Why doesn't this lightmap capture the correct shadow? I'm trying to bake lightmaps. This is how my scene looks like as rendered by cycle:



As you can see, the blinds should cast shadow on the floor. I then wanted to generate lightmaps that can capture this shadow for real time rendering. But I don't know why, the lightmap doesn't contain this shadow, but a few gray patches. 



The uv mapping seems to be correct.
I got it now. The problem was that the floor and walls had their normal flipped. After I checked backface culling, this became obvious. Fixing the normal direction solved the problem.