I have a collision detection class that works by finding the distance between the centres and whether that distance is small enough to be a collision (see Collision Detection error). My problem is trying to make this actually work, with ellipses colliding. I will explain more if necessary. Thx
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who do specifiy the location (rotation etc.) of an ellipse? or do you mean circles?raisyn– raisyn2010-08-22 08:00:49 +00:00Commented Aug 22, 2010 at 8:00
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2 Answers
The best way would to implement per pixel collision detection when the images are overlapping you can read more about this in the following links
http://www.codeproject.com/KB/game/collision3.aspx
Per-pixel collision problem in C#
I also did a problem like this for a project a few years ago when I needed to detect if two circles overlapped where i used the following code
public static bool Intersect(Rectangle rectangle1, Rectangle rectangle2)
{
if (((rectangle1.X < (rectangle2.X + rectangle2.Width)) && (rectangle2.X < (rectangle1.X + rectangle1.Width))) && (rectangle1.Y < (rectangle2.Y + rectangle2.Height)) && (rectangle2.Y < (rectangle1.Y + rectangle1.Height)))
{
Vector2 rect1Centre = new Vector2(rectangle1.X + rectangle1.Width / 2, rectangle1.Y + rectangle1.Height / 2);
Vector2 rect2Centre = new Vector2(rectangle2.X + rectangle2.Width / 2, rectangle2.Y + rectangle1.Height / 2);
double radius1 = ((rectangle1.Width / 2) + (rectangle1.Height / 2)) / 2;
double radius2 = ((rectangle2.Width / 2) + (rectangle2.Height / 2)) / 2;
double widthTri = rect1Centre.X - rect2Centre.X;
double heightTri = rect1Centre.Y - rect2Centre.Y;
double distance = Math.Sqrt(Math.Pow(widthTri, 2) + Math.Pow(heightTri, 2));
if (distance <= (radius1 + radius2))
return true;
}
return false;
}
Not very nice code but I wrote it doing my first XNA game
3 Comments
Jason Quinn
rectangle1.X is the X coordinate of the centre of the rectangle and rectangle1.Y is the Y coordinate
Apophis
Cheers man but how can I make it apply to existing objects, rather than ones created by the method?
Jason Quinn
@NeoHaxxor I really depends on how many object you have, I only had 3 circles (it was an Air Hockey game) so I had an event handler on each one and every time one of them moved I checked it against the other rectangles. If you have a lot of objects that need to be checked there are probably some far better ways.
I had the same problem recently. Circle overlap is easy to determine. With ellipses it's trickier, but not that bad. You play around with the ellipse equation for a while, and the result comes up:
//Returns true if the pixel is inside the ellipse
public bool CollisionCheckPixelInEllipse(Coords pixel, Coords center, UInt16 radiusX, UInt16 radiusY)
{
Int32 asquare = radiusX * radiusX;
Int32 bsquare = radiusY * radiusY;
return ((pixel.X-center.X)*(pixel.X-center.X)*bsquare + (pixel.Y-center.Y)*(pixel.Y-center.Y)*asquare) < (asquare*bsquare);
}
// returns true if the two ellipses overlap
private bool CollisionCheckEllipses(Coords center1, UInt16 radius1X, UInt16 radius1Y, Coords center2, UInt16 radius2X, UInt16 radius2Y)
{
UInt16 radiusSumX = (UInt16) (radius1X + radius2X);
UInt16 radiusSumY = (UInt16) (radius1Y + radius2Y);
return CollisionCheckPixelInEllipse(center1, center2, radiusSumX, radiusSumY);
}
1 Comment
Apophis
Cheers man. Just one more thing though - being able to make the method trigger a translatetransform method? The details of the code aren't a problem, I've coded it, just having the above code return true and triggering this code. Thx