Merge pull request #840 from OE-FET/patch-3

Clipping: don't assume that x-values have uniform spacing

pyqtgraph/graphicsItems/PlotDataItem.py

@@ -542,13 +542,26 @@ class PlotDataItem(GraphicsObject):
             if self.opts['clipToView']:
                 view = self.getViewBox()
                 if view is None or not view.autoRangeEnabled()[0]:
-                    # this option presumes that x-values have uniform spacing
+                    # this option presumes that x-values are in increasing order
                     range = self.viewRect()
                     if range is not None and len(x) > 1:
+                        # clip to visible region extended by downsampling value, assuming
+                        # uniform spacing of x-values, has O(1) performance
                         dx = float(x[-1]-x[0]) / (len(x)-1)
-                        # clip to visible region extended by downsampling value
+                        x0 = np.clip(int((range.left()-x[0])/dx) - 1*ds, 0, len(x)-1)
-                        x0 = np.clip(int((range.left()-x[0])/dx)-1*ds , 0, len(x)-1)
+                        x1 = np.clip(int((range.right()-x[0])/dx) + 2*ds, 0, len(x)-1)
-                        x1 = np.clip(int((range.right()-x[0])/dx)+2*ds , 0, len(x)-1)
+                        
+                        # if data has been clipped too strongly (in case of non-uniform 
+                        # spacing of x-values), refine the clipping region as required
+                        # worst case performance: O(log(n))
+                        # best case performance: O(1)
+                        if x[x0] > range.left():
+                            x0 = np.searchsorted(x, range.left()) - 1*ds
+                            x0 = np.clip(x0, a_min=0, a_max=len(x))
+                        if x[x1] < range.right():
+                            x1 = np.searchsorted(x, range.right()) + 2*ds
+                            x1 = np.clip(x1, a_min=0, a_max=len(x))
+                    
                         x = x[x0:x1]
                         y = y[x0:x1]
                     

pyqtgraph/graphicsItems/tests/test_PlotDataItem.py

@@ -64,3 +64,25 @@ def test_clear_in_step_mode():
     c = pg.PlotDataItem([1,4,2,3], [5,7,6], stepMode=True)
     w.addItem(c)
     c.clear()
+
+def test_clipping():
+    y = np.random.normal(size=150)
+    x = np.exp2(np.linspace(5, 10, 150))  # non-uniform spacing
+
+    w = pg.PlotWidget(autoRange=True, downsample=5)
+    c = pg.PlotDataItem(x, y)
+    w.addItem(c)
+    w.show()
+
+    c.setClipToView(True)
+
+    w.setXRange(200, 600)
+
+    for x_min in range(100, 2**10 - 100, 100):
+        w.setXRange(x_min, x_min + 100)
+
+        xDisp, _ = c.getData()
+        vr = c.viewRect()
+
+        assert xDisp[0] <= vr.left()
+        assert xDisp[-1] >= vr.right()