title: how to hiden the unncessary lines or edges on the same complete plane when pyqtgraph displays a STL file
body: <p>I found a STL viewer program using pyqtgraph from <a href="https://github.com/Be4rR/STLViewer" rel="nofollow noreferrer">STLViewer</a><br />
  <a href="https://pyqtgraph.readthedocs.io/en/latest/style.html" rel="nofollow noreferrer">pyqtgraph document </a><br />
  the key parameters are set as</p>
  <pre><code># color is a tuple in the form RGBA  (0.4,0.9,0.6,1)`
  mesh = gl.GLMeshItem(meshdata=meshdata, smooth=True, drawEdges=True, drawFaces=True,  shader='balloon',color= (0.4,0.9,0.6,1))
  </code></pre>
  <p>a stl file appearance displays as the following</p>
  <p><a href="https://i.stack.imgur.com/8jJiu.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8jJiu.png" alt="enter image description here" /></a></p>
  <p>This appearance is not I want, since it displays many edges even though on the same complete plane.</p>
  <p>and if set <code>drawEdges=False</code> then it displays as</p>
  <p><a href="https://i.stack.imgur.com/DPrSD.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/DPrSD.png" alt="enter image description here" /></a></p>
  <p>However, the concrete edges I can touch are also hidden, this is not I want too.</p>
  <p>What I want is like this</p>
  <p><a href="https://i.stack.imgur.com/IWGAg.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/IWGAg.png" alt="enter image description here" /></a></p>
  <p>this is painted by pyVTK</p>
  <p>the main  program is</p>
  <pre><code>import vtk
  reader = vtk.vtkSTLReader()
  reader.SetFileName(filename)
  mapper = vtk.vtkPolyDataMapper()  # maps polygonal data to graphics primitives
  mapper.SetInputConnection(reader.GetOutputPort())
  actor_0 = vtk.vtkLODActor()
  actor_0.SetMapper(mapper)
  actor_0.SetScale(1000, 1000, 1000)
  actor_0.GetProperty().SetDiffuseColor(0.4,0.9,0.6)
  actor_0.GetProperty().SetDiffuse(.8)
  actor_0.GetProperty().SetSpecular(.5)
  actor_0.GetProperty().SetSpecularColor(1.0, 1.0, 1.0)
  actor_0.GetProperty().SetSpecularPower(30.0)
  </code></pre>