XNA: check collision on list of bricks - c#

I am having a big struggle implementing a collision detect on a list of bricks.
I have a game which randomly drops bricks that are supposed to stack up at the bottom of the screen. I managed to make them stop at the bottom of the screen but they don't stack.
I have this in my update function:
if (r.Next(0, 50) == 8)
{
_bricks.Add(new NormalBrick(this, new Vector2(r.Next(0, 700), 100)));
}
foreach(Brick b in _bricks)
{
b.move(GraphicsDevice.Viewport);
}
My move() function has the following code:
public void move(Viewport viewport)
{
if (_position.Y == (viewport.Height - _texture.Height ))
{
_position = new Vector2(_position.X, _position.Y);
}
else
{
_position = new Vector2(_position.X, _position.Y + _speed);
}
}
How can I make sure that the bricks don't all stop at the bottom of the screen, instead the brick has to check if there is a brick beneath it?
I have checked other questions on here but I couldn't find my answer and I have tried several things to get it fixed. Any help would be appreciated.

I would create Rectangles for each of your Bricks (unless you have already done so). Then in the Update() method, use something like brick.Rectangle.Intersects(anotherBrick) after movement. If true, then position the current brick above the intersecting bottom brick.
Make sure to move the brick's rectangle each time the brick moves.
I hope this helps. Let me know if you require any further assistance.

Related

Detection of 2d collision side behaving weird

I am making a basic Breakout game and using the following code to detect if the collision between the Capsule Collider 2d and circle collider 2d has happened on the top:
bool FindIfTopCol(Collision2D other)
{
print("collider.y " + collidersize.y / 2);
ContactPoint2D[] contacts = other.contacts;
if (contacts[0].point.y - transform.position.y > collidersize.y / 2)
{
print("top " + (contacts[0].point.y - transform.position.y));
return true;
}
else
{
print("not top " + (contacts[0].point.y - transform.position.y));
return false;
}
}
For the most part the detection was working fine but after running the game a while and especially after the circle collider gets into a non top collision, the method seems to return all the collisions as non top collision.
To figure out the issue i placed print statements and this is the result:
collidery 0.2610874
top 0.2885695
collidery 0.2610874
not top 0.2552783 First actual non top collision
collidery 0.2610874
not top 0.2542975 It's a top collision, but shows as not top
collidery 0.2610874
not top 0.2558844 It's top collision, but shows as not top
And the rest of the collisions for the session is also wrong like this, until i restart the game.
I am not sure whats going wrong here.
And also if there is a better way to detect collision side, please let me know.
I'm not really sure what's happening here but I would use OnCollisionEnter2D() event to detect collisions. Then compare the contact point with the collider center to figure out what surface it hit. Here's an example from kacyesp.
Vector3 contactPoint = collision.contacts[0].point;
Vector3 center = collider.bounds.center;
bool right = contactPoint.x > center.x;
bool top = contactPoint.y > center.y;

Mouse drag direction tolerance

I'm working on a 2D game where the player can drag tiles around. It works in a way that the player clicks and hold a tile and depending in which direction the player moves the mouse from then on, the drag direction is decided.
The problem however is that this is overly sensitive. It might often be the case that the player starts dragging and wanted to drag vertically but due to the mouse sensitivity it turns out to drag horizontally (or vice versa).
Does anyone have an idea how to add a tolerance threshold to this dragging behavior? The relevant part in my code looks basically like this:
private void Update()
{
if (_isMouseDown && sourceTile != null)
{
_isDraggingTile = true;
/* Determine drag direction and drag target cell. */
Vector3 dragDistance = Input.mousePosition - _originMousePosition;
dragDistance.Normalize();
if (_dragDirection == DragDirection.None)
{
float f = Vector3.Dot(dragDistance, Vector3.up);
/* Mouse up drag. */
if (f >= 0.5f)
{
_dragDirection = DragDirection.Up;
_dragTargetCell = sourceTile.gridCell.upNeighbor;
}
/* Mouse down drag. */
else if (f <= -0.5f)
{
_dragDirection = DragDirection.Down;
_dragTargetCell = sourceTile.gridCell.downNeighbor;
}
else
{
/* Mouse right drag. */
f = Vector3.Dot(dragDistance, Vector3.right);
if (f >= 0.5f)
{
_dragDirection = DragDirection.Right;
_dragTargetCell = sourceTile.gridCell.rightNeighbor;
}
/* Mouse left drag. */
else if (f < -0.5f)
{
_dragDirection = DragDirection.Left;
_dragTargetCell = sourceTile.gridCell.leftNeighbor;
}
}
}
if (_dragTargetCell != null)
{
// Take care of moving the dragged tile!
}
}
}
Simply delaying the calculation of dragDistance by some frames doesn't turn out to work very well. I think what is needed is a solution to figure out the mouse movement and decide on which axes it moves farthest. Determining the drag direction as above will probably never work out well.
The problem with any collection of information is noise. In your case, the noise is defined by the wrong movement of the user. Nonetheless, it should be possible to minimize the effect of noise by averaging the values.
There are advanced algorithms used in DSP but I guess a basic averaging of the info should do in your case.
What you could try is that instead of moving in Update at once like you do, collect movement over several frames, then average all those frames and see if it goes better:
IEnumerator GetAverageMovement(Action<Vector3> result)
{
int frames = 0;
List<Vector3>list = new List<Vector3>();
while(frames < 30f) // half a second appr
{
list.Add(GetDirection());
frames++;
yield return null;
}
result(AverageAllValues());
}
GetDirection is just returning the delta between current and previous position, AverageAllValues simply adds all values in list and divides by list.Count (aka 30).
This should fix cases when the user move all the way right but a bit up at the end. The last bit should be canceled by the large right movement.
If that is still not enough, then you could add some logic within the method that if a value is too far gone from the average, discard it. I don't think you need this in there.
I think you should create a Queue of positions with limited size right after dragging .
by comparing final value of Queue and first value you can find the direction.
If you want to get better results you can get Variance of positions and get better results.

