Also, I found that 2 materials CAN have the same name in a specific case: If you name one material Color_000 for example, it will be named like the Sketchup internal material of the same name: [Color_000]. (It seems that the SDK removes the brakets '[' and ']' when you get the name of an internal material with SUMaterialGetName()).

Ok thank you! I though 2 materials could have the same name.

I don't really understand how it is possible to have no persistent ID. In the skp file: how each face knows to which material it is bound? I supposed there is an ID saved with the face that tells which material is linked to the face.

Then how can I find: starting from a ruby API material: the corresponding SDK material ?

I discovered that the entityID (for materials) is not the same when getting it from the Ruby API or the cpp SDK:

Example (using the same material in both example)

Ruby API

//aMat is a material
aMat.entityID
//Returns 183 

Cpp SDK

//aMat is a SUMaterialRef
int id;
SUEntityRef entity = SUMaterialToEntity(aMat );
SUEntityGetID(entity , &id);
uint matID = (uint) id;
//Returns 201

I tested this using a custom attribute dict to make sure it is the same material in both cases, it seems that the material in the SDK has always an ID of +18, and if I don't cast it to a uint, its value is always negative.

Why ?

@tt_su said:

Not that the API provides. You could extract to a temp file and read it.

I'm not sure how I am supposed to extract the image to a file, if I cannot read its data.

Any work around ?

In the Sketchup c++ SDK:

What is the equivalent of SUTextureGetImageData for a SUImageRef? How can I access images pixel data?

Thank you

Thank you, I fixed my problem by processing only materials used in the model:

aMat = Sketchup.active_model.materials.current
if aMat != nil and Sketchup.active_model.materials.include?(aMat)
   ...
end

Can someone explains why this happens ?

test = Sketchup.active_model.materials.current
#<Sketchup;;Material;0x8a19480>
test2 = test.clone
#<Deleted Entity;0x8a19278>

I'd like to store a material in a class variable to use it later, if I do not clone, and the selection change, test will not contain the previous material I want, but the new one selected.

Thank you