gistfile1.cs

...
    private Vector2 ApplyTileCollision(Vector2 deltaVelocity)
    {
        var deltaPosition = this.Position + deltaVelocity;

        // Reset active values, as they are recalculated.
        this.ActiveFriction = Single.NaN;
        this.ActiveElasticity = Single.NaN;

        var startx = this.TileStartX - 1;
        var endx = this.TileEndX + 1;
        var starty = this.TileStartY - 1;
        var endy = this.TileEndY + 1;

        TileRegion? horizontalWall = null;
        TileRegion? verticalWall = null;

        if (this.IsMovingRight)
        {
            // Make a wall to the right of the entity.
            verticalWall = this.realm.GetTileRegion(endx, starty + 1, endx, endy - 1);
        }
        else if (this.IsMovingLeft)
        {
            // Make a wall to the left of the entity.
            verticalWall = this.realm.GetTileRegion(startx, starty + 1, startx, endy - 1);
        }

        if (this.IsMovingDown)
        {
            // Make a floor under the entity.
            horizontalWall = this.realm.GetTileRegion(startx + 1, endy, endx - 1, endy);
        }
        else if (this.IsMovingUp)
        {
            // Make a ceiling above the entity.
            horizontalWall = this.realm.GetTileRegion(startx + 1, starty, endx - 1, starty);
        }

        // Reset horizontal flags.
        this.IsPushingLeft = false;
        this.IsPushingRight = false;
        if (verticalWall.HasValue && verticalWall.Value.IsSolid)
        {
            if (this.IsMovingRight && deltaPosition.X + this.Width >= verticalWall.Value.BoundingBox.Left)
            {
                this.IsPushingRight = true;
                deltaVelocity.X = verticalWall.Value.BoundingBox.Left - this.Right - 1.00f;
            }
            else if (this.IsMovingLeft && deltaPosition.X < verticalWall.Value.BoundingBox.Right)
            {
                this.IsPushingLeft = true;
                deltaVelocity.X = verticalWall.Value.BoundingBox.Right - this.Left;
            }
        }

        // Reset vertical flags.
        this.IsPushingDown = false;
        this.IsPushingUp = false;
        if (horizontalWall.HasValue && horizontalWall.Value.IsSolid)
        {
            if (this.IsMovingDown && deltaPosition.Y + this.Height >= horizontalWall.Value.BoundingBox.Top)
            {
                this.ActiveFriction = horizontalWall.Value.Friction;
                this.IsPushingDown = true;
                if (deltaVelocity.Y > 4.00f)
                {
                    this.ActiveElasticity = horizontalWall.Value.Elasticity;
                    deltaVelocity.Y = horizontalWall.Value.BoundingBox.Top - this.Bottom - 1.00f;
                }
                else
                {
                    deltaVelocity.Y = horizontalWall.Value.BoundingBox.Top - this.Bottom - 1.00f;
                }
            }
            else if (this.IsMovingUp && deltaPosition.Y < horizontalWall.Value.BoundingBox.Bottom)
            {
                this.IsPushingUp = true;
                deltaVelocity.Y = horizontalWall.Value.BoundingBox.Bottom - this.Top;
            }
        }

        return deltaVelocity;
    }
...