I am developing a XNA based 2D-game for Windows Phone 7.1. My requirement is to flick an object, based on the amount and angle of flick, it will animate in a vertical projectile motion. For e.g. there is a lake infront of you, and you want to throw a stone into it. The same motion has to be replicated with camera being human's eye.
There are 3 levels of distance to be covered. The distance covered in Y-axis is more than the distance covered in X-axis.
I could see many equations given for projectile motion in horizontal (X-) axis but none to show projectile motion in Y-axis.
Any idea how to achieve this projectile motion in terms of X- and Y- coordinates?
If you use a Vector2 instead of an angle, you can implement a very rudimentary physics engine which will be simple and accurate.
The object to be flicked will have a Vector2 Velocity and a Vector2 Position.
Then you can just add the distance between the mouse as a Vector2 to the Velocity, and add the Velocity to the Position every frame, and then add gravity.
Here is a sample implementation:
public class FlickObject
{
public Vector2 Velocity;
public Vector2 Position;
public FlickObject () {}
public void Update(GameTime t)
{
Position += Velocity;
}
}
And in the game class (when the user flicks the object):
flickObject.Velocity += FlickDistance;
Where FlickDistance is the distance between the mouse (or however you calculate it) and the object.
To finish it off, add gravity:
flickObject.Velocity += new Vector2(0, GRAVITY);
Where GRAVITY is set to some positive value.
Related
I have a particle engine which creates an emitter at my mouse position.
particleEngine.EmitterLocation = new Vector2(Mouse.GetState().X, Mouse.GetState().Y);
It's in the Update method in Game1.cs.
I have another class which is called Ball.cs with its bouncing physics, and Texture2D texture; Vector2 position.
Now how do I make the emitter / particles follow the ball instead?
pass a reference to the particleEngine to the Ball class and set the EmitterLocation to the ball's location.
Example:
Game1, Initialize (for instance):
ParticleEngine particleEngine = new ParticleEngine();
Ball ball = new Ball(particleEngine);
In the Ball class:
class Ball
{
ParticleEngine particleEngine;
Vector2 position;
public Ball(ParticleEngine particleEngine)
{
this.particleEngine = particleEngine;
}
public void Update(GameTime gameTime)
{
//Update position
particleEngine.EmitterLocation = new Vector2(this.position.X, this.position.Y);
}
}
I don't know how your particle engine works or anything about your code structure, but with the information given I did my best to implement an understandable example.
I made a 2D isometric renderer. It works fine but now I want to show my scene from 4 differents point of view (NO NW SE SW) but, on a 90° rotation, my camera cannot keep the center of my scene on screen.
What's working :
I calcul new projection of scene to match the new viewport (x y z in my world).
I reorganise part of my scene(chunk) to draw them in a correct order
I reorganise 'tiles' of 'chunks' to draw them in a correct order
I can keep the correct center with a 180 degres rotation.
What's do not working :
I cannot find a correct translation to apply to my camera after a 90 degres rotation.
What I know :
To keep the same center on a 180° rotation with my camera I have to do this :
camera.Position -= new Vector2(2 * camera.Position.X + camera.Width, 2 * camera.Position.Y + camera.Height);
Illustration
If the center of your map is origo (0,0,0), this gets easy:
First you store your default camera position in a Vector3 CameraOffset, then you calculate position using a rotation-matrix. 90* in redians is half a Pi, so we will use PiOverTwo. We will also use an enum to decide what direction to be pointing, so you can say
Camera.Orientation = Orientation.East;
and the camera should fix itself :)
public enum Orientation
{
North, East, South, West
}
in camera:
public Vector3 Position { get; protected set; }
Vector3 _CameraOffset = new Vector3(0, 20, 20);
public Vector3 CameraOffset
{
get
{
return _Orientation;
}
set
{
_Orientation = value;
UpdateOrientation();
}
}
Orientation _Orientation = Orientation.North;
public Orientation Orientation
{
get
{
return _Orientation;
}
set
{
_Orientation = value;
UpdateOrientation();
}
}
private void UpdateOrientation()
{
Position = Vector3.Transform(CameraOffset, Matrix.CreateRotationY(MathHelper.PiOverTwo * (int)Orientation));
}
If you want a gliding movement between positions, I think I can help too ;)
If your camera does not focus on Vector3.Zero and should not rotate around it, you just need to change:
Position = Vector3.Transform(CameraOffset, Matrix.CreateRotationY(MathHelper.PiOverTwo * (int)Orientation));
to:
Position = Vector3.Transform(CameraOffset, Matrix.CreateRotationY(MathHelper.PiOverTwo * (int)Orientation) * Matrix.CreateTranslation(FocusPoint));
Here, FocusPoint is the point in 3D that you rotate around (your worlds center). And now you also know how to let your camera move around, if you call UpdateOrientation() in your Camera.Update() ;)
EDIT; So sorry, totally missed the point that you use 2D. I'll be back later to see if I can help :P
I am really looking to try to have gravity in my game. I know everyone says use Box2D, but in my case I can't. I need to use Cocos2D for the gravity.
I know Cocos2D does not have any gravity API built in so I need to do something manually. The thing is there is like no tutorials or examples anywhere on the web that show this.
Can anyone show me what they have done or can some explain step by step on how to apply a non-constant gravity (One that gets slightly stronger while falling).
I think this will help a lot of people that are facing the same issue that I am having!
Thanks!
