I want to move a 2d circle in opengl automatically with constant speed on load and then control it with keyboard to move smoothly.
Right now i have the code to move the circle with keyboard, but it is moving only one unit for every keypress.
I want a smooth movement when keypress and automatic movement when on load.
Use glTranslatef to move your object, or alternatively you can just adjust its position x,y,z by a set amount in each update cycle when the keyboard keys are pressed.
E.g
const float MOVE_AMOUNT = 5.0;
public void Update()
{
if (Keyboard.IsKeyDown("a"))
circle.position.x -= MOVE_AMOUNT;
else if (Keyboard.IsKeyDown("d"))
circle.position.y += MOVE_AMOUNT;
}
NOTE: this is not valid C++ syntax, but it gives the overall logic of what you need to be doing, you should be able to figure it out from this. If you want a glTranslate example please let me know.
Related
I have two rectangles, one of them stationary. Whenever I try to move one towards another I want it to 'slide' rather than getting stuck without being able to move. I use oriented bounding boxes and the code is fairly tested, but I don't know how to avoid them getting stuck.
Currently what I do is this:
o1 = o;
vector2df vxy = o.V;
o1.Pos += vxy;
if(o1.overlaps(o2)){
o1 = o;
o1 += vector2df(0.f, vxy.y);
if(o1.overlaps(o2)){
vxy.y = 0;
}
o1 = o;
o1 += vector2df(vxy.x, 0.f);
if(o1.overlaps(o2)){
vxy.x = 0;
}
}
o1.V = vxy
Which is quite 'dirty' as it just checks if the movement can be done in either X and Y, disabling it if it collides individually.
The velocity is a float, so later it will just add it.
I had thought doing a while loop until it doesn't collide, leaving the smaller value in which it won't collide, but it either doesn't work or is stuck in an infinite loop...
I'm guessing the first thing to do would be to rewind your moving box's movement so that it doesn't collide anymore with your fixed box. Right now your boxes are probably staying in a colliding state, hence the infinite loop.
Then as for determining the new velocity of your moving box, you probably want to get the direction of the edge from your fixed box your moving box is colliding with and set that as your new velocity.
You also might want at some point to multiply this new velocity by the dot product of your initial velocity and your new direction, so that when the moving box goes perpendicular to the fixed box's edge, it basically stops, but if it's going at a sharp angle it doesn't loose much speed.
All of this describes a vastly oversimplified approach, you might want to read more about basic game engines/physics/collision detection if you want a cleaner result.
Hope this helps.
I am editing the rollingball example map from Unreal (in Unreal Engine). I changed it so my ball you grow and melt (it's a snowball), gaining and losing size and mass.
My problem is the control of it. The example map moves the ball by adding torque. My problem is that my mass changes a lot, so I need a torque the changes depending on the size of my ball (not 1:1 as a bigger snowball should still moves slower).
My problem is that my ball seems to accumulate torque and spins a lot (I added a lot of friction to the ball, it did not helped, it just moved the problem a bit). As an example, if I press left for a while, it's gonna go left. Then if I press right, it goes right. But when I stop pressing right, it spins and goes left again.
This is my current code:
void ASnowballBall::MoveRight(float Val)
{
const FVector Torque = FVector(-1.f * getNewTorque(Val), 0.f, 0.f);
Ball->AddTorque(SpringArm->GetComponentRotation().RotateVector(Torque));
}
void ASnowballBall::MoveForward(float Val)
{
const FVector Torque = FVector(0.f, getNewTorque(Val), 0.f);
Ball->AddTorque(SpringArm->GetComponentRotation().RotateVector(Torque));
}
float ASnowballBall::getNewTorque(float Val)
{
return (Val * RollTorque * (log2(Ball->GetMass()))) / 10000;
}
Note: The log was a test to increase the torque slowly with the mass. It's not working well at all. Right now I am using return Val * RollTorque instead, but it's almost as bad.
The control is horrible and I would like to get an idea on how to fix it. If removing the torque would be better, I will change it. I simply want a responsive control that is fun, and where the player still have a sense of the size of the ball (slower when big compared to small).
PS: My original mass is about 500 kg and can go up to 20 000 kg (it's a puzzle game). I did not set the original mass, it's set by Unreal relative to it's size. I could change the mass scale though.
You could try using AddForce instead of AddTorque.
So the speed of the ball is modified every tick like this:
void APlayerBallBearing::Tick(float deltaSeconds)
{
Super::Tick(deltaSeconds);
BallMesh->AddForce(FVector(InputLongitude, InputLatitude, 0.0f) * ControllerForce * BallMesh->GetMass());
}
InputLongitude and InputLatitude are the values that are put in by the user in the current frame for movement in cardinal directions, they correspond to your MoveForward and MoveRight values I reckon.
The controller force is something you need to tweak in order to find the right value for your ball movement. With a value of at least 600.0f I started getting "decent" behaviour.
