Subtract CGRect from CGRect -- largest piece of one not containing the other
How I can substract one CGRect from another? I want the result R1 - R2 to be the largest subrectangle of R1 that does not intersect R2.
Example 1:
+----------------------------------+ | +--------+ | | | R2 | | | | | | | +--------+ R1 | | | | | | | +----------------------------------+
R3 = CGRectSubstract(R2,R1);
+----------------------+
| |
| |
| |
| R3 |
| |
| |
| |
+----------------------+
Example 2:
+-----------------------+----------+ | | | | | R2 | | | | | R1 +----------+ | | | | | | +----------------------------------+
R3 = CGRectSubstract(R2,R1);
+-----------------------+ | | | | | | | R3 | | | | | | | +-----------------------+
Example 3:
+----------------------------------+ | | | | | | | R1 | | +---------+ | | | | | | | R2 | | +---------+---------+--------------+
R3 = CGRectSubstract(R2,R1);
+----------------------------------+ | | | | | R3 | | | +----------------------------------+
Answer
Your definition is fairly ambiguous, what says whether the subtraction is horizontal or vertical? I recommend using a combination of CGRectIntersection and CGRectDivide, along with specifying a direction to remove ambiguity.
(not tested, or even compiled)
CGRect rectSubtract(CGRect r1, CGRect r2, CGRectEdge edge) {
// Find how much r1 overlaps r2
CGRect intersection = CGRectIntersection(r1, r2);
// If they don't intersect, just return r1. No subtraction to be done
if (CGRectIsNull(intersection)) {
return r1;
}
// Figure out how much we chop off r1
float chopAmount = (edge == CGRectMinXEdge || edge == CGRectMaxXEdge)
? intersection.size.width
: intersection.size.height;
CGRect r3, throwaway;
// Chop
CGRectDivide(r1, &throwaway, &r3, chopAmount, edge);
return r3;
}