Merge pull request #28463 from mantidproject/28436_indirect_workbench_slowdown

IndirectReduction GUI slowing processing on workbench when open.

docs/source/release/v5.1.0/indirect_geometry.rst

@@ -5,8 +5,9 @@ Indirect Geometry Changes
 .. contents:: Table of Contents
    :local:
 
-.. warning:: **Developers:** Sort changes under appropriate heading
-    putting new features at the top of the section, followed by
-    improvements, followed by bug fixes.
+Improvements
+############
+
+- An issue with IndirectDataReduction causing it to slow down processing when open has been resolved.
 
 :ref:`Release 5.1.0 <v5.1.0>`
\ No newline at end of file

qt/widgets/plotting/src/Mpl/ContourPreviewPlot.cpp

@@ -68,11 +68,15 @@ void ContourPreviewPlot::onWorkspaceRemoved(
   if (auto workspace =
           boost::dynamic_pointer_cast<MatrixWorkspace>(nf->object())) {
     // If the artist has already been removed, ignore.
+    bool workspaceRemoved = false;
     try {
-      m_canvas->gca<MantidAxes>().removeWorkspaceArtists(workspace);
+      workspaceRemoved =
+          m_canvas->gca<MantidAxes>().removeWorkspaceArtists(workspace);
     } catch (Mantid::PythonInterface::PythonException &) {
     }
-    m_canvas->draw();
+    if (workspaceRemoved) {
+      m_canvas->draw();
+    }
   }
 }
 
@@ -86,8 +90,9 @@ void ContourPreviewPlot::onWorkspaceReplaced(
           boost::dynamic_pointer_cast<MatrixWorkspace>(nf->oldObject())) {
     if (auto newWorkspace =
             boost::dynamic_pointer_cast<MatrixWorkspace>(nf->newObject())) {
-      m_canvas->gca<MantidAxes>().replaceWorkspaceArtists(newWorkspace);
-      m_canvas->draw();
+      if (m_canvas->gca<MantidAxes>().replaceWorkspaceArtists(newWorkspace)) {
+        m_canvas->draw();
+      }
     }
   }
 }