Gravity is nothing but a constant velocity applied to the body for every physics step. Have a look at this exemplary update method:
-(void) update:(ccTime)delta
{
// use a gravity velocity that "feels good" for your app
const CGPoint gravity = CGPointMake(0, -0.2);
// update sprite position after applying downward gravity velocity
CGPoint pos = sprite.position;
pos.y += gravity.y;
sprite.position = pos;
}
Every frame the sprite y position will be decreased. That's the simple approach. For a more realistic effect you will want to have a velocity vector for each moving object, and apply gravity to the velocity (which is also a CGPoint).
-(void) update:(ccTime)delta
{
// use a gravity velocity that "feels good" for your app
const CGPoint gravity = CGPointMake(0, -0.2);
// update velocity with gravitational influence
velocity.y += gravity.y;
// update sprite position with velocity
CGPoint pos = sprite.position;
pos.y += velocity.y;
sprite.position = pos;
}
This has the effect that velocity, over time, increases in the downward y direction. This will have the object accelerate faster and faster downwards, the longer it is "falling".
Yet by modifying velocity you can still change the general direction of the object. For instance to make the character jump you could set velocity.y = 2.0 and it would move upwards and come back down again due to the effect of gravity applied over time.
This is still a simplified approach but very common in games that don't use a "real" physics engine.
Ok so I have a ship which moves up and down based on the axis regardless of where the ship is facing.
How do I make the ship move in the direction it's facing? i.e. if my ship is facing east, key up makes it go north rather than east.
Your question isn't very clear - I will assume you're using models and matrices (as opposed to SpriteBatch or something else). So, making a guess - I'd say that the order of your matrix operations is incorrect.
This answer to a similar question may help.
Each matrix operation happens around the origin. So if you're doing your rotation after you move your ship into position, your rotation will also effectively "rotate" the direction of movement.
The easiest way is to make an angle and velocity variable so when you click left and right you change the angle and when you click up and down you changle the speed of your ship.
KeyboardState ks;
float speed = 0;
float angle = 0;
protected override void Update(GameTime gameTime)
{
ks = Keyboard.GetState();
if(ks.IsKeyDown(Keys.Up)) speed += 10;
if (ks.IsKeyDown(Keys.Down)) speed -= 10;
if (ks.IsKeyDown(Keys.Right)) angle += 10;
if (ks.IsKeyDown(Keys.Left)) angle -= 10;
}
You need to have direction vector like this
Vector3 direction = Vector3.Transform(Vector3.Forward, Matrix.CreateFromYawPitchRoll(yaw, pitch, roll));
Next, get your velocity vector
Vector3 velocity = direction * speed;
And move your ship
float time (float) = gameTime.ElapsedTime.TotalSeconds;
position += velocity * time;
In this example yaw is angle, pitch and roll keep 0.
Im doing some practices on XNA, and i created a class that represents a Camera.
My objective is that when the user press some keys make a translation of the camera (not the target) 90 degrees in the X axys (to see an object that i placed in the scene from different angles). By the moment i move the camera in X, Y, and Z without problems.
Actually to set up my camera i use the following lines of code:
public void SetUpCamera()
{
#region ## SET DEFAULTS ##
this.FieldOfViewAngle = 45.0f;
this.AspectRatio =1f;
this.NearPlane = 1.0f;
this.FarPlane = 10000.0f;
#endregion
this.ProjectionMatrix = Matrix.CreatePerspectiveFieldOfView(MathHelper.ToRadians(this.FieldOfViewAngle), 16 / 9, this.NearPlane, this.FarPlane);
this.ViewMatrix = Matrix.CreateLookAt(new Vector3(this.PositionX, this.PositionY, this.PositionZ), new Vector3(this.TargetX, this.TargetY, this.TargetZ), Vector3.Up);
}
I have this method to move the camera:
public void UpdateView()
{
this.ViewMatrix = Matrix.CreateLookAt(new Vector3(this.PositionX, this.PositionY, this.PositionZ), new Vector3(this.TargetX, this.TargetY, this.TargetZ), Vector3.Up);
}
Then in the game (update event handler i have the following code)
if (keyboardstate.IsKeyDown(Keys.NumPad9))
{
this.GameCamera.PositionZ -= 1.0f;
}
if (keyboardstate.IsKeyDown(Keys.NumPad3))
{
this.GameCamera.PositionZ += 1.0f;
}
this.GameCamera.UpdateView();
I would like to know how to make this camera translation of 90 degrees to surround one object that i placed in the screen.
To explain my self better about the camera movement here is a video on youtube that uses the exact movement that im trying to describe (see from 14 second)
http://www.youtube.com/watch?v=19mbKZ0I5u4
Assuming the camera in the video is orbiting the car, here is how you would accomplish that in XNA.
For the sake of readability, we'll just use vectors instead of their individual components. So 'target' means it's a Vector3 that includes TargetX, TargetY, & TargetZ. Same with the camera’s position. You can break X, Y, Z values out into fields and make Vector3s out of them to plug into this code if you want to later, but really it would be best for you to work at vector level instead of component level.
//To orbit the car (target)
cameraPosition = Vector3.Transform(cameraPosition – target, Matrix.CreateRotationY(0.01f)) + target;
this.ViewMatrix = Matrix.CreateLookAt(cameraPosition, target, Vector3.Up);
Since all matrix rotations act about an axis that intersects the world origin, to use a rotation matrix to rotate the camera around the car, the object of rotation has to be shifted such that the target (and thus the rotation axis) is located at the world origin. CameraPosition - target accomplishes that. Now cameraPosition can be rotated a little bit. Once cameraPosition is rotated a little bit, it needs to be sent back to the scene at hand, that's what the '+ target' at the end of the line is for.
The 0.01f can be adjusted to whatever rotation rate suits you.