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The sims2 windows were a bit weird, in that the two halves (inner and outer wall) of the mesh weren't in the same place, and they were not the same subset. They were put together in-game by the CRES resource moving their position. If you moved one to the wrong place by mistake, or didn't notice it, it would produce exactly the effect you illustrate. Check again that you brought all parts of the sims2 mesh over into your project and have assembled them into a more suitable juxtaposition.
"You can do refraction by raymarching through the depth buffer" (c. Reddeyfish 2017)