Code of FC-Algorithm for Line Clipping in C++ Programming language

fc-algorithm.cpp

void Clip1Left(point &A, point &B, point Pmin, point Pmax) 
{
	A.y = B.y - (B.x - Pmin.x) * (B.y - A.y) / (B.x - A.x);
	A.x = Pmin.x;
}

void Clip1Top(point &A, point &B, point Pmin, point Pmax)
{
	A.x = B.x - (B.y - Pmax.y) * (B.x - A.x) / (B.y - A.y);
	A.y = Pmax.y;
}

void Clip1Bottom(point &A, point &B, point Pmin, point Pmax)
{
	A.x = B.x - (B.y - Pmin.y) * (B.x - A.x) / (B.y - A.y);
	A.y = Pmin.y;
}

void Clip2Right(point A, point &B, point Pmin, point Pmax)
{
	B.y = A.y + (Pmax.x - A.x) * (B.y - A.y) / (B.x - A.x);
	B.x = Pmax.x;
}

void Clip2Top(point A, point &B, point Pmin, point Pmax)
{
	B.x = A.x + (Pmax.y - A.y) * (B.x - A.x) / (B.y - A.y);
	B.y = Pmax.y;
}

void Clip2Bottom(point A, point &B, point Pmin, point Pmax)
{
	B.x = A.x + (Pmin.y - A.y) * (B.x - A.x) / (B.y - A.y);
	B.y = Pmin.y;
}

// FC-Algorithm
bool clip(point &A, point &B, point Pmin, point Pmax)
{
	// 1
	if (A.x > B.x) std::swap(A, B);

	// 2
	int C1 = 0;
	if (A.x < Pmin.x) C1 += 1;
	if (A.x > Pmax.x) C1 += 2;
	if (A.y < Pmin.y) C1 += 4;
	if (A.y > Pmax.y) C1 += 8;
			
	int C2 = 0;
	if (B.x < Pmin.x) C2 += 1;
	if (B.x > Pmax.x) C2 += 2;
	if (B.y < Pmin.y) C2 += 4;
	if (B.y > Pmax.y) C2 += 8;

	// 3
	if (C1 & C2) return false;

	// 4
	int C = C1 * 16 + C2;

	switch (C) {
		// 5
		case 0x00: return true;

		// 6
		case 0x02: {
			Clip2Right(A, B, Pmin, Pmax);
			return true;
		}

		// 7
		case 0x04: {
			Clip2Bottom(A, B, Pmin, Pmax);
			return true;
		}

		// 8
		case 0x06: {
			Clip2Right(A, B, Pmin, Pmax);

			if (B.y < Pmin.y) Clip2Bottom(A, B, Pmin, Pmax);
			return true;
		}

		// 9
		case 0x08: {
			Clip2Top(A, B, Pmin, Pmax);
			return true;
		}

		// 10
		case 0x0A: {
			Clip2Right(A, B, Pmin, Pmax);

			if (B.y > Pmax.y) Clip2Top(A, B, Pmin, Pmax);
			return true;
		}

		// 11
		case 0x10: {
			Clip1Left(A, B, Pmin, Pmax);
			return true;
		}

		// 12
		case 0x12: {
			Clip1Left(A, B, Pmin, Pmax);
			Clip2Right(A, B, Pmin, Pmax);
			return true;
		}

		// 13
		case 0x14: {
			Clip1Left(A, B, Pmin, Pmax);

			if (A.y < Pmin.y) return false;
			else Clip2Bottom(A, B, Pmin, Pmax);
			return true;
		}

		// 14
		case 0x16: {
			Clip1Left(A, B, Pmin, Pmax);

			if (A.y < Pmin.y) return false;
			else Clip2Bottom(A, B, Pmin, Pmax);
			
			if (B.x > Pmax.x) Clip2Right(A, B, Pmin, Pmax);
			return true;
		}

		// 15
		case 0x18: {
			Clip1Left(A, B, Pmin, Pmax);

			if (A.y > Pmax.y) return false;
			else Clip2Top(A, B, Pmin, Pmax);
			return true;
		}

