I have a scene where I'm using a HDRI image for the background (and have a separate sun inside). The HDRI doesn't contain only sky, but also a bit of the ground. The problem with placing objects in the environment is that they don't cast shadow to the ground (as the ground is part of the hdri).
I am thinking about making a material to put flatly on the ground that would be: a) generally transparent b) giving a grey tint to the places where the objects shadows would be
How would I set a material like this? Or is there maybe a better way to achieve the shadows?
Note: I don't care about it being fully photorealistic with the ground materials etc (as this is obviously impossible), but rather would like to have a rough shadow where it should be.