Controlled blending for sprites

Hi!

I just know the very basics of shader syntax, so I apologize if this is a basic question. I have a 2D scene and an orthographic camera... I figured the "Particle Multiply Double" shader would work nicely as a fake sprite based lighting, and it kind of does. Sort of like a flash light. My problem is that I have a background that's far in the distance (a sky), that should not be "illuminated". So, i have:

A: A background (way back)
B: A foreground (that I want to "illuminate" using my sprite)
C: A round light shape sprite (currently with the multiply double shader)

This picture show the setup I have, and what I want. (I faked the blending in photoshop, so it's perhaps not exactly what Unity would look like, but it gets the point across).



A and B are sprites also, and preferably I'd like them to remain sprites...

I know layers are a Unity runtime feature and not accesible in shaders, but is there any way I can achieve this effect? Like some depth hack in the shader? Sprite sorting wouldn't work (right?) since I can't have A<B<C in geometry but B<C<A in blending... Was thinking about multiple cameras and rendering the background last, but how to "cut out" the other stuff in that case...

Any tips greatly appreciated!

 

Hello,

I see two options for this, One would be messing with Depth (A > C > B) and rendering C later (Queue changed) with Ztest Greater instead of the default LEqual. But I never tested it with sprites so I can't be sure Depht is resolved as usual 3D stuff.

The other solution would be to use the Stencil buffer (http://docs.unity3d.com/Manual/SL-Stencil.html). A and B would be rendered before C (C with a Queue changed). B could use a Stencil like

Code (CSharp):

1. Stencil
2.             {
3.                 Ref 2
4.                 Comp always
5.                 Pass replace
6.             }

and C with

Code (CSharp):

1. Stencil
2.             {
3.                 Ref 2
4.                 Comp equal
5.             }

PS : I had a bug with Unity 5.2 when changing render Queue wouldn't be effective unless you reset the shader in the material (like drag&drop the shader on the material again to make sure it's reset).

 

It works using the stencil buffer, thanks a lot @Fuegan!

I did have an issue if B is partially transparent, where it would write to the stencil buffer also some of the completely transparent pixels. I solved that by using an AlphaTest Greater .01 on the shader for B.