I cannot help you with the mass though you would need to try that out yourself, the default mass of the ball mesh I used was ~110.
I looked at a bunch of similar questions, and I cannot seem to find one that particularly answers my question. I am coding a simple 3d game, and I am trying to allow the player to pick up and move entities around my map. I essentially want to get a velocity vector that will "push" the physics object a distance from the player's eyes, wherever they are looking. Here's an example of this being done in another game (the player is holding a chair entity in front of his eyes).
To do this, I find out the player's eye angles, then get the forward vector from the angles, then calculate the velocity of the object. Here is my working code:
void Player::PickupOtherEntity( Entity& HoldingEntity )
{
QAngle eyeAngles = this->GetPlayerEyeAngles();
Vector3 vecPos = this->GetEyePosition();
Vector3 vecDir = eyeAngles.Forward();
Vector3 holdingEntPos = HoldingEntity.GetLocation();
// update object by holding it a distance away
vecPos.x += vecDir.x * DISTANCE_TO_HOLD;
vecPos.y += vecDir.y * DISTANCE_TO_HOLD;
vecPos.z += vecDir.z * DISTANCE_TO_HOLD;
Vector3 vecVel = vecPos - holdingEntPos;
vecVel = vecVel.Scale(OBJECT_SPEED_TO_MOVE);
// set the entity's velocity as to "push" it to be in front of the player's eyes
// at a distance of DISTANCE_TO_HOLD away
HoldingEntity.SetVelocity(vecVel);
}
All that is great, but I want to convert my math so that I can apply an impulse. Instead of setting a completely new velocity to the object, I want to "add" some velocity to its existing velocity. So supposing I have its current velocity, what kind of math do I need to "add" velocity? This is essentially a game physics question. Thank you!
A very simple implementation could be like this:
velocity(t+delta) = velocity(t) + delta * acceleration(t)
acceleration(t) = force(t) / mass of the object
velocity, acceleration and force are vectors. t, delta and mass scalars.
This only works reasonably well for small and equally spaced deltas. What you are essentially trying to achieve with this is a simulation of bodies using classical mechanics.
An Impulse is technically F∆t for a constant F. Here we might want to assume a∆t instead because mass is irrelevant. If you want to animate an impulse you have to decide what the change in velocity should be and how long it needs to take. It gets complicated real fast.
To be honest an impulse isn't the correct thing to do. Instead it would be preferable to set a constant pick_up_velocity (people don't tend to pick things up using an impulse), and refresh the position each time the object rises up velocity.y, until it reaches the correct level:
while(entPos.y < holdingEntPos.y)
{
entPos.y += pickupVel.y;
//some sort of short delay
}
And as for floating in front of the player's eyes, set an EyeMovementEvent of some sort that also sends the correct change in position to any entity the player is holding.
And if I missed something and that's what you are already doing, remember that when humans apply an impulse, it is generally really high acceleration for a really short time, much less than a frame. You wouldn't see it in-game anyways.
basic Newtonian/D'Alembert physics dictate:
derivate(position)=velocity
derivate(velocity)=acceleration
and also backwards:
integrate(acceleration)=velocity
integrate(velocity)=position
so for your engine you can use:
rectangle summation instead of integration (numerical solution of integral). Define time constant dt [seconds] which is the interval between updates (timer or 1/fps). So the update code (must be periodically called every dt:
vx+=ax*dt;
vy+=ay*dt;
vz+=az*dt;
x+=vx*dt;
y+=vy*dt;
z+=vz*dt;
where:
a{x,y,z} [m/s^2] is actual acceleration (in your case direction vector scaled to a=Force/mass)
v{x,y,z} [m/s] is actual velocity
x,y,z [m] is actual position
These values have to be initialized a,v to zero and x,y,z to init position
all objects/players... have their own variables
full stop is done by v=0; a=0;
driving of objects is done only by change of a
in case of collision mirror v vector by collision normal
and maybe multiply by some k<1.0 (0.95 for example) to account energy loss on impact
You can add gravity or any other force field by adding g vector:
vx+=ax*dt+gx*dt;
vy+=ay*dt+gy*dt;
vz+=az*dt+gz*dt;
also You can add friction and anything else you need
PS. the same goes for angles just use angle/omega/epsilon/I instead of x/a/v/m
to be clear by angles I mean rotation (pitch,yaw,roll) around mass center
I am using OpenGL to create the 3D space.
I have a spaceship which can fire lasers.
Up until now I have had it so that the lasers will simply to deeper into the Z-axis once fired.
But I am attempting to make a proper aiming system with crosshairs so that you can aim and shoot in any direction, but I have not been successfull in trying to update the laser's path.
I have a directional vector based off the lasers end tip and start tip, which is gotten from the aiming.
How should I update the laser's X,Y,Z values (or vectors) properly so that it looks natural?
