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mental.breakdance

Member Since 20 Mar 2012
Offline Last Active Sep 26 2012 04:46 PM

Topics I've Started

2D tile-based collision engine - ideas for improvement?

21 September 2012 - 10:33 PM

Hi all!

Just made a collision engine for my 2D tile based game, pieced together from what I've found/learnt from sites like this. Currently it works well enough, but I fear that with my limited testing, it's probably a bit buggy and not very well optimised. It may even be totally the wrong approach lol..

As such I thought I'd share it up for others to use & perhaps find ways to improve!

I'm using it for a platformer style game where each character has a collision rectangle, and the main thing that it does that may be a bit unorthodox is that they are allowed to 'step' up and down tiles depending on the height of the step (in tiles). This is because for my game, each tile is effectively a pixel of the level texture, and for ramps I don't want the character to have to jump up or fall down each pixel.

Things I already know about & haven't had the time to fix/implement:
  • [bug] there's definitely some issues with stepping down into gaps the same width as the rectangle (i.e. dropping too early)
  • [bug] the rectangle doesn't fit into holes the exact same width as it. They do however fit into holes the same height.
  • [bug/feature] Rectangles cannot 'step' down through zones the exact same height as themselves - i.e. if there is *just* enough room in a tunnel for the rectangle to get through, it would need to move down by itself rather than step - probably just a matter of not checking the top row of tiles when it is possible to step down..
  • [tidy] The 'Move' methods are almost exact duplicates of each other - I'm a bit OCD about avoiding code duplication and this irritates me Posted Image
  • [performance] It can probably be heavily optimised!
  • [possible bug] I haven't tested this in any tilesize other than (1f, 1f)...
Anyway, here it is:

public interface ITile
{
	bool Passable{ get; }
}

public interface ILevel
{
	Vector2 TileSize{ get; }
	ITile GetTileAt( int x, int y );
}

public class CollisionEngine : MonoBehaviour
{
	//TODO: null check all level tile access (could be out of range)
	public class CollisionResults
	{
		public bool CollidedX = false;
		public bool CollidedY = false;
	}
	private ILevel m_level = null;

	public CollisionEngine( Level level )
	{
		m_level = level;
	}
  
	private Vector2 UpdatePosition( Rect rect, Vector2 moveAmount, int maxStepAmount, out CollisionResults results )
	{
		Vector2 resultantPos = new Vector2( rect.x, rect.y );
		results = new CollisionResults();
		bool hasStepped = false;
		if( moveAmount.x != 0 )
		{
			int totalStepAmount = 0;
			int startMinY = GetRowIdx( rect.yMin, false );
			int startMaxY = GetRowIdx( rect.yMax, true );
			if( moveAmount.x < 0 ) // moving left
			{
				int startMinX = GetColumnIdx( rect.xMin, false );
				int endMinX = GetColumnIdx( rect.xMin + moveAmount.x, false );
				for( int x = startMinX; x > endMinX; --x )
				{
					float xDistThisIteration = (float)(x - startMinX) * m_level.TileSize.x;
					int steppedAmount;
					results.CollidedX = MoveLeft( GetColumnIdx( rect.xMin + xDistThisIteration, false ), // left
												  startMaxY, // top
												  GetColumnIdx( rect.xMax + xDistThisIteration, true ), // right
												  startMinY, // bottom
												  maxStepAmount,
												  out steppedAmount );
					if( results.CollidedX )
					{
						// can't move left
						resultantPos.x = (float)x * m_level.TileSize.x;
						break;
					}
					else
					{
						totalStepAmount += steppedAmount;
						startMinY += steppedAmount;
						startMaxY += steppedAmount;
					}
				}
			}
			else // moving right
			{
				int startMaxX = GetColumnIdx( rect.xMax, true );
				int endMaxX = GetColumnIdx( rect.xMax + moveAmount.x, true );
				for( int x = startMaxX; x < endMaxX; ++x )
				{
					float xDistThisIteration = (float)(x - startMaxX) * m_level.TileSize.x;
					int steppedAmount;
					results.CollidedX = MoveRight( GetColumnIdx( rect.xMin + xDistThisIteration, false ), // left
												   startMaxY, // top
												   GetColumnIdx( rect.xMax + xDistThisIteration, true ), // right
												   startMinY, // bottom
												   maxStepAmount,
												   out steppedAmount );
					if( results.CollidedX )
					{
						resultantPos.x = ((float)(x + 1) * m_level.TileSize.x) - rect.width;
						break;
					}
					else
					{
						totalStepAmount += steppedAmount;
						startMinY += steppedAmount;
						startMaxY += steppedAmount;
					}
				}
			}
			if( !results.CollidedX )
			{
				resultantPos.x = rect.xMin + moveAmount.x;
			}
			if( totalStepAmount != 0 )
			{
				resultantPos.y = Mathf.Floor( rect.yMin ) + ((float)(totalStepAmount) * m_level.TileSize.y);
				hasStepped = true;
			}
		}
		if( moveAmount.y != 0 &&
			!hasStepped )
		{
			int startMinX = GetColumnIdx( rect.xMin, false );
			int startMaxX = GetColumnIdx( rect.xMax, true );
			if( moveAmount.y < 0 ) // moving down
			{
				int startMinY = GetRowIdx( rect.yMin, false );
				int endMinY = GetRowIdx( rect.yMin + moveAmount.y, false );
				for( int y = startMinY; y > endMinY; --y )
				{
					float yDistThisIteration = (float)(y - startMinY) * m_level.TileSize.y;
					results.CollidedY = MoveDown( startMinX, // left
												  GetRowIdx( rect.yMax + yDistThisIteration, true ), // top
												  startMaxX, // right
												  GetRowIdx( rect.yMin + yDistThisIteration, false ) ); // bottom
					if( results.CollidedY )
					{
						// can't move down
						resultantPos.y = (float)y * m_level.TileSize.y;
						break;
					}
				}
			}
			else // moving up
			{
				int startMaxY = GetRowIdx( rect.yMax, true );
				int endMaxY = GetRowIdx( rect.yMax + moveAmount.y, true );
				for( int y = startMaxY; y < endMaxY; ++y )
				{
					float yDistThisIteration = (float)(y - startMaxY) * m_level.TileSize.y;
					results.CollidedY = MoveUp( startMinX, // left
												GetRowIdx( rect.yMax + yDistThisIteration, true ), // top
												startMaxX, // right
												GetRowIdx( rect.yMin + yDistThisIteration, false ) ); // bottom
					if( results.CollidedY )
					{
						// can't move up
						resultantPos.y = ((float)(y + 1) * m_level.TileSize.y) - rect.height;
						break;
					}
				}
			}
			if( !results.CollidedY )
			{
				resultantPos.y = rect.yMin + moveAmount.y;
			}
		}
		return resultantPos;
	}

