Shadows for Augmented Reality

[stevenlovegrove]

Hi all - I'm pretty new to Bevy and was looking for some advice on achieving an effect I'm after for an Augmented Reality scene over a video overlay. Given a video stream with a little character I'm animating sat on a desk over the top, how do I render their shadow?

Is there a simple way to convince Bevy to render the shadow as black over a transparent buffer? I understand that shading is normally achieved with a shadow map and a depth test during the lighting pass. Is there some way to mess with the parameters of that pipeline to have it behave similarly against a hidden plane but where we add black instead of defining the shadow to be the absence of contribution from the light? If I have to resort to writing a custom shader / pipeline, what is the simplest way to do approach that (example links appreciated!)?

Thanks!