从 CGRect 中减去 CGRect——其中最大的一块不包含另一个

我怎样才能减一CGRect来自另一个？我想要结果R1 - R2是 R1 中不与 R2 相交的最大子矩形。

实施例1:

+----------------------------------+
| +--------+                       |
| |   R2   |                       |
| |        |                       |
| +--------+      R1               |
|                                  |
|                                  |
|                                  |
+----------------------------------+
  

R3 = CGRectSubstract(R2,R1);

            +----------------------+
            |                      |
            |                      |
            |                      |
            |          R3          |
            |                      |
            |                      |
            |                      |
            +----------------------+
  

实施例2:

+-----------------------+----------+
|                       |          |
|                       |    R2    |
|                       |          |
|                 R1    +----------+
|                                  |
|                                  |
|                                  |
+----------------------------------+
  

R3 = CGRectSubstract(R2,R1);

+-----------------------+
|                       |
|                       |
|                       |
|          R3           |
|                       |
|                       |
|                       |
+-----------------------+
  

实施例3:

+----------------------------------+
|                                  |
|                                  |
|                                  |
|                 R1               |
|         +---------+              |
|         |         |              |
|         |   R2    |              |
+---------+---------+--------------+
  

R3 = CGRectSubstract(R2,R1);

+----------------------------------+
|                                  |
|                                  |
|              R3                  |
|                                  |
+----------------------------------+



  

你的定义相当模糊，到底是水平减法还是垂直减法呢？我建议结合使用 CGRectIntersection 和 CGRectDivide，并指定一个方向以消除歧义。

（未经测试，甚至编译）

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;
}