My situation

• Input: a set of rectangles
• each rect is comprised of 4 doubles like this: (x0,y0,x1,y1)
• they are not "rotated" at any angle, all they are "normal" rectangles that go "up/down" and "left/right" with respect to the screen
• they are randomly placed - they may be touching at the edges, overlapping , or not have any contact
• I will have several hundred rectangles
• this is implemented in C#

I need to find

• The area that is formed by their overlap - all the area in the canvas that more than one rectangle "covers" (for example with two rectangles, it would be the intersection)
• I don't need the geometry of the overlap - just the area (example: 4 sq inches)
• Overlaps shouldn't be counted multiple times - so for example imagine 3 rects that have the same size and position - they are right on top of each other - this area should be counted once (not three times)

Example

• The image below contains thre rectangles: A,B,C
• A and B overlap (as indicated by dashes)
• B and C overlap (as indicated by dashes)
• What I am looking for is the area where the dashes are shown

-

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAA--------------BBB
AAAAAAAAAAAAAAAA--------------BBB
AAAAAAAAAAAAAAAA--------------BBB
AAAAAAAAAAAAAAAA--------------BBB
                BBBBBBBBBBBBBBBBB
                BBBBBBBBBBBBBBBBB
                BBBBBBBBBBBBBBBBB
                BBBBBB-----------CCCCCCCC
                BBBBBB-----------CCCCCCCC
                BBBBBB-----------CCCCCCCC
                      CCCCCCCCCCCCCCCCCCC
                      CCCCCCCCCCCCCCCCCCC
                      CCCCCCCCCCCCCCCCCCC
                      CCCCCCCCCCCCCCCCCCC