struct BezierSurface {
	std::vector<BezierCurve> bcs;
public:
	void AddCurve(BezierCurve bc) {
		bcs.push_back(bc);
	}
	float B(int i, float t) {
		int n = bcs.size()-1;
		float choose = 1;
		for (int j = 1; j <= i; j++)
			choose *= (float)(n - j + 1) / j;
		return choose * pow(t, i) * pow(1 - t, n - i);
	}
	float Bd(int i, float t) {
		return (bcs.size() - 1)*(B(i - 1, bcs.size() - 1) - B(i, bcs.size() - 1));
	}
	vec4 r(float t, float u) {
		vec4 rr(0, 0, 0);
		for (unsigned int i = 0; i < bcs.size(); i++){
			for (unsigned int j = 0; j < bcs[i].cps.size(); j++){
				rr = rr + bcs[i].cps[j] * B(i, u)*B(j, t);
			}
		}
		return rr;
	}
	vec4 Dt(float t, float u) {
		vec4 rr(0, 0, 0);
		for (unsigned int i = 0; i < bcs.size(); i++) {
			for (unsigned int j = 0; j < bcs[i].cps.size(); j++) {
				rr = rr + bcs[i].cps[j] * B(i, u) * Bd(j, t);
			}
		}
		printf("%f, %f, %f\n", rr.v[0], rr.v[1], rr.v[2]);
		return rr;
	}
		vec4 Du(float t, float u) {
			vec4 rr(0, 0, 0);
			for (unsigned int i = 0; i < bcs.size(); i++) {
				for (unsigned int j = 0; j < bcs[i].cps.size(); j++) {
					rr = rr + bcs[i].cps[j] * Bd(i, u) * B(j, t);
				}
			}
			printf("%f, %f, %f\n", rr.v[0], rr.v[1], rr.v[2]);
			return rr;
		}
};