Material instances in realistic rendering example

Checking out the realistic rendering example, I’ve seen the same material instance is applied to all the books. If I change the color of the instance, it changes for all the books. From the documentation and from other questions on answerhub I seem to understand that you need different instances in order to have different parameters.
How can I change instance parameters for a single mesh? (e.g. the color of the different books in the scene?)
(sorry, I’m probably missing out on some basics about how material instances work!)

You need to create an MIC for any frequency that you want to set the property. So if you want to be able to tweak all of the book’s color, but also add a per-mesh tint, you should make one parent MIC where you set the book’s color, then an MIC for each mesh where you set the per-mesh tint, which has the book MIC as its parent.

Thank you Daniel, but it the realistic rendering demo is this really done this way? In the Game/Archviz/Material folder I found M_Book_Mat and M_Book_Mat_Inst, but cannot find all the MICs for the different tints of the books, and all the books seem to be referencing M_Book_Mat_Inst.
Am I looking in the wrong place?

Open up the material, not the instance and you’ll see how it works. Every book has a different color even though they have the same material because it uses the object position to pick a color. If you want to manually set color for every individual book then you need a simpler material, but separate material instances for every book.

Ok, I’m starting to understand. What still puzzles me is that if pick a book and drag it around, the color does not change. Wouldn’t it be supposed to change?

Hey devel.bmad -

So if you look at the master material the Object position is broken up with a Frac. A Frac node will return only the decimal of the value inputted, so for instance if you have a value of 100.456 then Frac it you will only get .456. Since most everyone has the snaps on you will not move by any fractional amount but instead in values as low as 1 but the fraction amount remains the same. If you turn snap off or move by typing in an amount, the book will change color.

Thank You

Eric Ketchum

That’s it! Thank you Eric