/// <summary> Returns the parts of a not overlapping with b. </summary>
public static Rect[] Subtract(Rect a, ref Rect b)
{
var legs = a.GetCorners().Count(b.Contains);
if (legs == 0)
{
return a.Substract0Legged(ref b);
}
else if (legs == 1)
{
return a.Substract1Legged(b);
}
else if (legs == 2)
{
return a.Substract2Legged(b);
}
else
{
Contract.Assert(legs == 4);
return EmptyCollection<Rect>.Array; //rect is already contained in r
}
}
/// <summary> Returns parts of a that are not contained in b, assuming that no corner of a is in b. </summary>
public static Rect[] Substract0Legged(this Rect a, ref Rect b)
{
bool rightQ = b.Left <= a.Right && a.Right < b.Right; //a.right is in b
bool leftQ = b.Left <= a.Left && a.Left < b.Right; //a.left is in b
bool topQ = b.Top <= a.Top && a.Top < b.Bottom; //a.top is in b
bool bottomQ = b.Top <= a.Bottom && a.Bottom < b.Bottom; //a.bottom is in b
//no corner of a may be in b
Contract.Assert(!(leftQ && topQ));
Contract.Assert(!(rightQ && topQ));
Contract.Assert(!(rightQ && bottomQ));
Contract.Assert(!(leftQ && bottomQ));
int invCornerCount = b.GetCorners().Count(a.Contains);
if (invCornerCount == 2)
{
Rect[] result = Substract2Legged(b, a);
b = a; //must be set after calling Substract2Legged
return result;
}
else if (invCornerCount == 4)
{
b = default(Rect);
return new[] { a };
}
if (leftQ && rightQ)
{
//b is horizontal
if (b.Bottom <= a.Top || b.Top >= a.Bottom)
{
//no intersection
}
else
{
//top part of a:
Rect result1 = FromExplicitCoordinates(a.Left, a.Right, a.Top, b.Top);
//bottom part of a:
Rect result2 = FromExplicitCoordinates(a.Left, a.Right, b.Bottom, a.Bottom);
return new[] { result1, result2 };
}
}
else if (topQ && bottomQ)
{
//b is vertical
if (b.Left >= a.Right || b.Right <= a.Left)
{
//no intersection
}
else
{
//left part of a:
Rect result1 = FromExplicitCoordinates(a.Left, b.Left, a.Top, a.Bottom);
//right part of b:
Rect result2 = FromExplicitCoordinates(b.Right, a.Right, a.Top, a.Bottom);
return new[] { result1, result2 };
}
}
//no intersection
return new[] { a };
}
