| 50 | //------------------------------------------------------------------------------ |
| 51 | |
| 52 | bool IsClockwise(const Polygon &poly) |
| 53 | { |
| 54 | int highI = poly.size() -1; |
| 55 | if (highI < 2) return false; |
| 56 | double a; |
| 57 | a = static_cast<double>(poly[highI].X) * static_cast<double>(poly[0].Y) - |
| 58 | static_cast<double>(poly[0].X) * static_cast<double>(poly[highI].Y); |
| 59 | for (int i = 0; i < highI; ++i) |
| 60 | a += static_cast<double>(poly[i].X) * static_cast<double>(poly[i+1].Y) - |
| 61 | static_cast<double>(poly[i+1].X) * static_cast<double>(poly[i].Y); |
| 62 | //area := area/2; |
| 63 | return a > 0; //ie reverse of normal formula because assume Y axis inverted |
| 64 | } |
| 65 | //------------------------------------------------------------------------------ |
| 66 | |
| 67 | bool IsClockwise(PolyPt *pt) |