Added python test as example for volume shader replacements

Rendering/Volume/Testing/Python/CMakeLists.txt

@@ -23,7 +23,9 @@ set (VolumeOpenGL2PythonTests
      gaussian.py
      TestGPURayCastIndependentComponent.py,NO_RT
      TestGPURayCastIndependentComponentMIP.py,NO_RT
-     TestGPURayCastIndependentComponentMinIP.py,NO_RT)
+     TestGPURayCastIndependentComponentMinIP.py,NO_RT
+     TestGPURayCastUserShader.py
+     )
 
 if ("${VTK_RENDERING_BACKEND}" STREQUAL "OpenGL2")
   vtk_add_test_python(

Rendering/Volume/Testing/Python/TestGPURayCastUserShader.py

+#!/usr/bin/env python
+'''
+=========================================================================
+
+  Program:   Visualization Toolkit
+  Module:    TestGPURayCastUserShader.py
+
+  Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
+  All rights reserved.
+  See Copyright.txt or http:#www.kitware.com/Copyright.htm for details.
+
+     This software is distributed WITHOUT ANY WARRANTY without even
+     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+     PURPOSE.  See the above copyright notice for more information.
+
+=========================================================================
+'''
+
+import sys
+import vtk
+import vtk.test.Testing
+from vtk.util.misc import vtkGetDataRoot
+VTK_DATA_ROOT = vtkGetDataRoot()
+
+'''
+  Prevent .pyc files from being created.
+  Stops the vtk source being polluted
+  by .pyc files.
+'''
+sys.dont_write_bytecode = True
+
+dataRoot = vtkGetDataRoot()
+reader = vtk.vtkNrrdReader()
+reader.SetFileName("" + str(dataRoot) + "/Data/tooth.nhdr")
+reader.Update()
+
+volumeProperty = vtk.vtkVolumeProperty()
+volumeProperty.ShadeOn()
+volumeProperty.SetInterpolationType(vtk.VTK_LINEAR_INTERPOLATION)
+
+range = reader.GetOutput().GetScalarRange()
+
+# Prepare 1D Transfer Functions
+ctf = vtk.vtkColorTransferFunction()
+ctf.AddRGBPoint(0, 0.0, 0.0, 0.0)
+ctf.AddRGBPoint(510, 0.4, 0.4, 1.0)
+ctf.AddRGBPoint(640, 1.0, 1.0, 1.0)
+ctf.AddRGBPoint(range[1], 0.9, 0.1, 0.1)
+
+pf = vtk.vtkPiecewiseFunction()
+pf.AddPoint(0, 0.00)
+pf.AddPoint(510, 0.00)
+pf.AddPoint(640, 0.5)
+pf.AddPoint(range[1], 0.4)
+
+volumeProperty.SetScalarOpacity(pf)
+volumeProperty.SetColor(ctf)
+volumeProperty.SetShade(1)
+
+mapper = vtk.vtkOpenGLGPUVolumeRayCastMapper()
+mapper.SetInputConnection(reader.GetOutputPort())
+mapper.SetUseJittering(1)
+
+# Modify the shader to color based on the depth of the translucent voxel
+mapper.AddShaderReplacement(
+    vtk.vtkShader.Fragment,  # Replace in the fragment shader
+    "//VTK::Base::Dec",      # Source string to replace
+    True,                    # before the standard replacements
+    "//VTK::Base::Dec"       # We still want the default
+    "\n bool l_updateDepth;"
+    "\n vec3 l_opaqueFragPos;",
+    False                    # only do it once i.e. only replace the first match
+)
+mapper.AddShaderReplacement(
+    vtk.vtkShader.Fragment,
+    "//VTK::Base::Init",
+    True,
+    "//VTK::Base::Init\n"
+    "\n l_updateDepth = true;"
+    "\n l_opaqueFragPos = vec3(0.0);",
+    False
+)
+mapper.AddShaderReplacement(
+    vtk.vtkShader.Fragment,
+    "//VTK::Base::Impl",
+    True,
+    "//VTK::Base::Impl"
+    "\n    if(!g_skip && g_srcColor.a > 0.0 && l_updateDepth)"
+    "\n      {"
+    "\n      l_opaqueFragPos = g_dataPos;"
+    "\n      l_updateDepth = false;"
+    "\n      }",
+    False
+)
+mapper.AddShaderReplacement(
+    vtk.vtkShader.Fragment,
+    "//VTK::RenderToImage::Exit",
+    True,
+    "//VTK::RenderToImage::Exit"
+    "\n  if (l_opaqueFragPos == vec3(0.0))"
+    "\n    {"
+    "\n    fragOutput0 = vec4(0.0);"
+    "\n    }"
+    "\n  else"
+    "\n    {"
+    "\n    vec4 depthValue = in_projectionMatrix * in_modelViewMatrix *"
+    "\n                      in_volumeMatrix * in_textureDatasetMatrix *"
+    "\n                      vec4(l_opaqueFragPos, 1.0);"
+    "\n    depthValue /= depthValue.w;"
+    "\n    fragOutput0 = vec4(vec3(0.5 * (gl_DepthRange.far -"
+    "\n                       gl_DepthRange.near) * depthValue.z + 0.5 *"
+    "\n                      (gl_DepthRange.far + gl_DepthRange.near)), 1.0);"
+    "\n    }",
+    False
+)
+
+volume = vtk.vtkVolume()
+volume.SetMapper(mapper)
+volume.SetProperty(volumeProperty)
+
+renWin = vtk.vtkRenderWindow()
+renWin.SetMultiSamples(0)
+renWin.SetSize(301, 300)  # Intentional NPOT size
+
+ren = vtk.vtkRenderer()
+renWin.AddRenderer(ren)
+
+iren = vtk.vtkRenderWindowInteractor()
+iren.SetRenderWindow(renWin)
+
+ren.AddVolume(volume)
+ren.GetActiveCamera().Elevation(-60.0)
+ren.ResetCamera()
+ren.GetActiveCamera().Zoom(1.3)
+
+renWin.Render()
+iren.Start()