Если вы используете qreal
(double
), то вы не должны терять точность. Если вы git grep float
в qtbase.git
, вы можете узнать немного больше:
dist/changes-5.2.0-****************************************************************************
dist/changes-5.2.0-* Important Behavior Changes *
dist/changes-5.2.0-****************************************************************************
dist/changes-5.2.0-
dist/changes-5.2.0- - Qt is now compiled with qreal typedef'ed to double on all
dist/changes-5.2.0: platforms. qreal was a float on ARM chipsets before. This guarantees more
dist/changes-5.2.0- consistent behavior between all platforms Qt supports, but is binary
dist/changes-5.2.0- incompatible to Qt 5.1 on ARM. The old behavior can be restored by
dist/changes-5.2.0: passing -qreal float to configure.
Интересно отметить, что в Qt, есть большие куски кода, которые перешли на использование только плавать:
commit 51d40d7e9bdfc63c5109aef5b732aa2ba10f985a
Author: Sean Harmer <[email protected]>
Date: Mon Aug 20 20:55:40 2012 +0100
Make gui/math3d classes use float rather than qreal
This corrects the mismatch between using floats for internal storage
and qreal in the API of QVector*D which leads to lots of implicit
casts between double and float.
This change also stops users from being surprised by the loss of
precision when using these classes on desktop platforms and removes
the need for the private constructors taking a dummy int as the final
argument.
The QMatrix4x4 and QQuaternion classes have been changed to use float
for their internal storage since these are meant to be used in
conjunction with the QVector*D classes. This is to prevent unexpected
loss of precision and to improve performance.
The on-disk format has also been changed from double to float thereby
reducing the storage required when streaming vectors and matrices. This
is potentially a large saving when working with complex 3D meshes etc.
This also has a significant performance improvement when passing
matrices to QOpenGLShaderProgram (and QGLShaderProgram) as we no
longer have to iterate and convert the data to floats. This is
an operation that could easily be needed many times per frame.
This change also opens the door for further optimisations of these
classes to be implemented by using SIMD intrinsics.
Как говорится, это должно было избежать неожиданной потери точности, поскольку функции принимали qreal
(double
), но сохраняли свои данные как float
. Если вы используете qreal
везде в своем собственном коде, у вас не будет этой проблемы.
Другая причина - выступление. Я не могу слишком много комментировать это, но я бы сказал, что для QT более важно оптимизировать такие вещи, как для пользователей пользователей Qt.
Вы можете найти описание [здесь] (http://doc.qt.io/qt-5/qtqml-cppintegration-data.html#basic-qt-data-types) –