Collision detection per pixel in drawn user control

Question

I'm creating a small wpf game, where I need some collision detection. I have some fish, which are drawn in expression blend, and I need to know when they collide. But I don't really know how to implement this.

I would like to use per pixel collision detection, and use the bounding rectangle as a cut-off (don't look for collision outside).

But is this at all the smartest way to implement collision detection? I have a path on each figure, is this information useful. As I see it, I don't achieve much from it, because it's not straight lines, but curved.

Any help will really be appreciated :)

Answer 1

This has not been tested, but try something like:

public bool CollidsWith(FrameworkElement sprite1, FrameworkElement sprite2, bool pixelPerfect)
{
    try
    {
        Rect r1 = Bounds(sprite1);
        Rect r2 = Bounds(sprite2);

        if (r1.IntersectsWith(r2))
        {
            if (!pixelPerfect)
                return true;
            else
            {
                Point pt = new Poin();                            
                for (int x = (int)r1.Left; x < (int)r1.Right; x++)
                {
                    for (int y = (int)r1.Top; y <(int)r1.Bottom; y++)
                    {
                        pt.X = x;
                        pt.Y = y;
                        if (VisualTreeHelper.HitTest(sprite2, pt) != null)
                            return true;
                    }
                }
                return false;
            }
            else
                return false;
        }
    }
    catch { }
    return false; // we should not get here
}

public Rect Bounds(FrameworkElement sprite)
{
    get
    {
        Point ptBottomRight = new Point(sprite.Position.X + sprite.RenderSize.Width, sprite.Position.Y + RenderSize.Height);
        return new Rect(sprite.Position, ptBottomRight);
    }
}