>> 1. Set render target to temporary one
>> 2. Render scene without ghost normally, but set stencil writes to always 
>> 0
>> 3. Render ghost geometry without writes to RGBA, but stencil write of 
>> always 1
>> 4. Switch the render target to the actual back buffer
>> 5. Render a full-screen quad to simply copy over the entire temp buffer 
>> RGBA contents
>> 5. Set your special effect pixel shader
>> 6. Set stencil pass function to equal 1
>> 7. Render a full-screen quad at the depth of the ghost (this will avoid 
>> affecting anything infront of the ghost)
>> 8. Render the ghost normally
>
> I was following you up until 7. First, since the ghost is a model, I'm not 
> sure what the single "depth" would be.

If you wanted everything behind the ghost in the scene to be affected, then 
I would set the "depth" to the furthest away point of the model (but maybe 
experiemtn, I don't know how much of an effect it would have with 
intersecting geometry).

> But OK, assuming I'm not actually intersecting geometries with the ghost, 
> I can work with that.  However, doesn't step 5 destroy the original depth 
> information?

No, you should be able to control the RGBA render target and the 
depth/stencil target separately.  In DirectX you call 
SetDepthStencilSurface.  For my algorithm I assumed a single Depth/Stencil 
surface would be persistent throughout the whole process,

> Secondly, I'm not sure what 7 is for at all.

It applies the shader as you requested here: "Basically, I want to apply a 
screen-space shader but only to parts of the
scene occluded by a model which is in turn partially occluded by other parts
of the scene."

> Does step 8 mean "render the parts of the ghost you can't see through" or 
> something?

I assume your actual ghost model has varying levels of transparency, 
otherwise there would be no point in applying some shader to the scene 
behind it.  Step 8 means render the ghost as normal - of course the 
background will already be distorted somehow due to Step 7.

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