Be (somewhat more) consistent about the value of pi

Use M_PI (and friends), where possible, in favor of hand-coded
approximations of various (in)accuracies.  Where that's not available
(e.g. fragment shaders), use the same value that qmath.h uses for
M_PI, for consistency.  Replaced math.h with qmath.h in places that
defined a fall-back in case math.h omits it (it's not in the C++
standard, although M_PI is in POSIX); or removed this entirely where
it wasn't used.

Reworked some code to reduce the amount of arithmetic needed, in the
process; e.g. pulling common factors out of loops.  Revised an
example's doc to not waste time talking about using a six-sig-fig
value for pi (which we no longer do) - it really wasn't relevant, or
anything to be proud of; nor did the doc mention its later use.

Task-number: QTBUG-58083
Change-Id: I5a31e3a2b6a823b97a43209bed61a37b9aa6c05f
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 9 insertions, 12 deletions

diff --git a/examples/widgets/graphicsview/elasticnodes/edge.cpp b/examples/widgets/graphicsview/elasticnodes/edge.cpp
index d9e4c62e34..aec12b4225 100644
--- a/examples/widgets/graphicsview/elasticnodes/edge.cpp
+++ b/examples/widgets/graphicsview/elasticnodes/edge.cpp
@@ -51,12 +51,9 @@
 #include "edge.h"
 #include "node.h"
 
-#include <cmath>
-
+#include <qmath.h>
 #include <QPainter>
 
-static const double Pi = 3.14159265358979323846264338327950288419717;
-
 //! [0]
 Edge::Edge(Node *sourceNode, Node *destNode)
     : arrowSize(10)
@@ -140,14 +137,14 @@ void Edge::paint(QPainter *painter, const QStyleOptionGraphicsItem *, QWidget *)
     // Draw the arrows
     double angle = std::atan2(-line.dy(), line.dx());
 
-    QPointF sourceArrowP1 = sourcePoint + QPointF(sin(angle + Pi / 3) * arrowSize,
-                                                  cos(angle + Pi / 3) * arrowSize);
-    QPointF sourceArrowP2 = sourcePoint + QPointF(sin(angle + Pi - Pi / 3) * arrowSize,
-                                                  cos(angle + Pi - Pi / 3) * arrowSize);
-    QPointF destArrowP1 = destPoint + QPointF(sin(angle - Pi / 3) * arrowSize,
-                                              cos(angle - Pi / 3) * arrowSize);
-    QPointF destArrowP2 = destPoint + QPointF(sin(angle - Pi + Pi / 3) * arrowSize,
-                                              cos(angle - Pi + Pi / 3) * arrowSize);
+    QPointF sourceArrowP1 = sourcePoint + QPointF(sin(angle + M_PI / 3) * arrowSize,
+                                                  cos(angle + M_PI / 3) * arrowSize);
+    QPointF sourceArrowP2 = sourcePoint + QPointF(sin(angle + M_PI - M_PI / 3) * arrowSize,
+                                                  cos(angle + M_PI - M_PI / 3) * arrowSize);
+    QPointF destArrowP1 = destPoint + QPointF(sin(angle - M_PI / 3) * arrowSize,
+                                              cos(angle - M_PI / 3) * arrowSize);
+    QPointF destArrowP2 = destPoint + QPointF(sin(angle - M_PI + M_PI / 3) * arrowSize,
+                                              cos(angle - M_PI + M_PI / 3) * arrowSize);
 
     painter->setBrush(Qt::black);
     painter->drawPolygon(QPolygonF() << line.p1() << sourceArrowP1 << sourceArrowP2);