Collision with walls does not apply when changing ball location

I've been working on a Breakout-style project recently and wanted to make it so that once a user enters the 'cheat mode', they'll be able to move the ball in their desired direction.
Here's what my code looks like: https://gist.github.com/anonymous/7589f4f141888c3c32c7
I've included the return; in my ball class due to the fact that if I don't, the program will not recognise the changes in the X and Y. So basically, my problem is, I want the program to ignore the existing x and y speeds and use the ones provided by the user if the cheat mode is enabled. (Meaning if the user enters the cheat mode, the program should stop the ball where it last was, in terms of x and y coordinates, and let the user move it)
Example of what I mean:
Player enters cheat mode -> Presses Up.
- Ball keeps moving up until it hits the top of the form and then should bounce back in the opposite direction to which it hit the wall.
How do I implement this into my program? I used the 'if statement' for the boolean cheat mode and the return function to exit the moveBall procedure (which ignores the xSpeed and ySpeed but ultimately stops the ball from moving on it's own completely, so the player has to keep clicking Up to move the ball up, otherwise it stays in place.
EDIT:
Okay, I've fixed the issue where the ball wouldn't move, I just added a few more variables for the X and Y change of the ball.
Here's what my code looks like now:
public void moveBall()
{
if (Form1.cheatModeClicked == true)
{
ballRec.X += cheatX;
ballRec.Y -= cheatY;
}
else
{
ballRec.X += xSpeed;
ballRec.Y -= ySpeed;
}
}
However, the ball collision still doesn't want to work, and I don't know why?
It sounds like you need to add a method to the ball class to allow the ball's speed to be set externally. Then you can call that method when keys are pressed, depending on the cheat mode state. The cheat mode state should be stored outside the ball class anyway. The ball itself should only know about ball things and not what a non-ball concept such as cheat mode is.
Here is some pseudo code, I might have missed a few things in the description but hopefully it helps
class Form
{
bool _inCheatMode = false;
Ball ball;
void EnterCheatMode()
{
_inCheatMode = true;
ball.SetSpeed(0, 0); //stop the ball
}
void ExitCheatMode()
{
_inCheatMode = false;
}
void KeyDown(Keys key)
{
if (_inCheatMode)
{
if (key == Keys.Up)
ball.SetSpeed(0, -1);
}
}
}
class Ball
{
public void SetSpeed(x, y)
{
}
}

