Clarified situation regarding the absence of QwtClipper

Author: Pierre Raybaut

README

@@ -18,6 +18,12 @@ Licensed under the terms of the MIT License (see qwt/LICENSE)
         - QwtPicker
         - QwtPlotPicker
 
+      QwtClipper is not implemented yet (and it will probably be very difficult
+      or impossible to implement it in pure Python without performance issues).
+      As a consequence, when zooming in a plot curve, the entire curve is still
+      painted (in other words, when working with large amount of data, there is
+      no performance gain when zooming in).
+
     Dependencies
 
         Requirements

qwt/__init__.py

@@ -101,6 +101,3 @@ def setMinPen(self, *args):
                       RuntimeWarning)
         return self.setMinorPen(*args)
 ## ============================================================================
-
-
-#TODO: implement QwtClipper: needed for SVG export for example

qwt/clipper.py

@@ -1,5 +1,10 @@
 # -*- coding: utf-8 -*-
 
+from qwt.qt.QtGui import QPolygon, QPolygonF
+from qwt.qt.QtCore import QRect, QRectF
+
+import numpy as np
+
 
 class LeftEdge(object):
     def __init__(self, x1, x2, y1, y2):
@@ -68,8 +73,44 @@ def data(self):
 
     def operator(self, i):
         return self.m_buffer[i]
+
+
+class QwtPolygonClipper(object):
+    def __init__(self, clipRect):
+        self.__clipRect = clipRect
 
+    def clipPolygon(self, polygon, closePolygon):
+        if self.__clipRect.contains(polygon.boundingRect()):
+            return polygon
+        
 
 
 class QwtClipper(object):
-    pass
+    def __init__(self):
+        pass
+    
+    def clipPolygon(self, clipRect, polygon, closePolygon):
+        raise NotImplementedError("Nearly impossible to implement in pure Python")
+        #XXX: the only viable option would be to use Qt's intersected method 
+        # but unfortunately it's closing systematically the output polygon
+        # (how to test it: polygon.intersected(QPolygonF(clipRect)))
+        
+        if isinstance(clipRect, QRectF):
+            minX = np.ceil(clipRect.left())
+            maxX = np.floor(clipRect.right())
+            minY = np.ceil(clipRect.top())
+            maxY = np.floor(clipRect.bottom())
+            clipRect = QRect(minX, minY, maxX-minX, maxY-minY)
+        clipper = QwtPolygonClipper(clipRect)
+        return clipper.clipPolygon(polygon, closePolygon)
+    
+    def clipPolygonF(self, clipRect, polygon, closePolygon):
+        raise NotImplementedError("Nearly impossible to implement in pure Python")
+        #XXX: the only viable option would be to use Qt's intersected method 
+        # but unfortunately it's closing systematically the output polygon
+        # (how to test it: polygon.intersected(QPolygonF(clipRect)))
+        
+        if isinstance(clipRect, QRect):
+            clipRect = QRectF(clipRect)
+        clipper = QwtPolygonClipper(clipRect)
+        return clipper.clipPolygon(polygon, closePolygon)

qwt/painter.py

@@ -19,6 +19,8 @@
 def qwtIsClippingNeeded(painter):
     doClipping = False
     clipRect = QRectF()
+    #TODO: remove next line when QwtClipper will be implemented
+    return doClipping, clipRect
     pe = painter.paintEngine()
     if pe and pe.type() == QPaintEngine.SVG:
         if painter.hasClipping():
@@ -244,9 +246,9 @@ def drawPolygon(self, painter, polygon):
         cpa = polygon
         if deviceClipping:
             if isinstance(polygon, QPolygonF):
-                cpa = QwtClipper.clipPolygonF(clipRect, polygon)
+                cpa = QwtClipper().clipPolygonF(clipRect, polygon)
             else:
-                cpa = QwtClipper.clipPolygon(clipRect, polygon)
+                cpa = QwtClipper().clipPolygon(clipRect, polygon)
         painter.drawPolygon(cpa)
 
     def drawPolyline(self, *args):
@@ -256,9 +258,9 @@ def drawPolyline(self, *args):
             cpa = polygon
             if deviceClipping:
                 if isinstance(polygon, QPolygonF):
-                    cpa = QwtClipper.clipPolygonF(clipRect, polygon)
+                    cpa = QwtClipper().clipPolygonF(clipRect, polygon)
                 else:
-                    cpa = QwtClipper.clipPolygon(clipRect, polygon)
+                    cpa = QwtClipper().clipPolygon(clipRect, polygon)
             qwtDrawPolyline(painter, cpa, cpa.size(),
                             self.__polylineSplitting)
         elif len(args) == 3:
@@ -267,10 +269,10 @@ def drawPolyline(self, *args):
             if deviceClipping:
                 if isinstance(points[0], QPointF):
                     polygon = QPolygonF(points)
-                    polygon = QwtClipper.clipPolygonF(clipRect, polygon)
+                    polygon = QwtClipper().clipPolygonF(clipRect, polygon)
                 else:
                     polygon = QPolygon(points)
-                    polygon = QwtClipper.clipPolygon(clipRect, polygon)
+                    polygon = QwtClipper().clipPolygon(clipRect, polygon)
                 qwtDrawPolyline(painter, polygon,
                                 polygon.size(), self.__polylineSplitting)
 #                polygon = QPolygonF(pointCount)

qwt/plot_curve.py

@@ -51,9 +51,9 @@ def __init__(self):
         self.baseline = 0.
         self.symbol = None
         self.attributes = 0
-#        self.paintAttributes = QwtPlotCurve.ClipPolygons|QwtPlotCurve.FilterPoints
-        #TODO: uncomment previous line when QwtClipper will be implemented
         self.paintAttributes = QwtPlotCurve.FilterPoints
+        #TODO: uncomment next line when QwtClipper will be implemented
+#        self.paintAttributes = QwtPlotCurve.ClipPolygons|QwtPlotCurve.FilterPoints
         self.legendAttributes = QwtPlotCurve.LegendShowLine
         self.pen = QPen(Qt.black)
         self.brush = QBrush()