BUG: Fix segment disappearing when sharing segment editor node betwee…

…n widgets

When a single vtkMRMLSegmentEditorNode was used by multiple qSlicerSegmentEditorWidget instances then after using Threshold effect, the current segment disappeared from slice views.

The reason was that Threshold effects in every segment editor widgets get activated (via sharing the segment editor node) and they all started preview, saved original segment opacity, and then on "Apply" restored the original segment opacity.
However, the segment opacity that was restored by second, third, etc. effects were not the original anymore, but it was already the opacity that was set to 0 (it has to be set to 0 to prevent the current segment occluding the preview).

The solution could have been to store the original opacity in a shared location (e.g., in the segment editor node), but that would not have solved the slight rendering issue (preview glow was darker) and performance degradation caused by several effects showing the preview glow at the same time.

Fixed it by storing the object ID of the threshold effect that manipulates the segmentation display node in the node's "SegmentEditor.PreviewingEffect" attribute. All other Threshold effects check this attribute and if they find that another effect already provide preview then they don't display the preview.

This commit also fixes disappearing segment when selecting another segmentation node while the Threshold effect is active.

fixes #6874

Modules/Loadable/Segmentations/EditorEffects/Python/SegmentEditorEffects/SegmentEditorThresholdEffect.py

@@ -27,6 +27,7 @@ def __init__(self, scriptedEffect):
 
         self.segment2DFillOpacity = None
         self.segment2DOutlineOpacity = None
+        self.previewedSegmentationDisplayNode = None
         self.previewedSegmentID = None
 
         # Effect-specific members
@@ -42,7 +43,6 @@ def __init__(self, scriptedEffect):
 
         self.previewPipelines = {}
         self.histogramPipeline = None
-        self.setupPreviewDisplay()
 
         # Histogram stencil setup
         self.stencil = vtk.vtkPolyDataToImageStencil()
@@ -84,24 +84,24 @@ def helpText(self):
 </ul><p>""")
 
     def activate(self):
-        self.setCurrentSegmentTransparent()
-
         # Update intensity range
         self.sourceVolumeNodeChanged()
 
-        # Setup and start preview pulse
-        self.setupPreviewDisplay()
+        # Start preview pulse
         self.timer.start(200)
 
     def deactivate(self):
+        # Stop preview pulse
+        self.timer.stop()
+
         self.restorePreviewedSegmentTransparency()
 
-        # Clear preview pipeline and stop timer
-        self.clearPreviewDisplay()
+        # Clear preview pipeline
+        self.clearPreviewDisplayPipelines()
         self.clearHistogramDisplay()
-        self.timer.stop()
 
-    def setCurrentSegmentTransparent(self):
+
+    def updatePreviewedSegmentTransparency(self):
         """Save current segment opacity and set it to zero
         to temporarily hide the segment so that threshold preview
         can be seen better.
@@ -110,44 +110,53 @@ def setCurrentSegmentTransparent(self):
         opacity.
         """
         segmentationNode = self.scriptedEffect.parameterSetNode().GetSegmentationNode()
-        if not segmentationNode:
-            return
-        displayNode = segmentationNode.GetDisplayNode()
-        if not displayNode:
-            return
+        displayNode = segmentationNode.GetDisplayNode() if segmentationNode else None
         segmentID = self.scriptedEffect.parameterSetNode().GetSelectedSegmentID()
 
-        if segmentID == self.previewedSegmentID:
+        if (self.previewedSegmentationDisplayNode == displayNode) and (segmentID == self.previewedSegmentID):
             # already previewing the current segment
             return
 
         # If an other segment was previewed before, restore that.
         if self.previewedSegmentID:
             self.restorePreviewedSegmentTransparency()
 
