Re: Size allocation and redrawing issues

[Tim Janik <timj gtk org>]

On 3 Nov 2001, Owen Taylor wrote:

> There are some issues here we need to think through in terms
> of how requisition and allocation relate to the state of
> widgets, in particular to it being:
> 
>  - Parent set 
>  - Anchored
>  - Realized 
>  - style ensured
>  - visible
>  - mapped
>  - viewable (anchored and all parents visible)
> 
> In terms of requisition, there are basically three conditions:
> 
>  R1) "requisition not meaingful"
>  R2) "requisition meaingful, but we don't put the widget
>     in the resize queue for resize if it changes"
>  R3) "We update the requisition through the resize queue"
> 
> For allocation, the conditions are:
> 
>  A1) We can't call size_allocate()
>  A2) We can call size_allocate()
>  A3) "We update the requisition through the resize queue"
> 
> I believe that the conditions are:
> 
>  R1,A1)
>  R2,A2) Widget is anchored (note that to call size_request()
>         we need to ensure the style, but that can be done
>         at any point when the widget is anchored)
>  R3,A3) Widget is viewable
> 
> So, it seems to me that the corresponding flag/resize queue
> requirements are only:
> 
>  R1 => R2 : Set ALLOC_NEEDED, RESIZE_NEEDED
>  R2 => R3 : If ALLOC_NEEDED or RESIZE_NEEDED is set queue
>             for resize
> 
> (the current logic isn't really close to this, though I
> think it works out that from R1=>R3 we will set ALLOC_NEEDED
> and RESIZE_NEEDED and queue for resize)
> 
> On the reverse transitions:
> 
>  R3 => R2 : "Unqueue for resize" isn't needed since 
>             parent widgets won't allocate non-visible
>             children.
>  R2 => R1 : "Clear ALLOC_NEEDED RESIZE_NEEDED" flags. Not  
>             necessary since the flags are meaningless
>             in R1. 

i don't quite agree with the rest here.
for viewable widgets, ALLOC_NEEDED/RESIZE_NEEDED always means that
the widget either is queued for a resize, or has a container that
is queued for a resize (your code relies on that, e.g. when walking
up widget->parent in a loop and breaks on a parent that has ALLOC_NEEDED/
RESIZE_NEEDED set on it).
so as a result, i'd say that non-viewable widets should never have
any of those flags set, if we don't honour that, we'll mess up things
earlier or later and introduce subtle to track bugs.

> 
> Regards,
>                                         Owen
> 

---
ciaoTJ