Different Materials for Alpha, Transparency, Emission

Jumbee

I saw people separating uv islands that have alpha or transparency on them into a different texture set. And a new material is created for it.

For example: if there is a broken window object:

Opaque parts are being put into one texture and a material created for it.

Even if there is a still room for transparent glass parts: they are being put into different texture set and a new material is created for it.

What is the reasoning behind this method?

Is this method specific to a certain game engine? (they were using unity)

What is the keyword for the term i am looking for?

Thank you for your answers.

Fabi_G

The asset was likely done this way because see-through elements (glass) used a different shader with higher cost than the opaque parts of the asset. This way, in a higher LOD of the asset the expensive glass material instance could be swapped out with a cheaper one.

You can probably learn some more about it the documentation of the game engine you are using, eg. Material Blend Modes in UE

Jumbee

Let me ask it his way:

Since we have to use different renderin mode in Unity for transparent objects. >Does changing a materials 'rendering mode' effect the performance?, from opaque to lets say cutout, fade or transparent.

Lets say: If we have a texture with no alpha value but still enable the cutout rendering mode would it cost any performance?

If yes, then it makes sense to separate the textures with alphas into different materials.

rexo12

yes and yes. I believe cut-out will have some flat overhead for sampling your alpha channel regardless of whether any pixels are actually 'cut'.

Fabi_G has given a pretty definite answer.