How can I use ray cast volume rendering customizing my own shader?

Support
1

Hi,
I’m working on ray cast volume rendering and would like to customize the rendering process by injecting my own shader code using Shader Replacement at specific stages.
So, I tryed to use vtkOpenGLGPUVolumeRayCastMapper to get access to shader control and use AddShaderReplacement(..)

However, when I try to use vtkOpenGLGPUVolumeRayCastMapper, Python reports that the class is not available or hasn’t been imported.
How can I access or enable this class in my environment?

Thanks in advance for your help.

2

In python you may have to explicitly import like this:

from vtkmodules.vtkRenderingVolumeOpenGL2 import vtkOpenGLGPUVolumeRayCastMapper

Also I think AddShaderReplacement(..) has to be called on the volumeprops and not the mapper itself.

3

Yes, I’m doing exactly what you described. Here’s a snippet of my code:

Build the volume data from a set of images

vtk_image = numpy_to_vtk_image_data(np_array, spacing, origin)

mapper = vtkOpenGLGPUVolumeRayCastMapper()
mapper.SetInputData(vtk_image)
mapper.SetBlendModeToComposite()
volumeProperty = vtk.vtkVolumeProperty()

define the specific volume properties: SetScalarOpacity & color

#…
volume = vtk.vtkVolume()
volume.SetMapper(mapper) # vtkOpenGLGPUVolumeRayCastMapper
volume.SetProperty(volumeProperty)

shaderProp = volume.GetShaderProperty()

just for debugging, all the fragments are set to red color

shaderProp.AddShaderReplacement(
vtk.vtkShader.Fragment,
“//VTK::Base::Color::Impl”,
True,
“g_fragColor = vec4(1.0, 0.0, 0.0, 1.0);”,
False
)

renderer = vtk.vtkRenderer()
renderer.AddVolume(volume)

continue specifying a RenderWindow etc.

Since the render shows the expected volume output instead of the red image, it seems the shader replacement isn’t taking effect.

Thanks in advance for your help,

4

Try //VTK::Shading::Impl. For a list of fragment shader replacements for this mapper, see Rendering/VolumeOpenGL2/shaders/raycasterfs.glsl.