Collision Detection, player correction
- by DoomStone
I am having some problems with collision detection, I have 2 types of objects excluding the player. Tiles and what I call MapObjects. The tiles are all 16x16, where the MapObjects can be any size, but in my case they are all 16x16. When my player runs along the mapobjects or tiles, it get verry jaggy. The player is unable to move right, and will get warped forward when moving left. I have found the problem, and that is my collision detection will move the player left/right if colliding the object from the side, and up/down if collision from up/down.
Now imagine that my player is sitting on 2 tiles, at (10,12) and (11,12), and the player is mostly standing on the (11,12) tile. The collision detection will first run on then (10,12) tile, it calculates the collision depth, and finds that is is a collision from the side, and therefore move the object to the right. After, it will do the collision detection with (11,12) and it will move the character up. So the player will not fall down, but are unable to move right. And when moving left, the same problem will make the player warp forward.
This problem have been bugging me for a few days now, and I just can't find a solution!
Here is my code that does the collision detection.
public void ApplyObjectCollision(IPhysicsObject obj, List<IComponent> mapObjects, TileMap map)
{
PhysicsVariables physicsVars = GetPhysicsVariables();
Rectangle bounds = ((IComponent)obj).GetBound();
int leftTile = (int)Math.Floor((float)bounds.Left / map.GetTileSize());
int rightTile = (int)Math.Ceiling(((float)bounds.Right / map.GetTileSize())) - 1;
int topTile = (int)Math.Floor((float)bounds.Top / map.GetTileSize());
int bottomTile = (int)Math.Ceiling(((float)bounds.Bottom / map.GetTileSize())) - 1;
// Reset flag to search for ground collision.
obj.IsOnGround = false;
// For each potentially colliding tile,
for (int y = topTile; y <= bottomTile; ++y)
{
for (int x = leftTile; x <= rightTile; ++x)
{
IComponent tile = map.Get(x, y);
if (tile != null)
{
bounds = HandelCollision(obj, tile, bounds, physicsVars);
}
}
}
// Handel collision for all Moving objects
foreach (IComponent mo in mapObjects)
{
if (mo == obj)
continue;
if (mo.GetBound().Intersects(((IComponent)obj).GetBound()))
{
bounds = HandelCollision(obj, mo, bounds, physicsVars);
}
}
}
private Rectangle HandelCollision(IPhysicsObject obj, IComponent objb, Rectangle bounds, PhysicsVaraibales physicsVars)
{
// If this tile is collidable,
SpriteCollision collision = ((IComponent)objb).GetCollisionType();
if (collision != SpriteCollision.Passable)
{
// Determine collision depth (with direction) and magnitude.
Rectangle tileBounds = ((IComponent)objb).GetBound();
Vector2 depth = bounds.GetIntersectionDepth(tileBounds);
if (depth != Vector2.Zero)
{
float absDepthX = Math.Abs(depth.X);
float absDepthY = Math.Abs(depth.Y);
// Resolve the collision along the shallow axis.
if (absDepthY <= absDepthX || collision == SpriteCollision.Platform)
{
// If we crossed the top of a tile, we are on the ground.
if (obj.PreviousBound.Bottom <= tileBounds.Top)
obj.IsOnGround = true;
// Ignore platforms, unless we are on the ground.
if (collision == SpriteCollision.Impassable || obj.IsOnGround)
{
// Resolve the collision along the Y axis.
((IComponent)obj).Position = new Vector2(((IComponent)obj).Position.X, ((IComponent)obj).Position.Y + depth.Y);
// If we hit something about us, remove all velosity upwards
if (depth.Y > 0 && obj.IsJumping)
{
obj.Velocity = new Vector2(obj.Velocity.X, 0);
obj.JumpTime = physicsVars.MaxJumpTime;
}
// Perform further collisions with the new bounds.
return ((IComponent)obj).GetBound();
}
}
else if (collision == SpriteCollision.Impassable) // Ignore platforms.
{
// Resolve the collision along the X axis.
((IComponent)obj).Position = new Vector2(((IComponent)obj).Position.X + depth.X, ((IComponent)obj).Position.Y);
// Perform further collisions with the new bounds.
return ((IComponent)obj).GetBound();
}
}
}
return bounds;
}
Update: I have uploaded the source code, if you want to look that through. I think that my general approach might be wrong when i am working with small tiles, I have also be unable to find any good information on physics and collision detection in Platform games.
http://dl.dropbox.com/u/3181816/Sogaard.Games.SuperMario.rar
