Object Type at Coordinate on Canvas

Question

How can I determine what type of element is at a given coordinate on a canvas?

I am making tetris and have polygons dropping down the canvas. I wish to check position (50,50) for example, and see if that point contains a polygon or not.

Basically I want to do collision detection, and can't find an easy way to do it since my polygons are not all rectangular.

Sam Hobbs · Answer

Also try: http://social.msdn.microsoft.com/Search/en-US?query=hit%20test%20wpf&resultsLang=en-US&beta=0&ac=1 I am not sure that will help, but I think it is worth looking at.

Jaganathan Bantheswaran · Answer

Do you need the solution for your query or Need to know where i got the posted code.

David Kay · Answer

Why is there BotBody, BattleArena in the code? Where did you get this code from?

Jaganathan Bantheswaran · Answer

Instead of Rectangle, we can use polygon right?. Just try it.

David Kay · Answer

but that's for rectangles only right? it would be more complex for non rectangular polygons wouldn't it?

Jaganathan Bantheswaran · Answer

Hi, There is a Method called IntersectsWith in System.Drawing which will say you that whether a rect 1 intersects the rect 2. See the example. public Rect GetBounds(FrameworkElement of, FrameworkElement from) { // Might throw an exception if of and from are not in the same visual tree GeneralTransform transform = of.TransformToVisual(from); return transform.TransformBounds(new Rect(0, 0, of.ActualWidth, of.ActualHeight)); } Vehicle IsBotCollided(IEnumerable blist) { //currentBounds is of type Rect, which contains the 4 points of the rectangle (even when rotated) var currentBounds = GetBounds(BotBody, BattleArena); //Then I check if the current bounds intersect with each of the other Bots` bounds that are also in the Arena foreach (Vehicle vehicle in blist) { if(GetBounds(vehicle.BotBody, BattleArena).IntersectsWith(currentBounds)) { return vehicle; } } return null; }

Vulpes · Answer

There's some code in this thread ( http://social.msdn.microsoft.com/Forums/en-US/winforms/thread/95055cdc-60f8-4c22-8270-ab5f9870270a/ ) which can determine whether or not a given point is contained within a polygon. As you'll see the vertices of the polygon need to be passed as an array of Points.