What is the semantics of Composite?

I always understood that the Composite module delivers one single bitmap or vector image, without any information on its input layers.

Consider the following layering: a bottom green layer is hidden by a top red layer. After compositing, the resulting image is red.

Now, after compositing, I use ‘render selected colours only’ for the colour Green, in a Colour Override module, that comes after Composite.

What I expect to see is an empty image, that is, the non-existing green from the red image. However, the result is green?

It looks like the Colour Override is done before the Composite?

Any clue?

According to Toon Boom Support, it is a little more complicated: the Color Override is processed before the Composite. If it is really the case that modules are not processed in network order, it makes it hard for users to understand the expected outcome.

I suggest Toon Boom clarifies this in their documentation.

The Bitmap composite will flatten the image at that point, and give out a bitmap as the resultant.

The Vector or Pass Through options, however, do not flatten. They retain the same information as before the composite. Effectively, what it does is just gathers the layers together for the purpose of performing tasks on multiple layers.