Fix QwtScaleMap rectangle transform and degenerate scale handling

* Stop inflating transformed rectangles by 1 unit
* Collapse degenerate scales (``s1 == s2``) to ``p1``

Author: PierreRaybaut

qwt/scale_map.py

@@ -217,8 +217,12 @@ def updateFactor(self):
         if self.__transform:
             self.__ts1 = self.__transform.transform(self.__ts1)
             ts2 = self.__transform.transform(ts2)
-        self.__cnv = 1.0
-        if self.__ts1 != ts2:
+        if self.__ts1 == ts2:
+            # Degenerate scale: collapse every value to ``p1`` (matches the
+            # symmetric guard in ``invTransform_scalar`` and the C++ Qwt
+            # behaviour).
+            self.__cnv = 0.0
+        else:
             self.__cnv = (self.__p2 - self.__p1) / (ts2 - self.__ts1)
 
     def transform(self, *args):
@@ -269,7 +273,7 @@ def transform(self, *args):
                 y1 = 0.0
             if qwtFuzzyCompare(y2, 0.0, y2 - y1) == 0:
                 y2 = 0.0
-            return QRectF(x1, y1, x2 - x1 + 1, y2 - y1 + 1)
+            return QRectF(x1, y1, x2 - x1, y2 - y1)
         else:
             raise TypeError(
                 "%s().transform() takes 1 or 3 argument(s) (%s "
@@ -292,8 +296,8 @@ def invTransform(self, *args):
         elif isinstance(args[2], QRectF):
             xMap, yMap, rect = args
             x1 = xMap.invTransform(rect.left())
-            x2 = xMap.invTransform(rect.right() - 1)
+            x2 = xMap.invTransform(rect.right())
             y1 = yMap.invTransform(rect.top())
-            y2 = yMap.invTransform(rect.bottom() - 1)
+            y2 = yMap.invTransform(rect.bottom())
             r = QRectF(x1, y1, x2 - x1, y2 - y1)
             return r.normalized()