OK, so I may have steered you wrong here…you just need to enable the Transparent Shadow button for all materials the cube will cast upon. Forget the light cross-fade. Now the render-layer/scenes setup is gonna get a lot more complex.
There are 3 separate scenes, Main which contains all objects for render, a shadow only scene (shadows on plane only), and an AO only scene (AO on plane only). You make these latter 2 scenes by duplicating the first scene then making the plane to receive Transparent Shadows and Shadow Only. The AO scene has the lights deleted and the Shadow scene does not use AO.
You’re gonna have to learn how to use the masking tool here:
Scene #1: Cube render layer has All Z enabled so that you can alpha the cube over everything and it still looks like it’s in the proper order instead of riding over the top of the munky in front). If nothing is in front of your transparent object then you can skip the All Z function. Plane in this scene is rendered without shadows or AO. Shadows and AO from other two scenes are recombined to layer over plane.
Scene #2: Transparent Shadows only.
Scene #3: Masking tool is used to subtract cube’s AO from render, slowly ramping it in so that it appears with cube. AO is a trick using the depth buffer so the cube’s AO is always present even though Transparent shadows is enabled. That’s why you gotta mask it out.
Scroll through the 3 open scenes via Ctrl + Right Arrow & Left Arrow (Main, Shadow Only, and AO Only).
If I left out any instructions just ask. I’m getting fairly sick right now and my head is getting kinda fuzzy. If you want your AO color to match the cube you have to do that with the ambient color in the world settings, but if you go and try this then everything is going to get much more complex with the masking and scene setup in order to compensate so that the munky AO isn’t blue also.
You can get somewhat the same effect via a single scene by clicking on the little camera icon next to the AO and Shadow passes on the Plane render layer but you can’t get as fine control over the effect (i.e. just try masking out the AO portion for the cube so that you can ramp it in with the cube’s fade in and watch what happens). This way is gonna teach you how to better navigate the possibilities in Blender and you can get real precision over your effects.
Shadow Manipulation.blend (1.07 MB)