Set default QGraphicsTransform3D axis to (0, 0, 1)

The docs said that the default axis was (0, 0, 1), but the code
and unit tests were using (0, 0, 0).  Modify the code to match the
docs because (0, 0, 0) is not very useful.  Also optimize the
calculation of sin/cos values for 90, 180, and 270 degrees.

Reviewed-by: Aaron Kennedy

1 files changed, 26 insertions, 11 deletions

diff --git a/src/gui/graphicsview/qgraphicstransform.cpp b/src/gui/graphicsview/qgraphicstransform.cpp
index 778cd94..ae88641 100644
--- a/src/gui/graphicsview/qgraphicstransform.cpp
+++ b/src/gui/graphicsview/qgraphicstransform.cpp
@@ -80,11 +80,7 @@
 #include "qgraphicsitem_p.h"
 #include "qgraphicstransform_p.h"
 #include <QDebug>
-
-#include <math.h>
-#ifndef M_PI
-#define M_PI 3.14159265358979323846
-#endif
+#include <QtCore/qmath.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -355,7 +351,6 @@ public:
     QGraphicsRotationPrivate()
             : angle(0) {}
     QPointF origin;
-    qreal originY;
     qreal angle;
 };
 
@@ -475,13 +470,18 @@ void QGraphicsRotation::applyTo(QTransform *t) const
     By default the axis is (0, 0, 1), giving QGraphicsRotation3D the same
     default behavior as QGraphicsRotation (i.e., rotation around the Z axis).
 
+    Note: the final rotation is the combined effect of a rotation in
+    3D space followed by a projection back to 2D.  If several rotations
+    are performed in succession, they will not behave as expected unless
+    they were all around the Z axis.
+
     \sa QGraphicsTransform, QGraphicsItem::setRotation(), QTransform::rotate()
 */
 
 class QGraphicsRotation3DPrivate : public QGraphicsRotationPrivate
 {
 public:
-    QGraphicsRotation3DPrivate() {}
+    QGraphicsRotation3DPrivate() : axis(0, 0, 1) {}
 
     QVector3D axis;
 };
@@ -526,6 +526,7 @@ void QGraphicsRotation3D::setAxis(const QVector3D &axis)
     update();
 }
 
+const qreal deg2rad = qreal(0.017453292519943295769);        // pi/180
 static const qreal inv_dist_to_plane = 1. / 1024.;
 
 /*!
@@ -535,13 +536,27 @@ void QGraphicsRotation3D::applyTo(QTransform *t) const
 {
     Q_D(const QGraphicsRotation3D);
 
-    if (d->angle == 0. ||
+    qreal a = d->angle;
+
+    if (a == 0. ||
         (d->axis.z() == 0. && d->axis.y() == 0 && d->axis.x() == 0))
         return;
 
-    qreal rad = d->angle * 2. * M_PI / 360.;
-    qreal c = ::cos(rad);
-    qreal s = ::sin(rad);
+    qreal c, s;
+    if (a == 90. || a == -270.) {
+        s = 1.;
+        c = 0.;
+    } else if (a == 270. || a == -90.) {
+        s = -1.;
+        c = 0.;
+    } else if (a == 180.) {
+        s = 0.;
+        c = -1.;
+    } else {
+        qreal b = deg2rad*a;
+        s = qSin(b);
+        c = qCos(b);
+    }
 
     qreal x = d->axis.x();
     qreal y = d->axis.y();