[vtkusers] Strange rendering with 2-voxel thick volume

[Aashish Chaudhary]

Please make sure that your sampling distance is less than < 2. You can set
the sampling distance manually in the API.

On Wed, Oct 4, 2017 at 8:23 AM Elvis Stansvik <elvis.stansvik at orexplore.com>
wrote:

> Hi all,
>
> In the test case below, I render one 200x200x2 volume and one
> 200x200x3 volume, both with the same settings.
>
> The 200x200x3 volume looks as expected (the light gray one in the
> attached screenshot), while the 200x200x2 one looks strange (too dark,
> and with some kind of gradient artifact).
>
> Is there some limitation on rendering a volume that is only 2 thick in
> one of the dimensions? I can understand why a volume of thickness 1
> can't be rendered properly, since VTK must have values to interpolate
> between, but 2 should be OK right?
>
> Thanks for any help.
>
> Elvis
>
>
> main.cpp:
>
> #include <algorithm>
>
> #include <vtkColorTransferFunction.h>
> #include <vtkGenericOpenGLRenderWindow.h>
> #include <vtkGPUVolumeRayCastMapper.h>
> #include <vtkImageData.h>
> #include <vtkNew.h>
> #include <vtkPiecewiseFunction.h>
> #include <vtkProperty.h>
> #include <vtkRenderer.h>
> #include <vtkRenderWindow.h>
> #include <vtkRenderWindowInteractor.h>
> #include <vtkVolume.h>
> #include <vtkVolumeProperty.h>
>
> int main(int argc, char *argv[])
> {
>     vtkNew<vtkColorTransferFunction> colorFunction;
>     colorFunction->AddRGBPoint(0.0, 0.0, 0.0, 0.0);
>     colorFunction->AddRGBPoint(1.0, 0.0, 0.0, 0.0);
>
>     vtkNew<vtkPiecewiseFunction> opacityFunction;
>     opacityFunction->AddPoint(0.0, 0.0);
>     opacityFunction->AddPoint(1.0, 1.0);
>
>     // A 200x200x2 volume
>     vtkNew<vtkImageData> imageData;
>     imageData->SetExtent(0, 199, 0, 199, 0, 1);
>     imageData->AllocateScalars(VTK_FLOAT, 1);
>     std::fill_n(static_cast<float *>(imageData->GetScalarPointer()),
> 200 * 200 * 2, 0.01);
>
>     vtkNew<vtkGPUVolumeRayCastMapper> volumeMapper;
>     volumeMapper->SetInputData(imageData.Get());
>
>     vtkNew<vtkVolumeProperty> volumeProperty;
>     volumeProperty->SetScalarOpacity(opacityFunction.Get());
>     volumeProperty->SetColor(colorFunction.Get());
>     volumeProperty->ShadeOff();
>
>     vtkNew<vtkVolume> volume;
>     volume->SetMapper(volumeMapper.Get());
>     volume->SetProperty(volumeProperty.Get());
>     volume->SetPosition(120, 0, 0);
>
>     // A 200x200x3 volume
>     vtkNew<vtkImageData> imageData2;
>     imageData2->SetExtent(0, 199, 0, 199, 0, 2);
>     imageData2->AllocateScalars(VTK_FLOAT, 1);
>     std::fill_n(static_cast<float *>(imageData2->GetScalarPointer()),
> 200 * 200 * 3, 0.01);
>
>     vtkNew<vtkGPUVolumeRayCastMapper> volumeMapper2;
>     volumeMapper2->SetInputData(imageData2.Get());
>
>     vtkNew<vtkVolumeProperty> volumeProperty2;
>     volumeProperty2->SetScalarOpacity(opacityFunction.Get());
>     volumeProperty2->SetColor(colorFunction.Get());
>     volumeProperty2->ShadeOff();
>
>     vtkNew<vtkVolume> volume2;
>     volume2->SetMapper(volumeMapper2.Get());
>     volume2->SetProperty(volumeProperty2.Get());
>     volume2->SetPosition(-120, 0, 0);
>
>     vtkNew<vtkRenderer> renderer;
>     renderer->AddVolume(volume.Get());
>     renderer->AddVolume(volume2.Get());
>     renderer->SetBackground(1.0, 1.0, 1.0);
>
>     // Render with "plain" render window / interactor
>     vtkNew<vtkRenderWindow> window;
>     window->SetMultiSamples(0);
>     window->AddRenderer(renderer.Get());
>
>     vtkNew<vtkRenderWindowInteractor> interactor;
>     interactor->SetRenderWindow(window.Get());
>     interactor->Start();
>
>     return 0;
> }
>
>
> CMakeLists.txt:
>
> cmake_minimum_required(VERSION 3.1)
>
> project(TestCase)
>
> find_package(VTK 8.0 COMPONENTS
>     vtkCommonCore
>     vtkCommonDataModel
>     vtkCommonExecutionModel
>     vtkCommonMath
>     vtkFiltersSources
>     vtkGUISupportQt
>     vtkInteractionStyle
>     vtkRenderingCore
>     vtkRenderingOpenGL2
>     vtkRenderingVolume
>     vtkRenderingVolumeOpenGL2
>     REQUIRED
> )
>
> add_executable(TestCase main.cpp)
>
> target_link_libraries(TestCase PUBLIC
>     vtkCommonCore
>     vtkCommonDataModel
>     vtkCommonExecutionModel
>     vtkCommonMath
>     vtkFiltersSources
>     vtkInteractionStyle
>     vtkRenderingCore
>     vtkRenderingOpenGL2
>     vtkRenderingVolume
>     vtkRenderingVolumeOpenGL2
> )
>
> target_include_directories(TestCase PUBLIC
>     ${VTK_INCLUDE_DIRS}
> )
>
> target_compile_definitions(TestCase PUBLIC
>     ${VTK_DEFINITIONS}
> )
>
> set_target_properties(TestCase PROPERTIES
>     CXX_STANDARD 14
>     CXX_STANDARD_REQUIRED ON
> )
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