I'm having a glitch with this simple collision algorithm. I'm doing the rpg game tutorial from codingmadeeasy, and the collision is much alike any algorithm collision I've done in previous platformer style games. I've had this problem with previous games as well, just don't remember the fix. I have a map, it has lots of tiles, some are flagged as solid. their Update method checks for collision with the player.
If the tile is solid, it should stop the player and move him to a valid location.
Problem is when I go up or down, stick to the tile, and press a left or right movement key.
For example:
I'm pressing the Down key, I'm on top of the solid tile, and I press to go Left. at that moment, the player is relocated to to the Right of the tile.
This wouldn't happen if I go left or right and press up or down because of the if order in the collision method.
public void Update(GameTime gameTime, ref Player player)
{
if (State != TileState.Solid) return;
Rectangle tileRect =
new Rectangle((int)Position.X, (int)Position.Y,
SourceRect.Width, SourceRect.Height);
Rectangle playerRect =
new Rectangle((int)player.Sprite.position.X, (int)player.Sprite.position.Y,
player.Sprite.SourceRect.Width, player.Sprite.SourceRect.Height);
HandleCollisionWithTile(player, playerRect, tileRect);
}
/// <summary>
/// Repositions the player at the current position after collision with tile
/// </summary>
/// <param name="player">the player intersecting with the tile</param>
/// <param name="playerRect">the rectangle of the player</param>
/// <param name="tileRect">the rectangle of the tile</param>
private static void HandleCollisionWithTile(Player player, Rectangle playerRect, Rectangle tileRect)
{
// Make sure there's even collosion
if (!playerRect.Intersects(tileRect)) return;
// Left
if (player.Velocity.X < 0)
player.Sprite.position.X = tileRect.Right;
// Right
else if (player.Velocity.X > 0)
player.Sprite.position.X = tileRect.Left - player.Sprite.SourceRect.Width;
// Up
else if (player.Velocity.Y < 0)
player.Sprite.position.Y = tileRect.Bottom;
// Down
else if (player.Velocity.Y > 0)
player.Sprite.position.Y = tileRect.Top - player.Sprite.SourceRect.Height;
// Reset velocity
player.Velocity = Vector2.Zero;
}
Obviously, If I switch the two first ifs with the last, that would happen if I come from the side and press up or down.
What exactly am I missing?
As you've noted, this issue occurs because of the order in which you check the condition for collision. In particular, while visually your player sprite appears to be above a tile, your code is detecting the sprite as intersecting, and since the first check is for horizontal collisions, the player sprite's position is moved to the right of the tile's sprite (above and to the right, actually, so you only adjust the coordinate in the axis of the detected collision).
It seems to me that this exposes a fundamental flaw in the code: while one might argue that having resolved the collision that occurred in the vertical direction, by placing the player sprite at the top of the tile sprite, now the player sprite should not be in a collision state with the tile sprite, instead your code detects this condition as a collision.
Without a better code example, it's hard to know what the best fix might be. But an obvious quick-and-dirty solution would be to ensure that when you resolve a collision, you are not putting the player sprite in a position that intersects with the tile sprite. For example:
private static void HandleCollisionWithTile(Player player, Rectangle playerRect, Rectangle tileRect)
{
// Make sure there's even collosion
if (!playerRect.Intersects(tileRect)) return;
// Left
if (player.Velocity.X < 0)
player.Sprite.position.X = tileRect.Right + 1;
// Right
else if (player.Velocity.X > 0)
player.Sprite.position.X = tileRect.Left - player.Sprite.SourceRect.Width - 1;
// Up
else if (player.Velocity.Y < 0)
player.Sprite.position.Y = tileRect.Bottom + 1;
// Down
else if (player.Velocity.Y > 0)
player.Sprite.position.Y = tileRect.Top - player.Sprite.SourceRect.Height - 1;
// Reset velocity
player.Velocity = Vector2.Zero;
}
In other words, give yourself a 1 pixel margin around the tile into which the player sprite may not enter.
An alternative would be to "deflate" the tile rectangle (i.e. call Inflate() with negative values) by 1 pixel before checking for the intersection that defines a collision. Then when a collision does occur, the placement will be as before (i.e. without the +1 and -1 adjustments shown above), but that placement will not itself be detected as a collision.
There are many other ways to handle collision detection, but a) without more specifics about your scenario it's hard to know whether and which of those might be better choices, and b) given the apparently simple nature of your current implementation, a relatively simple fix as I've proposed above seems more likely to be warranted and useful.
Related
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.
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);
}
This is my code for the ball collision in arkanoid:
Rectangle intersection = Rectangle.Intersect(block.Rect2D, ball.BallRec);
if (intersection.Width > intersection.Height)
{
ball.yVel = -ball.yVel;
}
else if (intersection.Width < intersection.Height)
{
ball.xVel = -ball.xVel;
}
else
{
ball.xVel = -ball.xVel;
ball.yVel = -ball.yVel;
}
Unfortunately the ball sometimes "melts" into the blocks and bounces weirdly, especially when its at higher speed. How can I fix that?
When collision is detected it is not sufficient to just change the direction of the ball, you need to change the position too. If the ball moved 20 pixels, and is now 5 pixels into the block, then you need to move the ball 5 pixels away from the block.
You will also need to check if the block you are detecting collisions for was between the ball's old location and the new one.
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.
I have a simple rectangle-tile collision scheme set up, and it works beautifully.
The only problem is when you start falling off of a ledge. Your speed reaches the point where the change in Y/X each frame is large enough for you to clip into solid objects and glitch about.
Basically my setup is as follows:
To start with, the player's position has its velocity added to it, so the player is now at the place he would be next frame if no collisions happen.
The list below is just a single function, checkIntersectTiles(Vector2 maskPos);
Calculate tiles around the character to check.
Loop through tiles, including those inside the bounding tiles.
Check the player's collision rectangle against each of these tiles.
If there's an intersection, move the largest offending axis out of the tile, then set that axis velocity to 0.
Continue checks.
When you clip into the ground, you jitter around inside, as my algorithm attempts to move you outside the tile that is most colliding with you.
My solution: Check each position from the player's pos, to the player's pos + velocity.
I'm stuck on that bit.
Can anyone give me a hand?
I assume that your code to move the player out of the colliding tile does so in a single step. So if the player collides with a tile you determine that the penetration depth is 5 in the Y direction you immediately adjust the player Y position by -5.
As you suggest, check the player position at each step. So if the Y velocity is 5 then you can adjust the players Y position by 1, check for collision and then repeat 4 more times. See later for calculations handling time stepping. The following is just some basic pseudo code and just in the Y direction.
player.Y += vel;
if (player.CheckCollisions())
{
// handle collision
}
Becomes
for (int i = 0; i < vel; ++i)
{
player.Y += 1;
if (player.CheckCollisions())
{
// handle collision
break;
}
}
That is the simple version if you are not adjusting for ellaped time. If you are, then you rather perform smaller time steps
So
player.Y += vel * elapsedTime;
if (player.CheckCollisions())
{
// handle collision
}
Becomes
float currentTimeStep = 0;
Position startY = player.Y;
while (currentTimeStep < elapsedTime)
{
currentTimeStep = Math.Min(currentTimeStep + stepDelta, elapsedTime); // You need to tune the stepDelta
player.Y = startY + vel * currentTimeStep;
if (player.CheckCollisions())
{
// handle collision
break;
}
}
In the above you will need to tune the time step delta to ensure that you balance performance with accuracy. You might event consider calculating the delta dynamically each frame to ensure that the adjustment is close to 1 pixel.