+        if not segmentID:
+            # No segment selected, no need to make any segment transparent
+            return
+
+        # To allow previewing results, temporarily change opacity of the edited segment by modifying the display node.
+        # There may be multiple segment editor widgets that edit the same segmentation display node, therefore
+        # before we modify it we need to check if it is not used by any other segment editor effect.
+        currentEffectHash = str(self.__hash__())
+        previewingEffectHash = displayNode.GetAttribute("SegmentEditor.PreviewingEffect")
+        if previewingEffectHash and (previewingEffectHash != currentEffectHash):
+            # Another effect is already using this display node for preview
+            return
+
+        # Indicate in the display node that other segment editor effects should not tart preview now
+        displayNode.SetAttribute("SegmentEditor.PreviewingEffect", currentEffectHash)
+
         # Make current segment fully transparent
-        if segmentID:
-            self.segment2DFillOpacity = displayNode.GetSegmentOpacity2DFill(segmentID)
-            self.segment2DOutlineOpacity = displayNode.GetSegmentOpacity2DOutline(segmentID)
-            self.previewedSegmentID = segmentID
-            displayNode.SetSegmentOpacity2DFill(segmentID, 0)
-            displayNode.SetSegmentOpacity2DOutline(segmentID, 0)
+        self.segment2DFillOpacity = displayNode.GetSegmentOpacity2DFill(segmentID)
+        self.segment2DOutlineOpacity = displayNode.GetSegmentOpacity2DOutline(segmentID)
+        self.previewedSegmentID = segmentID
+        self.previewedSegmentationDisplayNode = displayNode
+        displayNode.SetSegmentOpacity2DFill(segmentID, 0)
+        displayNode.SetSegmentOpacity2DOutline(segmentID, 0)
 
     def restorePreviewedSegmentTransparency(self):
         """Restore previewed segment's opacity that was temporarily
-        made transparen by calling setCurrentSegmentTransparent().
+        made transparent by calling updatePreviewedSegmentTransparency().
         """
-        segmentationNode = self.scriptedEffect.parameterSetNode().GetSegmentationNode()
-        if not segmentationNode:
-            return
-        displayNode = segmentationNode.GetDisplayNode()
+        displayNode = self.previewedSegmentationDisplayNode
         if not displayNode:
             return
-        if not self.previewedSegmentID:
-            # already previewing the current segment
-            return
-        displayNode.SetSegmentOpacity2DFill(self.previewedSegmentID, self.segment2DFillOpacity)
-        displayNode.SetSegmentOpacity2DOutline(self.previewedSegmentID, self.segment2DOutlineOpacity)
+        if self.previewedSegmentID:
+            displayNode.SetSegmentOpacity2DFill(self.previewedSegmentID, self.segment2DFillOpacity)
+            displayNode.SetSegmentOpacity2DOutline(self.previewedSegmentID, self.segment2DOutlineOpacity)
+        displayNode.RemoveAttribute("SegmentEditor.PreviewingEffect")
+        self.previewedSegmentationDisplayNode = None
         self.previewedSegmentID = None
 
     def setupOptionsFrame(self):
@@ -413,7 +422,7 @@ def sourceVolumeNodeChanged(self):
                 self.scriptedEffect.setParameter("MaximumThreshold", hi)
 
     def layoutChanged(self):
-        self.setupPreviewDisplay()
+        self.updatePreviewDisplayPipelines()
 
     def setMRMLDefaults(self):
         self.scriptedEffect.setParameterDefault("MinimumThreshold", 0.0)
@@ -630,7 +639,7 @@ def onApply(self):
         # De-select effect
         self.scriptedEffect.selectEffect("")
 
-    def clearPreviewDisplay(self):
+    def clearPreviewDisplayPipelines(self):
         for sliceWidget, pipeline in self.previewPipelines.items():
             self.scriptedEffect.removeActor2D(sliceWidget, pipeline.actor)
         self.previewPipelines = {}
@@ -641,52 +650,64 @@ def clearHistogramDisplay(self):
         self.histogramPipeline.removeActors()
         self.histogramPipeline = None
 
-    def setupPreviewDisplay(self):
+    def updatePreviewDisplayPipelines(self):
         # Clear previous pipelines before setting up the new ones
-        self.clearPreviewDisplay()
-
         layoutManager = slicer.app.layoutManager()
-        if layoutManager is None:
-            return
+        sliceViewNames = layoutManager.sliceViewNames() if self.previewedSegmentationDisplayNode and layoutManager else []
 
