[Development] Behavior change: A sane and consistent QPainter coordinate system in Qt 5

Philip Ashmore contact at philipashmore.com
Fri Oct 12 01:44:24 CEST 2012

On 11/10/12 15:06, BRM wrote:
> ----- Original Message -----
>> From: Sorvig Morten<Morten.Sorvig at digia.com>
>> Subject: Re: [Development] Behavior change: A sane and consistent QPainter coordinate system in Qt 5
>> On Oct 11, 2012, at 1:57 PM, Samuel Rødal<samuel.rodal at digia.com>
>> wrote:
>>>   It's unfortunate to potentially cause some extra trouble for a subset
>> of
>>>   existing applications that wish to port to Qt 5, but weighed against the
>>>   utter embarrassment of the current fill rules I think we need this change.
>> +1 from me for "utter embarrassment".
>> A slight tangent, perhaps we should be less afraid of making behavioural changes
>> to Qt in minor releases, as long as they are flagged and old behaviour can be
>> restored. The flags could serve for say 3 minor releases and then be retired
>> together with the old code path. An even softer path could be to make changes
>> opt-in, then opt-out, and finally mandatory over the course of several minor
>> releases.
> How about opt-in (via configure or extra flags) until the next major release?
> I don't think doing the opt-in/opt-out/mandatory over several minor release would bode well for compatibility between minor releases, which is a big must.
This could in general be addressed with a "QT_LOOKS_LIKE=4.7.4" in 
/etc/profile, per user or per application.
Specific overrides could be opted in/out with "QT_COORDS_LOOKS_LIKE=5.0.0".

This could even be back-ported.

My 2c.

> For example, I have some software that is still running on Qt 4.5.1 in production; and component is running on Qt 4.7.4. Yet I need the behaviors in the overlapping code to be the same; without having to worry about getting the compilations right in both cases.
> Ben
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