		// 16
		case 0x1A: {
			Clip1Left(A, B, Pmin, Pmax);

			if (A.y > Pmax.y) return false;
			else Clip2Top(A, B, Pmin, Pmax);

			if (B.x > Pmax.x) Clip2Right(A, B, Pmin, Pmax);
			return true;
		}

		// 17
		case 0x40: {
			Clip1Bottom(A, B, Pmin, Pmax);
			return true;
		}

		// 18
		case 0x42: {
			Clip1Bottom(A, B, Pmin, Pmax);

			if (A.x > Pmax.x) return false;
			else Clip2Right(A, B, Pmin, Pmax);
			return true;
		}

		// 19
		case 0x48: {
			Clip1Bottom(A, B, Pmin, Pmax);
			Clip2Top(A, B, Pmin, Pmax);
			return true;
		}

		// 20
		case 0x4A: {
			Clip1Bottom(A, B, Pmin, Pmax);

			if (A.x > Pmax.x) return false;
			else Clip2Right(A, B, Pmin, Pmax);

			if (B.y > Pmax.y) Clip2Top(A, B, Pmin, Pmax);

			return true;
		}

		// 21
		case 0x50: {
			Clip1Left(A, B, Pmin, Pmax);

			if (A.y < Pmin.y) Clip1Bottom(A, B, Pmin, Pmax);

			return true;
		}

		// 22
		case 0x52: {
			Clip1Bottom(A, B, Pmin, Pmax);

			if (A.x > Pmax.x) return false;
			else if (A.x < Pmin.x) Clip1Left(A, B, Pmin, Pmax);
			
			Clip2Right(A, B, Pmin, Pmax);
			return true;
		}

		// 23
		case 0x58: {
			Clip1Left(A, B, Pmin, Pmax);

			if (A.y > Pmax.y) return false;
			else if (A.y < Pmin.y) Clip1Bottom(A, B, Pmin, Pmax);

			Clip2Top(A, B, Pmin, Pmax);
			return true;
		}

		// 24
		case 0x5A: {
			Clip1Left(A, B, Pmin, Pmax);

			if (A.y > Pmax.y) return false;
			else if (A.y < Pmin.y) {
				Clip1Bottom(A, B, Pmin, Pmax);
				if (A.x > Pmax.x) return false;
			}

			Clip2Top(A, B, Pmin, Pmax);

			if (B.x > Pmax.x) Clip2Right(A, B, Pmin, Pmax);
			return true;
		}

		// 25
		case 0x80: {
			Clip1Top(A, B, Pmin, Pmax);
			return true;
		}

		// 26
		case 0x82: {
			Clip1Top(A, B, Pmin, Pmax);

			if (A.x > Pmax.x) return false;
			else Clip2Right(A, B, Pmin, Pmax);
			return true;
		}

		// 27
		case 0x84: {
			Clip1Top(A, B, Pmin, Pmax);
			Clip2Bottom(A, B, Pmin, Pmax);
			return true;
		}

		// 28
		case 0x86: {
			Clip1Top(A, B, Pmin, Pmax);

			if (A.x > Pmax.x) return false;
			else Clip2Right(A, B, Pmin, Pmax);

			if (B.y < Pmin.y) Clip2Bottom(A, B, Pmin, Pmax);
			return true;
		}

		// 29
		case 0x90: {
			Clip1Left(A, B, Pmin, Pmax);

			if (A.y > Pmax.y) Clip1Top(A, B, Pmin, Pmax);
			return true;
		}

		// 30
		case 0x92: {
			Clip1Top(A, B, Pmin, Pmax);

			if (A.x > Pmax.x) return false;
			else if (A.x < Pmin.x) Clip1Left(A, B, Pmin, Pmax);

			Clip2Right(A, B, Pmin, Pmax);
			return true;
		}

		// 31
		case 0x94: {
			Clip1Left(A, B, Pmin, Pmax);

			if (A.y < Pmin.y) return false;
			else if (A.y > Pmax.y) Clip1Top(A, B, Pmin, Pmax);

			Clip2Bottom(A, B, Pmin, Pmax);
			return true;
		}

		// 32
		case 0x96: {
			Clip1Left(A, B, Pmin, Pmax);

			if (A.y < Pmin.y) return false;
			else if (A.y > Pmax.y) {
				Clip1Top(A, B, Pmin, Pmax);
				if (A.x > Pmax.x) return false;
			}

			Clip2Bottom(A, B, Pmin, Pmax);

			if (B.x > Pmax.x) Clip2Right(A, B, Pmin, Pmax);
			return true;
		}
	}
}