How to determine which side of a rectangle collides with a circle

Before you point out that there are other answers to this question, i have looked at if not all, most of the other answers to this question or a similar question and i haven't found the solution i require.
Basically all i want to be able to do is when the circle/ball collides with a rectangle, i want to determine which side of the rectangle this collision has occured at. I want to find this out so that i can enforce a bit more realistic physics, e.g. if the ball hits the top of the rectangle, inverse it's Y velocity only... instead of both.
I have tried comparing the X and Y positions of the ball and the rectangle and even the location of both of their bounding boxes... testing even if the bottom of the ball's box has intersected with the rectangles top... using 'if ball.boundingBox.Bottom >= rectangle.boundingBox.Top'.
I have attached a picture to this to show what i am trying to achieve... just in case it's a bit confusing, as it's not detailed... the red what look like v's is the path if the ball comes in from one side, i want the movement upon impact to travel in the opposite way but this depends on the side of the rectangle as to what component of the ball's velocity i will have to change...
FYI i have also looked at vector normalisation... i haven't used it before so forgive me if this could be solved using this...
Thanks v.much for reading
EDIT as i am in a rush, i have used an different image instead... this still shows the behaviour i am trying to achieve, as the physics shown on the diagram is how i want the ball to behave when it collides with the other sides...
LINK TO IMAGE: http://codeincomplete.com/posts/2011/6/12/collision_detection_in_breakout/bounce2.v283.png
This code might be more comprehensive than you need and can be refactored to suit your needs but it is a complete answer and is flexible to use with moving bounding rectangles along with moving circles.
here is a graphic to give a visual aid to what the code is doing.
the red circle is intersecting with the black rectangle. visualize two imaginary lines going through opposite corners. If you know which side of each of the 2 lines the circle is on, you can deduce the collided edge.
first declare class scope private members
Rectangle CollisionBoxRect;
Rectangle circleRect;
Dictionary<string, Vector2> corners;
In your update after you've moved the circle and set its location and the potential intersected box's location it does a basic check to see if the circle's bounding rect is involved with the block's bounding rect. If so, it then alters the ball's velocity with the appropriate collision normal depending on which side of the rect the circle collided with.
if (CollisionBoxRect.Intersects(circleRect))
{
ballVelocity = Vector2.Reflect(ballVelocity, GetCollisionNormal(CollisionBoxRect));
}
The following methods support getting the proper side (the normal actually). Some of these methods can be done once in the initialize phase if they never change (like the get corners method);
private Vector2 GetCollisionNormal(Rectangle boxBeingIntersected)
{
getCorners(boxBeingIntersected);
bool isAboveAC = isOnUpperSideOfLine(corners["bottomRight"], corners["topLeft"], getBallCenter());
bool isAboveDB = isOnUpperSideOfLine( corners["topRight"], corners["bottomLeft"], getBallCenter());
if (isAboveAC)
{
if (isAboveDB)
{
//top edge has intersected
return -Vector2.UnitY;
}
else
{
//right edge intersected
return Vector2.UnitX;
}
}
else
{
if (isAboveDB)
{
//left edge has intersected
return -Vector2.UnitX;
}
else
{
//bottom edge intersected
return Vector2.UnitY;
}
}
}
public bool isOnUpperSideOfLine(Vector2 corner1, Vector2 oppositeCorner, Vector2 ballCenter)
{
return ((oppositeCorner.X - corner1.X) * (ballCenter.Y - corner1.Y) - (oppositeCorner.Y - corner1.Y) * (ballCenter.X - corner1.X)) > 0;
}
private Vector2 getBallCenter()
{
return new Vector2(circleRect.Location.X + circleRect.Width / 2, circleRect.Location.Y + circleRect.Height / 2);
}
private void getCorners(Rectangle boxToGetFrom)
{
corners.Clear();
Vector2 tl = new Vector2(boxToGetFrom.X, boxToGetFrom.Y);
Vector2 tr = new Vector2(boxToGetFrom.X + boxToGetFrom.Width, boxToGetFrom.Y);
Vector2 br = new Vector2(boxToGetFrom.X + boxToGetFrom.Width, boxToGetFrom.Y + boxToGetFrom.Height);
Vector2 bl = new Vector2(boxToGetFrom.X, boxToGetFrom.Y + boxToGetFrom.Height);
corners.Add("topLeft", tl);
corners.Add("topRight", tr);
corners.Add("bottomRight", br);
corners.Add("bottomLeft", bl);
}

Tile Engine Collision

Okay, so, I am making a small tile-based digging game, now I want to do collision. How would I go about doing this correctly? I know how to check if the player collides with a tile, but I don't know how to actually make the player stop when it hits a wall.
This is the game, I got 20x20 tiles here.
This is the code I'm using atm:
foreach (Tile tiles in allTiles)
{
if (ply.rect.Intersects(tiles.rect))
{
if (tiles.ID != -1 && tiles.ID != 1)
{
if (ply.X > tiles.X)
{
Console.WriteLine("Right part.");
ply.X = tiles.pos.X + 30;
}
if (ply.X <= tiles.X)
{
Console.WriteLine("Left part.");
ply.X = tiles.pos.X - 30;
}
if (ply.Y > tiles.Y)
{
Console.WriteLine("Bottom part.");
ply.Y = tiles.pos.Y + 30;
}
if (ply.Y <= tiles.Y)
{
Console.WriteLine("Upper part.");
ply.Y = tiles.pos.Y - 30;
}
}
}
}
What type of collision detection are you using?
If your using Rectangles and the '.intersects' method you can always declare a bool to make sure your character is touching the floor. If he isn't you apply a Gravity Vector to make it fall to the next Tile with a different Rectangle so when he hits it he's going to stop falling.
If you want to block him from side to side just test to see which side of the rectangle he is touching and block him from moving on the 'X' axis.
E.g if he is going right and intersects with the left part of a rectangle, block is 'GoingRight' movement.
if(myCharacterRectangle.Intersects(tileRectangle)
{
if(myCharacterPosition.X > (tilePosition.X)
{
//You know the character hits the Right part of the tile.
}
if(mycharacterPosition.X <= tilePosition.X)
{
//You know the character hits the Left Part of the tile.
}
}
And same goes for the Position.Y if you want to test the Top or Bottom.
If you want to use Pixel by Pixel collision detection using Matrices I know a good tutorial here.
The detection will return a 'Vector2(-1,-1)' if there is no collision.
If there is a one the method will return the coordinates of the collisions which makes it even easier to determine what part of the tile your character is touching.
Hope this helps. Good Luck with your game.

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