Qwt 6.0.1 Support

Upgrade to QWT 6.0.1, but still uses a locally patched copy
since support for 8 axes has not been included, despite it
being a relatively simple patch.

Fixes #634.
Fixes #567.

qwt/examples/refreshtest/circularbuffer.cpp

@@ -0,0 +1,73 @@
+#include "circularbuffer.h"
+#include <math.h>
+
+CircularBuffer::CircularBuffer(double interval, size_t numPoints):
+    d_y(NULL),
+    d_referenceTime(0.0),
+    d_startIndex(0),
+    d_offset(0.0)
+{
+    fill(interval, numPoints);
+}
+
+void CircularBuffer::fill(double interval, size_t numPoints)
+{
+    if ( interval <= 0.0 || numPoints < 2 )
+        return;
+
+    d_values.resize(numPoints);
+    d_values.fill(0.0);
+
+    if ( d_y )
+    {
+        d_step = interval / (numPoints - 2);
+        for ( size_t i = 0; i < numPoints; i++ )
+            d_values[i] = d_y(i * d_step);
+    }
+
+    d_interval = interval;
+}
+
+void CircularBuffer::setFunction(double(*y)(double))
+{
+    d_y = y;
+}
+
+void CircularBuffer::setReferenceTime(double timeStamp)
+{
+    d_referenceTime = timeStamp;
+
+    const double startTime = ::fmod(d_referenceTime, d_values.size() * d_step);
+
+    d_startIndex = int(startTime / d_step); // floor
+    d_offset = ::fmod(startTime, d_step);
+}
+
+double CircularBuffer::referenceTime() const
+{
+    return d_referenceTime;
+}
+
+size_t CircularBuffer::size() const
+{
+    return d_values.size();
+}
+
+QPointF CircularBuffer::sample(size_t i) const
+{
+    const int size = d_values.size();
+
+    int index = d_startIndex + i;
+    if ( index >= size )
+        index -= size;
+
+    const double x = i * d_step - d_offset - d_interval;
+    const double y = d_values.data()[index];
+
+    return QPointF(x, y);
+}
+
+QRectF CircularBuffer::boundingRect() const
+{
+    return QRectF(-1.0, -d_interval, 2.0, d_interval);
+}