CODEWITHSUNDEEP
gdi
Chandan Kumar Rath
Chandan Kumar Rath

Reputation: 157

How to detect if my mouse position is within a rectangle c#?

I am trying to write an application to draw schematic diagrams which contain rectangles, lines and circles. Now I want to add another functionality to drag a rectangle to different position. The problem I am facing is to detect whether I have clicked within a rectangle or not. I know there is a function like Rectangle.Contains(Point). To use such method I need to use a for loop to check against each rectangle. If I have a large number of rectangles present, then its not wise to use this method. Is there any other way to do this task.

Upvotes: 1

Views: 5202

Answers (4)

Anben PANGLOSE
Anben PANGLOSE

Reputation: 116

You need to use a spatial index to find quickly in which rectangle the mouse is. I suggest a R-tree, here is the theorical part:

http://en.wikipedia.org/wiki/R-tree

And the c#,implementation:

http://sourceforge.net/projects/cspatialindexrt/

Create an rtee, add your rectangles then call the rtree.nearest method with the mouse coordinate to know the rectangles containing the mouse cursor. You can play with the distance parameter.

Hope it helps,

Anben Panglose.

Upvotes: 1

Faruk
Faruk

Reputation: 5821

May be something like this?

 public bool isRectangelContainPoint(RectangleF rec, PointF pt)
    {
        if (pt.X >= rec.Left && pt.X <= rec.Right && pt.Y <= rec.Bottom && pt.Y >= rec.Top)
            return true;
        else
            return false;
    }

Upvotes: 0

perpenso
perpenso

Reputation: 379

You need a computer graphics textbook, this and similar problems are often discussed.

If memory serves me, make sure the point is below the top edge of the rectangle, above the bottom edge, left of the right edge and right of the left edge.

Regarding testing a bunch of rectangles in a loop. Consider having a circle that each rectangle fits in, a bounding circle. First test to see if the point is farther from the origin of the circle than the radius of the circle. If so there is no need to test the rectangle, its a miss. OK, that was a very theoretical answer. In reality calculating the distance from the point to the origin can be a very expensive calculation, it involves a square root, it may be faster to do the four comparisons of the point in rectangle check. Again if memory servers me, we don't really care what the distance from the origin is only if it is greater than the radius. So only partially perform the distance calculation, omitting the final square root, and compare against the square of the radius. Of course you still need to experiment and profile to make sure this bounding circle check is faster than just doing the regular point in rectangle check and you need to make sure you will have sufficient misses to offset the hits where you will end up doing both the bounding circle and rectangle checks.

Upvotes: 3

Vinayak Kolagi
Vinayak Kolagi

Reputation: 1881

I would go about dividing the display region into a quadrant. Then place the rectangles into top-left, top-right, bottom-left, bottom-right grids. Placing them means, creating a list for every quadrant and placing the rectangles in it.

Once the point is clicked, determine which quarter it belongs to and search in those rectangles only. This approach reduces your linear search by 4 times.

Remember that you need to also take care of overlapping where the point can belong to many rectangles. Here the z-order of your rectangles matter. So while the list is maintained for a quadrant, it should be sorted with it's z-order as a key.

Hope this helps.

Upvotes: 0

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