	private bool MoveLeft( int left, int top, int right, int bottom, int maxStepAmount, out int steppedAmount )
	{
		bool collided = false;
		steppedAmount = 0;
		for( int y = bottom; y <= top; ++y )
		{
			if( !m_level.GetTileAt( left - 1, y ).Passable )
			{
				// try to step up the tiles if they're within stepping range
				if( y < bottom + maxStepAmount )
				{
					steppedAmount = y - bottom + 1;
				}
				else
				{
					collided = true;
					break;
				}
			}
		}
		if( !collided )
		{
			if( steppedAmount == 0 &&
				!m_level.GetTileAt( right + 1, bottom - 1 ).Passable ) // otherwise we would try to step down while completely airborne
			{
				// check if we can drop within stepping distance
				for( int yStep = 0; yStep < maxStepAmount + 1; ++yStep )
				{
					if( !MoveDown( left - 1, top - yStep, right - 1, bottom - yStep ) )
					{
						// if we're not on the last iteration (i.e. too far to step)
						if( yStep != maxStepAmount )
						{
							steppedAmount = -yStep - 1;
						}
						else
						{
							steppedAmount = 0;
						}
					}
				}
			}
			else
			{
				for( int yStep = 0; yStep < steppedAmount; ++yStep )
				{
					collided = MoveUp( left, top + yStep, right, bottom + yStep );
					if( collided )
					{
						steppedAmount = 0;
						break;
					}
				}
			}
		}
		return collided;
	}

	private bool MoveRight( int left, int top, int right, int bottom, int maxStepAmount, out int steppedAmount )
	{
		bool collided = false;
		steppedAmount = 0;
		for( int y = bottom; y <= top; ++y )
		{
			if( !m_level.GetTileAt( right + 1, y ).Passable )
			{
				// try to step up the tiles if they're within stepping range
				if( y < bottom + maxStepAmount )
				{
					steppedAmount = y - bottom + 1;
				}
				else
				{
					collided = true;
					break;
				}
			}
		}
		if( !collided )
		{
			if( steppedAmount == 0 &&
				!m_level.GetTileAt( left - 1, bottom - 1 ).Passable ) // otherwise we would try to step down while completely airborne
			{
				// check if we can drop within stepping distance
				for( int yStep = 0; yStep < maxStepAmount + 1; ++yStep )
				{
					if( !MoveDown( left + 1, top - yStep, right + 1, bottom - yStep ) )
					{
						// if we're not on the last iteration (i.e. too far to step)
						if( yStep != maxStepAmount )
						{
							steppedAmount = -yStep - 1;
						}
						else
						{
							steppedAmount = 0;
						}
					}
				}
			}
			else
			{
				for( int yStep = 0; yStep < steppedAmount; ++yStep )
				{
					collided = MoveUp( left, top + yStep, right, bottom + yStep );
					if( collided )
					{
						steppedAmount = 0;
						break;
					}
				}
			}
		}
		return collided;
	}

