Question

I have a problem finding out if two PolyLines intersect.

Well the main objective is to compare last X and Y with the other PolyLine and find out if it’s colliding aka intersecting with it.

There are gaps in the data due moving the X and Y, so most of the time I can’t find the X and Y in the other PolyLine.

I think I should compare the visualtree or something and not the data itself, but I have no idea how to get do that.

<Canvas x:Name="LayoutRoot" Background="Black" Margin="2">
    <Polyline x:Name="player3line" Stroke="GreenYellow" StrokeThickness="4" Points="146,106 141,106 136,105 131,105 126,105 121,106 116,108 112,110 108,113 104,115 100,118 96,120 92,123 88,126 84,129 80,132 77,136 74,140 72,144 69,148 67,152 64,156 " />
    <Polyline x:Name="player4line" Stroke="Cyan" StrokeThickness="4" Points="85,113 89,116 93,119 97,121 102,123 107,124" />
</Canvas>

There must be an easy way to check if those two intersect?

Answer 1

I figured i should search all coordinates around my point, since the stroke thickness is 4.

So I figured I need to check from X-2 to X+2 and from Y-2 to Y+2.

So I did this and amazingly it works for now, I admit it’s not perfect but it’s simple and for now I don’t see any CPU spikes with this method:

  private bool CheckCollision(Point centerPoint)
    {
        bool functionReturnValue = false;

        //wall collision
        if (centerPoint.X - 1 < 0
            || centerPoint.X + 1 > (int)LayoutRoot.ActualWidth
            || centerPoint.Y - 1 < 0
            || centerPoint.Y + 1 > (int)LayoutRoot.ActualHeight)
        {
            functionReturnValue = true;
        }

        //player collision
        if (!functionReturnValue)
        {
            foreach (var player in playerList) //all players are in this list
            {
                for (int i = Convert.ToInt32(centerPoint.X - 2); i < centerPoint.X + 2; i++)
                {
                    for (int j = Convert.ToInt32(centerPoint.Y - 2); j < centerPoint.Y + 2; j++)
                    {
                        var point = new Point() { X = i, Y = j };
                        if (player.CoordinatePoints.Contains(point))
                        {
                            functionReturnValue = true;
                            goto END;
                        }
                    }
                }
            }
        }
        goto END;

     END:
        return functionReturnValue;
    }