大佬请帮帮忙，作业七还在理解 shade(p, wo) 函数

[o_o_o_o_o]

问题主要就是 wo, x, ws, NN 如何理解？

– wo: 方向， 可以理解是眼睛 p 指向 👁 的位置？
– N : p 点的 normal？
– x : 光的位置
– ws : x – p ？
– NN : x处的光的 normal
– L\_dir = L\_i * eval(wo, ws, N) * dot(ws, N) * dot(ws, NN) / |x-p|^2 / pdf_light，看课程 slides 难道最后一项的dot(ws, NN)不需要添加一个负号给 ws 么？ 不应该是 dot(-ws,NN)么？

shade(p, wo)
	// p 位置， Vector3f
	// wo 方向，Vector3f ，	
	sampleLight(inter, pdf_light)
	Get x, ws, NN from inter
	// 这样我们sample了光， x, NN 来自光源，
	Shoot a ray from p to x
	// 从 p 点产生一条 ray 照向光
	If the ray is not blocked in the middle
	// 如果这条 ray 中间没有被挡住，那么就说这应该使用直接光照
		L_dir = L_i * eval(wo, ws, N) * dot(ws, N) * dot(ws, NN) / |x-p|^2 / pdf_light
	// 上面这一部分是求直接光照

	L_indir = 0.0
	Test Russian Roulette with probability RussianRoulette wi = sample(wo, N)
	Trace a ray r(p, wi)
	If ray r hit a non-emitting object at q
		L_indir = shade(q, wi) * eval(wo, wi, N) * dot(wi, N) / pdf(wo, wi, N) / RussianRoulette
	Return L_dir + L_indir

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[助教]

实际计算过程中，确实是 dot(-ws,NN)

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[戴皓天]

谢谢助教！昨晚搞了半天，一次渲染都要十几分钟，结果东改改西改改渲染几次图出来都是全黑的😂
原来是这里疏漏了，改了就好了，太粗心了😂

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[condyy]

请问这位大佬orz，是所有的ws都需要取负吗？

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[戴皓天]

不是，这个你画个图就知道了，要判断具体是取正取负你得搞清楚各个物理量的含义

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[戴皓天]

顺便提一句，用castRay的参数ray获取它打到的物体之后记得判断一下Scene::intersect的返回值的happened是否是0，是0的话代表没打到任何物体直接返回Vector3f(0.0f)就行了
不然会报段错误，因为材质是null的话用Material::eval和Material::sample的时候会出错

ps：楼主的理解是对的

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• This reply was modified 4 years ago by 戴皓天.

[o_o_o_o_o]

感谢大佬， ღ( ´･ᴗ･` )比心

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[Songsong]

大佬 想请问一下给的几个intersect函数具体应该使用哪个？想判断测试光线与内部是否有交点感觉不知道该使用哪个。。

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[o_o_o_o_o]

就 scene 里面的 intersect ray

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[condyy]

你好，想问一下wo是不是就是ray的direction取反？？

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[戴皓天]

对的

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[condyy]

再请问一下www，判断相交物体是否发光是不是用的intersection对象的emit参数为000？

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[戴皓天]

我用的办法比较笨，是直接对材质里的一个属性进行判断的，你说的这个我具体不记得了，不过应该也是可以的吧:)

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[Songsong]

想请问一下，采样出的x存在哪个参数里？对结构还是不太熟悉

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[o_o_o_o_o]

我以为是 sampleLight(inter, pdf_light) 然后x存在inter里面

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[Songsong]

好的 感谢哈

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[安安]

请问一下depth变量是用来做什么的呀

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[禹鹏（助教）]

因为是递归算法，所以我们的光线可能弹射很多次，除了俄罗斯轮盘赌的方法来停止光线弹射外，我们也设置了最大的弹射此处，也就是depth。

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[助教]

啊不，我一直没提示是因为希望他们自己意识到这件事，depth 不是用来判停的，而是用来辅助让光源不要全黑的。

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[禹鹏（助教）]

哦哦，确实是这样。是我理解错了。

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[Bear]

我和你理解一样，depth 是另一个递归终止条件。。。

主要是我没用到 Depth 也让光源发光了，用的方法比较朴素

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[o_o_o_o_o]

哈哈哈哈哈~~~感恩各位大佬

至少我的直接光照写出来蛮对的，原来之前在计算中一直犯了一个该死的小错误（这该死的温柔，o(╯□╰)o）

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[DoubleQ]

有个疑问，x是光的位置，那么光的位置为什么可以通过sampleLight函数得到？光的位置难道不是事先就固定好的吗

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