Module input_generation 

How much input and model change the tree has been handed since a frame drew it.

A widget is clean until something it reads changes. Most widgets say so themselves, by tracking what they hold and marking it dirty. The rest read what reaches them from outside themselves — an event they handled, a document revision their root synced — and paint it without keeping a flag of their own. These two readings are for them.

generation moves when input is delivered. A widget’s own fields stand still across an event it did not take up, so only drawings that read outside state go stale with it (crate::outside_paint): treating every cache as stale on input would cost the frames that copy what they keep on screen.

model moves when a model the tree reads changes. That reaches widgets through the sync pass, so a cache kept across it would hold a drawing from before the change: every cache drawn with it is stale.

A host also compares the generations its last drawn frame read against the current ones: a change handed to the tree after that frame makes the next one due, so what a widget repaints from it reaches the screen.

Functions

generation

The input generation now: draw a frame against it and keep that drawing only while it still reads the same.

model

The model generation now: a drawing kept from another one painted a document that has since changed.

note

Input reached the tree: an event was delivered.

note_model

A model the tree reads changed.