[Interest] Replacement for Qt4 QMatrix4x4?

Christian Gagneraud chgans at gmail.com
Fri Feb 22 10:27:49 CET 2019

On Fri, 22 Feb 2019 at 19:34, Thiago Macieira <thiago.macieira at intel.com> wrote:
> On Thursday, 21 February 2019 13:47:05 PST Matthew Woehlke wrote:
> > (Uh...why? I am not particularly amused by the loss of precision, nor
> > the extremely subtle incompatibility.)
> Changed in commit 51d40d7e9bdfc63c5109aef5b732aa2ba10f985a:
> http://code.qt.io/cgit/qt/qtbase.git/commit/?
> id=51d40d7e9bdfc63c5109aef5b732aa2ba10f985a
> One of the two reasons the commit message says was to avoid the surprise in
> that it used float in embedded platforms (read: ARM). That rationale is no
> longer applicable, as we changed qreal to be double in all platforms about one
> year later: http://code.qt.io/cgit/qt/qtbase.git/commit/?
> id=d8bf317546bcfab0b6b50375218429fa9d470705

I don't know who's "we" in your sentence, but in mine "we" are still
configuring Qt5 with qreal=float for arm v5, v6 and v7.
The decision was taken after a performance assessment, and it was
deemed "worth it".
I'm not saying it is a good idea, i'm just saying that it brought
performance up. I as well speculate that we are likely to drop it with
arm v8.
If you do not want to support qreal=float anymore, please do not allow
./configure to make that choice and maybe get rid of qreal typedef,
and delete qreal from Qt6 API while you're at it.
Would you consider making arm v8 the minimum requirement for Qt6?


> I think we need to reconsider the storage type for Qt 6. Added to
> https://bugreports.qt.io/browse/QTBUG-62425
> --
> Thiago Macieira - thiago.macieira (AT) intel.com
>   Software Architect - Intel System Software Products
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