         # Add a pipeline for each 2D slice view
-        for sliceViewName in layoutManager.sliceViewNames():
+        sliceWidgetPipelinesToKeep = []
+        for sliceViewName in sliceViewNames:
+
             sliceWidget = layoutManager.sliceWidget(sliceViewName)
             if not self.scriptedEffect.segmentationDisplayableInView(sliceWidget.mrmlSliceNode()):
+                # No need to add pipeline in this widget
+                continue
+
+            sliceWidgetPipelinesToKeep.append(sliceWidget)
+            pipeline = self.previewPipelines.get(sliceWidget)
+            if pipeline:
+                # Pipeline is already present
                 continue
+
+            # Add pipeline
             renderer = self.scriptedEffect.renderer(sliceWidget)
             if renderer is None:
-                logging.error("setupPreviewDisplay: Failed to get renderer!")
+                logging.error("updatePreviewDisplayPipelines: Failed to get renderer!")
                 continue
-
-            # Create pipeline
             pipeline = PreviewPipeline()
             self.previewPipelines[sliceWidget] = pipeline
-
-            # Add actor
             self.scriptedEffect.addActor2D(sliceWidget, pipeline.actor)
 
+        # Removed unused pipelines
+        for sliceWidget, pipeline in self.previewPipelines.items():
+            if sliceWidget in sliceWidgetPipelinesToKeep:
+                continue
+            self.scriptedEffect.removeActor2D(sliceWidget, pipeline.actor)
+            self.previewPipelines.pop(sliceWidget)
+
     def preview(self):
+        # Make sure we keep the currently selected segment hidden
+        # (the user may have changed selected segmentation or segment)
+        self.updatePreviewedSegmentTransparency()
+
+        # Update preview display pipelines
+        if self.previewedSegmentationDisplayNode and not self.previewPipelines:
+            self.updatePreviewDisplayPipelines()
+        elif not self.previewedSegmentationDisplayNode and self.previewPipelines:
+            self.clearPreviewDisplayPipelines()
+
+        if not self.previewedSegmentationDisplayNode:
+            return
+
         opacity = 0.5 + self.previewState / (2.0 * self.previewSteps)
         min = self.scriptedEffect.doubleParameter("MinimumThreshold")
         max = self.scriptedEffect.doubleParameter("MaximumThreshold")
 
         # Get color of edited segment
-        segmentationNode = self.scriptedEffect.parameterSetNode().GetSegmentationNode()
-        if not segmentationNode:
-            # scene was closed while preview was active
-            return
-        displayNode = segmentationNode.GetDisplayNode()
-        if displayNode is None:
-            logging.error("preview: Invalid segmentation display node!")
-            color = [0.5, 0.5, 0.5]
         segmentID = self.scriptedEffect.parameterSetNode().GetSelectedSegmentID()
 
-        # Make sure we keep the currently selected segment hidden (the user may have changed selection)
-        if segmentID != self.previewedSegmentID:
-            self.setCurrentSegmentTransparent()
-
-        r, g, b = segmentationNode.GetSegmentation().GetSegment(segmentID).GetColor()
+        r, g, b = self.previewedSegmentationDisplayNode.GetSegmentColor(segmentID)
 
         # Set values to pipelines
         for sliceWidget in self.previewPipelines:
@@ -707,6 +728,16 @@ def preview(self):
     def processInteractionEvents(self, callerInteractor, eventId, viewWidget):
         abortEvent = False
 
+        if viewWidget not in self.previewPipelines:
+            # In this view, this effect instance does not display threshold preview pipeline,
+            # therefore prevent it from displaying the local histogram pipeline, too.
+            return abortEvent
+
+        # Note that if multiple segment editor widgets are active then only one (the first that gets the interaction events)
+        # will be notified. In all the other segment editor widgets the local histogram will not be updated.
+        # The behavior could be made more deterministic by storing a preferred segment editor node in the selection node
+        # and not using the same segment editor node in multiple segment editor widgets.
+
         masterImageData = self.scriptedEffect.sourceVolumeImageData()
         if masterImageData is None:
             return abortEvent