I think I see.
Let's say you start with the aiming direction as a 3D vector, call it "aimDir". Then in your update loop add all 3 (x, y and z) to the projectile "position". (OK, at the speed of light you wouldn't actually see any movement, but I think I see what you're going for here).
void OnUpdate( float deltaT )
{
// "move" the laser in the aiming direction, scaled by the amount of time elapsed
// since our last update (you probably want another scale factor here to control
// how "fast" the laser appears to move)
Vector3 deltaLaser = deltaT * aimDir; // calc 3d offset for this frame
laserEndpoint += deltaLaser; // add it to the end of the laser
}
then in the render routine draw the laser from the firing point to the new endpoint:
void OnRender()
{
glBegin(GL_LINES);
glVertex3f( gunPos.x, gunPos.Y, gunPos.z );
glVertex3f( laserEndPoint.x, laserEndPoint.y, laserEndPoint.z );
glEnd();
}
I'm taking some liberties because I don't know if you're using glut, sdl or what. But I'm sure you have at least an update function and a render function.
Warning, just drawing a line from the gun to the end of the laser might be disappointing visually, but it will be a critical reference for adding better effects (particle systems, bloom filter, etc.). A quick improvement might be to make the front of the laser (line) a bright color and the back black. And/or make multiple lines like a machine gun. Feel free to experiment ;-)
Also, if the source of the laser is directly in front of the viewer you will just see a dot! So you may want to cheat a bit and fire from just below or to the right of the viewer and then have in fire slightly up or in. Especially if you have one one each side (wing?) that appear to converge as in conventional machine guns.
Hope that's helpful.
I have recently been getting into OpenGL/SDL and playing around with objects in 2D/3D Space and as i'm sure most newbies to this area do, have a few queries, about the 'best' way to do something. I quote best, because i'm assuming there isn't a best way, it's personal preference.
So, I have an entity, a simple GL_QUAD, which I want to move around. I have keyboard events setup, i can get the keypress/release events, not a problem.
I have an entity class, which is my GL_QUAD, pseudo implementation....
class Entity
{
void SetVelocity(float x, float y);
}
I then have this event handler code...
if theEvent.Key = UPARROW AND theEvent.State = PRESSED
Entity.SetVelocity(0.0f, -1.0f);
else if theEvent.Key = UPARROW AND theEvent.State = RELEASED
Entity.SetVelocity(0.0f, 0.0f);
My question is, is this the best way to move my entity? This has led me to thinking that we could make it a little more complex, by having a method for adjusting the X/Y Velocity, seperately. As SetVelocity would forget me X velocity if i started moving left? So i could never travel diagonally.
For Example...
class Entity
{
void SetXVelocity(float x);
void SetYVelocity(float y);
}
if theEvent.Key = UPARROW AND theEvent.State = PRESSED
Entity.SetYVelocity(-1.0f);
else if theEvent.Key = UPARROW AND theEvent.State = RELEASED
Entity.SetYVelocity(0.0f);
if theEvent.Key = LEFTARROW AND theEvent.State = PRESSED
Entity.SetXVelocity(-1.0f);
else if theEvent.Key = LEFTARROW AND theEvent.State = RELEASED
Entity.SetXVelocity(0.0f);
This way, if I have an XVelocity and I then press the UPARROW, I will still have my XVelocity, as well as a new YVelocity, thus moving diagonally.
Is there a better way? Am I missing something very simple here?
I am using SDL 1.2, OpenGL, C++. Not sure if there is something in SDL/OpenGL which would help?
Thanks in advance for your answers.
The question is really general since it depends on how you want to model the movement of your objects in your world.
Usually every object has its velocity which is calculated basing on an acceleration and capped to a maximum. This means that a key press alters the acceleration of the object for the specified frame which is then calculated and applied to the current velocity of the object.
This is done through an update phase which goes through all the objects and calculates the velocity change according to the object acceleration. In this way you don't bother to modify the velocity itself but you let your engine to do its calculations depending on the state of every object..
acceleration is applied over a period of time, so in the example by #jack, you would apply an acceleration 10m/s^2 over a time period of one second.
you should also modify your application to make it time based, not frame based.
have a look at this basic game physics introduction, and I would also really have a look at the GameDev.net Physics Tutorials
I assume the way you want movement to work is that you want the player to move only when a key is held.
In short: your solution is fine.
Some potential gotchas to take consideration of: What happens if both left and right is pressed?
Well, what you describe here is a simple finite state machine. You have the different directions in which you can move (plus no movement at all) as the states, and the key-events as transitions. This can usually be implemented quite well using the state pattern, but this is often quite painful in C++ (lots of boilerplate code), and might be over the top for your scenario.
There are of course other ways to represent speed and direction of your entity, e.g. as a 2D-vector (where the length gives the speed). This would enable you to easily represent arbitrary directions and velocities.