender, KeyEventArgs key) {
// player1 controls
if (key.KeyCode == Keys.Up)     { Player1.Top -= 5; }
if (key.KeyCode == Keys.Down)   { Player1.Top += 5; }

if (key.KeyCode == Keys.Left)   { Player1.Left -= 5; }
if (key.KeyCode == Keys.Right)  { Player1.Left += 5; }

// player2 controls
if (key.KeyCode == Keys.W) { Player2.Top -= 5; }
if (key.KeyCode == Keys.S) { Player2.Top += 5; }

if (key.KeyCode == Keys.A) { Player2.Left -= 5; }
if (key.KeyCode == Keys.D) { Player2.Left += 5; }
}

• You need to rotate the car while it's moving and then move it in the direction it facing. The keys should affect velocity and not movements directly in the sense that keys control acceleration. Oct 23, 2014 at 10:41
• We heared that, only the code of that is so hard to figure out :s Oct 23, 2014 at 12:22
• @elipoo X = speed * cos( rotation ), Y = speed * sin( rotation ). It's that easy.
– Ben
Oct 23, 2014 at 14:48
• This question has some good information, specifically in this answer. Oct 23, 2014 at 16:15
• @Ben still figuring out how.. Oct 24, 2014 at 8:00

Start by adding a variable for the angle that the car is moving at.

float angle = Math.Pi / 2;


Then add a variable for the current speed.

float speed = 0.0;


Now create three constants:

public static final float acceleration = 0.1; public static final float maxSpeed = 5.0; public static final float rotationRate = Math.Pi / 50;

For starters, get your controls somewhat right:

Do this every frame:

private void everyTick()
{
player.top -= Math.sin(Player1.angle) * Player1.speed;
player.left += Math.cos(Player1.angle) * Player1.speed;
}


Do this on key press:

private void Form1_KeyDown(object sender, KeyEventArgs key)
{
//player1 controls
if (key.KeyCode == Keys.Up)
{
Player1.speed += accelaration;
Player1.speed = Math.min(Player1.speed,maxSpeed);
}
if (key.KeyCode == Keys.Down)
{
Player1.speed -= accelaration;
Player1.speed = Math.max(Player1.speed, -maxSpeed);
}
if (key.KeyCode == Keys.Left)
{
Player1.angle += rotationRate;
}
if (key.KeyCode == Keys.Right)
{
Player1.angle -= rotationRate;
}

}


This should get you started.

• private void Player(string[] args ) { double angle = Math.Pi / 2; double speed = 0.0; } public void final(float[ ]args) { const double acceleration = 0.1; } public void final(float[ ]args) { const double maxSpeed = 5.0; } public void final(float[ ]args) { double rotationRate = Math.Pi / 50; } Oct 24, 2014 at 10:37
• this is youre 2 first steps, dont know if i'm doing it right but it gives a lot of errors right now. Oct 24, 2014 at 10:40

First use Zehelvion answer to make the car turn correctly, then:

Use the timestamp, you measure how much time it took for your last iteration and use that to modulate the speed at which you are changing things.

void RunGame(float deltatime)
{
if (key.KeyCode == Keys.Up)
{
Player1.speed += accelaration * deltatime
Player1.speed = Math.min(Player1.speed,maxSpeed)
...


This will make it much smoother even if the framerate goes up or down (why accelerate twice as fast if the framerate goes from 30 to 60 in some area?).

• i'm still trying to use the code of Zehelvion only the variable and constant part isnt really working so have to fix that. After that i will try this :). Oct 24, 2014 at 15:22