There has a the difference about QTransform between qt5 and qt6, How can I do?

[hidxl]

I created a scene (QGraphicsScene) with a range of (-360,-360,720,720), then created an item on the scene that represents a layer, and then created an item whose parent is a layeritem.
Finally, through debugging, it is found that the device matrix of item is QTransform(0.0, 9.2370219841123224e-07, 0.0,
-9.2370219841123224e-07, 0.0, 0.0,
117.01799774169922, -36.503170013427734, 1.0)

In this QTransform, QT5 can click on the item normally, but not under QT6.

QT5 is considered this QTransform invertible, but QT6 is NOT .
the return value of "ok" QT5 is TRURE but QT6 is FALSE
Here's the test code:

auto powertransform =  QTransform(0.0, 9.2370219841123224e-07, 0.0,
-9.2370219841123224e-07, 0.0, 0.0,
117.01799774169922, -36.503170013427734, 1.0);
bool ok(false);
auto newtr= powertransform.inverted(&ok);

[SGaist]

Hi and welcome to devnet,

Which version of Qt are you using ?
Can you provide a minimal compilable example just to be sure that everybody can reproduce the failure the same way as you ?

[Christian Ehrlicher]

Nothing changed in between here - a QTransform can be inverted when the determinant is not 0 Your determinant is near zero (8.53226e-13) but not completely. Maybe you used float in Qt5 so it is 0 or a special compiler flags which uses precise math or whatever.

/edit: changed from 'is 0' to 'is not 0'

[JohanSolo]

@Christian-Ehrlicher said in There has a the difference about QTransform between qt5 and qt6, How can I do?:

a QTransform can be inverted when the determinant is 0 Your determinant is near zero (8.53226e-13) but not completely. Maybe you used float in Qt5 so it is 0 or a special compiler flags which uses precise math or whatever.

Pardon me to add my two cents, but a transformation can be inverted if and only if its determinant is different from zero, otherwise it is called a singular matrix and cannot be inverted.

[JonB]

@JohanSolo
I think you should provide the following information:

• What version of Qt5 which behaves "well" do you use?
• What version of Qt6 which performs "badly" do you use?
• What platform are you on?
• What compiler do you use?
• What exact flags are passed to compiler in both cases?
• Can you provide a complete program in a few lines of code which illustrates your issue?

[Christian Ehrlicher]

@JohanSolo said in There has a the difference about QTransform between qt5 and qt6, How can I do?:

if and only if its determinant is different from zero,

Yeah, forgot the not, thx & fixed