I plan to fake a shadow from a light using a mask (in the area light's material I mixed a black 0 strength emission shader with another one that actually casts light). However, the result is nothing. My mask texture is black and white. The shadow is a window frame as it seems. Is it possible to do this? if so, how?
I think textured area lights are not fully supported yet. So currently one of the workarounds is to add another mesh under the lamp and add a transparent material on it with transparency controlled by the mask image (as seen below).
Another way is to add Texture Coordinates node to your existing area lamp material and connect the Reflection output to the Image Texture Vector input, however, that looks kinda strange and not very correct.