Doc: Improve QTransform documentation

* Explain QTransform's model of vector/matrix operations. * Improve snippets used to illuminate QTransform's behavior. Fixes: QTBUG-83869 Pick-to: 6.2 6.1 5.15 Change-Id: I84c3b1a221c139ee992f82c3ee4aebadeef8ee63 Reviewed-by: Edward Welbourne <edward.welbourne@qt.io> Reviewed-by: Topi Reiniö <topi.reinio@qt.io> Reviewed-by: Andy Nichols <andy.nichols@qt.io> 

1 files changed, 6 insertions, 8 deletions

diff --git a/src/gui/doc/snippets/transform/main.cpp b/src/gui/doc/snippets/transform/main.cpp
index f3b31b0f839..d15b0590207 100644
--- a/src/gui/doc/snippets/transform/main.cpp
+++ b/src/gui/doc/snippets/transform/main.cpp
@@ -48,6 +48,7 @@
 **
 ****************************************************************************/
 #include <QApplication>
+#include <QMath>
 #include <QPainter>
 #include <QVBoxLayout>
 #include <QWidget>
@@ -105,18 +106,15 @@ class BasicOperations : public QWidget
 //! [2]
 void BasicOperations::paintEvent(QPaintEvent *)
 {
- double pi = 3.14;
-
- double a = pi/180 * 45.0;
+ const double a = qDegreesToRadians(45.0);
 double sina = sin(a);
 double cosa = cos(a);

- QTransform translationTransform(1, 0, 0, 1, 50.0, 50.0);
- QTransform rotationTransform(cosa, sina, -sina, cosa, 0, 0);
- QTransform scalingTransform(0.5, 0, 0, 1.0, 0, 0);
+ QTransform scale(0.5, 0, 0, 1.0, 0, 0);
+ QTransform rotate(cosa, sina, -sina, cosa, 0, 0);
+ QTransform translate(1, 0, 0, 1, 50.0, 50.0);

- QTransform transform;
- transform = scalingTransform * rotationTransform * translationTransform;
+ QTransform transform = scale * rotate * translate;

 QPainter painter(this);
 painter.setPen(QPen(Qt::blue, 1, Qt::DashLine));