Light Cookie Doubles up Lighting on Transparent Objects ?

Questions & Answers
1

I came across this strange thing today, apparently when when light cookies are set, transparent objects that overlap themselves (so not regular transparent objects) behave weirdly as seen in the image.

I have tried a lot of things but it seems the only thing that fixes it is disabling pixel lighting (aka both forward and deferred) in either a new shader or per light, unfortunately I need this as I want to have a normal map on my transparent objects.

924-cookieexample.jpg

Any ideas would be greatly appreciated, Here is also a link to a stripped down project that shows the basic issue. :

https://dl.dropbox.com/s/6awohhm3jrh31vz/LightCookieExample.unitypackage?dl=1

2

this causes by lighting calculations in shader.

light calculated as diffuse_color * light_power * alpha

so for top-left picture light power is calculated normally, but it top-right picture your alpha-component is doubled (50% opaque and 50% opaque in a single pixel gives totally 75% opaque), so light have increased power in that area

solution is not to use overlapping geometry in single model. better to use shader with texture overlapping - cheapy method without such bugs with light

other solution is to write a custom shader for correct blend of such surfaces