InfiniteAreaLight中使用AliasMethod的疑惑

[hegaoxiang]

u聚，在这里InfiniteAreaLight初始化这里，sum不是要再除以(w*h)才等于贴图这个二维函数在定义域上的积分吗？如果这里不除的话，distribution中的值应该并不是pdf(i,j)吧，应该只是个分布，若是这样的话。好像u聚在AliasMethod却是直接把他当作pdf了。

	auto w = img->GetWidth();
	auto h = img->GetHeight();
	vector<double> distribution(w*h);
	double sum = 0.f;
	for (int y = 0; y < h; y++) {
		double sinTheta = sin(PI<float> * (y + 0.5) / static_cast<double>(h));
		for (int x = 0; x < w; x++) {
			int idx = img->xy2idx(x, y);
			distribution[idx] = sinTheta * img->GetPixel(x, y).to_rgb().illumination();
			sum += distribution[idx];
		}
	}

	for (auto & p : distribution)
		p /= sum;

	aliasMethod.Init(distribution);


......
void AliasMethod::Init(const vector<double> & distribution) {
	......
	for (int i = 0; i < num; i++) {
		// 默认设置为 i
		table[i].k = static_cast<int>(i);

		table[i].p = distribution[i];
		table[i].u = num * distribution[i];

		if (table[i].u < 1)
			underfulls.push_back(i);
		if (table[i].u > 1)
			overfulls.push_back(i);
	}

	......
}