	private bool MoveUp( int left, int top, int right, int bottom )
	{
		bool collided = false;
		for( int x = left; x <= right; ++x )
		{
			if( !m_level.GetTileAt( x, top + 1 ).Passable )
			{
				collided = true;
				break;
			}
		}
		return collided;
	}

	private bool MoveDown( int left, int top, int right, int bottom )
	{
		bool collided = false;
		for( int x = left; x <= right; ++x )
		{
			if( !m_level.GetTileAt( x, bottom - 1 ).Passable )
			{
				collided = true;
				break;
			}
		}
		return collided;
	}

	/// <param name="roundDown">Return the left column index if we are perfectly between columns, as opposed to the right.</param>
	private int GetColumnIdx( float worldPosX, bool roundDown )
	{
		// cater for floating point inaccuracies - if we are aligned to a column we don't want to incorrectly position ourselves in the next one.
		float xf = worldPosX / m_level.TileSize.x;
		int xIdx;
		if( Mathf.Approximately( xf, Mathf.Round( xf ) ) )
		{
			xIdx = roundDown ? (Mathf.RoundToInt( xf ) - 1) : (Mathf.RoundToInt( xf ));
		}
		else
		{
			xIdx = Mathf.FloorToInt( xf );
		}
		return Mathf.Clamp( xIdx, 0, m_level.Columns - 1 );
	}

	/// <param name="roundDown">Return the lower row index if we are perfectly between columns, as opposed to the right.</param>
	private int GetRowIdx( float worldPosY, bool roundDown )
	{
		// cater for floating point inaccuracies - if we are aligned to a row we don't want to incorrectly position ourselves in the next one.
		float yf = worldPosY / m_level.TileSize.y;
		int yIdx;
		if( Mathf.Approximately( yf, Mathf.Round( yf ) ) )
		{
			yIdx = roundDown ? (Mathf.RoundToInt( yf ) - 1) : (Mathf.RoundToInt( yf ));
		}
		else
		{
			yIdx = Mathf.FloorToInt( yf );
		}
		return Mathf.Clamp( yIdx, 0, m_level.Rows - 1 );
	}
}

Any feedback welcome Posted Image

standing cross section verts on an arbitrary surface

20 March 2012 - 03:37 PM

Hi all,

Currently just confusing myself by trying to align things in 3D. I've discovered that describing my end goal is almost as hard as solving it, so here goes..

If I have an array of Vector2s that define the cross section of something I want to extrude along a path, how can I align that cross section to the normal of a surface? I.e. how do I work out the Vector3s that define the cross section as though it were 'coming out' of the surface? Assuming I give it a direction along the surface by which to point in..

Below is my code so far (which is blatantly wrong) - I'm wondering if I'm close to going about it the right way...


Vector3[] GetPoints( Vector3 surfaceNormal, Vector3 pointOnSurface, Vector3 directionAlongSurface, Vector2[] crossSectionVerts, Vector2 crossSectionOrigin )
{
	List<Vector3> vertices = new List<Vector3>();
	Quaternion startRotation = Quaternion.identity;
	Vector3 startDirection = Vector3.forward;
	if( surfaceNormal != Vector3.up )
	{
	   float startAngle = Vector3.Angle( Vector3.forward, surfaceNormal );
	   Vector3 startCross = ( surfaceNormal == Vector3.back ) ? Vector3.up : Vector3.Cross( Vector3.forward, surfaceNormal );
	   startRotation = Quaternion.AngleAxis( startAngle, startCross );
	   startDirection = startRotation * startDirection;
	}

	float angle = Vector3.Angle( startDirection, directionAlongSurface );
	Vector3 cross = ( directionAlongSurface == -startDirection ) ? surfaceNormal : Vector3.Cross( startDirection, directionAlongSurface );
	Quaternion rotation = Quaternion.AngleAxis( angle, surfaceNormal );

	for( int i = 0; i < crossSectionVerts.Length; ++i )
	{
	   vertices.Add( (rotation * startRotation * (crossSectionOrigin + crossSectionVerts[i])) + pointOnSurface );
	}
	return vertices.ToArray();
}


Cheers

PARTNERS