Hello, I am attempting to make a 3d space game with spaceships and all that. I have it set up to load models but now I am trying to make the space ship have the "space" feel. I want it to when user presses a key, it goes forward pretty fast then slowly slows down like a ship would do. I don't want instant stops This is what I have so far. void Keyboard(unsigned char key, int x, int y) { #pragma unused (x, y) bool flag = false; rads=roty*(PI/180.0f); //convert degrees to radians cosa=cos(rads); sina=sin(rads); switch(key) { case 'w'://Move forward velx += cosa *10; velz += sina*10; } thePlayer.x += velx; thePlayer.z += velz; glutPostRedisplay(); } one of my problems I think is that, this function gets called only when a user presses the key. maybe? velx and vely are the velociy of the player, an thePlayer is the actual player movement. Everytime I press "W" it goes forward but instantly stops. Let me know what I am doing wrong and if you need any more info let me know. Thanks, Nahid569

You should try some simple Euler integration instead, or similar.

Perhaps a bit technical, but: http://en.wikipedia.org/wiki/Euler_integration

The gist of it is this: instead of specifying the acceleration directly, you specify the force of the rockets/thrusters. This is exactly what would happen to a normal spaceship, as the rockets apply a force to the ship. This force "turns" into acceleration, and the acceleration makes the velocity change.

So, as long as the player depresses the "forward" key, have FengineX set to cos(rads)*EnginePower, similar for FengineY. If the key is not pressed, set them to zero.

Then, when updating the physics, first accumulate all forces. Since you want it to slowly halt, you'll want to introduce drag (albeit a bit unrealistic in outer space). A simple way to approximate this is to introduce a force which is proportional to the velocity, but "works" in the opposite direction. So

void AccumulateForces() {
ForceX = ForceY = 0;

ForceX += FengineX;
// compute drag
float dragX = -velX * dragCoefficient;
ForceX += dragX;

.. similar for Y

}

dragCoefficient specifies how "aerodynamical" the ship is. Try with zero first to see that it moves correctly, then try low values (ie 0.01) and adjust.

Next you want to perform the integration. For this you need to select a suitable "timestep" which is basically how large steps you take, and is typically around 30-60fps. Setting this as constant will make it depend on framerate, you can learn about how to fix that later.

float dt = 1.f / 30.f;

The physics. You can read more about the details here: http://www.gaffer.org/game-physics/integration-basics/

void TimeStep(float dt) {

AccumulateForces();

float aX = ForceX * inv_mass;
float aY = ForceY * inv_mass;

velX += dt * aX;
velY += dt * aY;

posX += dt * velX;
posY += dt * velY;
}

where inv_mass = 1 / mass of the ship.

Now, simply call TimeStep(dt) inside your game loop, and use posX and posY for the space ship position.

Think that should be it, though I haven't tested it :)

The property you're describing is related to inertia and the conservation of momentum. Newton's first law sums all of this up well.

Viscosity is the property of a material to disperse the momentum of objects in contact with it. The higher the viscosity, the higher the rate of slow down. The ship should not slow down at all in space, since the vacuum of space is (practically) non-viscous. Since the momentum is not transferred from the ship to the vacuum, the ship must maintain the same velocity in order to ensure the conservation of momentum.

Hey guys THANKS alot!

Those are gread ideas lord and I will use that but first I need to get a way to make a function that runs always. I do not have an idea how to do that. I was thinking of putting the entire movement thing in MAIN function because that is always running but I do not know how to do the keyboard thing outside of Keyboard function.

Is there a better way? Let me know

The heart and soul of any 3D game is a Message loop. This is just an infinite loop that breaks only if the WM_QUIT message is posted to the window. You should handle your main logic updates in that loop and then your rendering functions.

Quote:Original post by nahid569
I want it to when user presses a key, it goes forward pretty fast then slowly slows down like a ship would do

Er, a space ship wouldn't do that. What would make it slow down?
(That is assuming you meant spaceship in the above. If 'ship' refers to an actual sailing ship, it would slow down, yes)

Quote:Original post by Spoonbender

Quote:Original post by nahid569
I want it to when user presses a key, it goes forward pretty fast then slowly slows down like a ship would do

Er, a space ship wouldn't do that. What would make it slow down?
(That is assuming you meant spaceship in the above. If 'ship' refers to an actual sailing ship, it would slow down, yes)

Was about to post the same. On earth what makes things slow down is various forms of friction: air resistance, ground friction, friction of moving parts.

In space there is a pretty good vacuum meaning there are none of these frictional forces. In space, a ship that's moving will effectively keep moving forever until it slows itself down with it's engines by producing a trust in the opposite direction. (I say "effectively" because space is not a perfect vacuum so over galactic distances there would perhaps be enough 'air resistance' to eventually slow you down)

-me