[vtkusers] Artifacts along bounding box edges in volume rendering

[Róbert Špir]

Hi Elvis,
this is caused by multisampling, if you set window->SetMultiSamples(0); the
artifact will disappear. I can reproduce it in your example on windows with
nvidia card.

If you need antialiasing, you can try using FXAA which doesn't produce these
artifacts
#include <vtkFXAAOptions.h>

	vtkSmartPointer<vtkFXAAOptions> FXAAOptions =
vtkSmartPointer<vtkFXAAOptions>::New();	
	FXAAOptions->SetRelativeContrastThreshold(0.125);
	FXAAOptions->SetHardContrastThreshold(0.045);
	FXAAOptions->SetSubpixelBlendLimit(0.75);
	FXAAOptions->SetSubpixelContrastThreshold(0.25);
	FXAAOptions->SetUseHighQualityEndpoints(true);
	FXAAOptions->SetEndpointSearchIterations(12);

	renderer->SetFXAAOptions(FXAAOptions);
	renderer->SetUseFXAA(true);

Robert

-----Original Message-----
From: vtkusers [mailto:vtkusers-bounces at vtk.org] On Behalf Of Elvis Stansvik
Sent: Monday, March 13, 2017 7:53 AM
To: VTK Users <vtkusers at vtk.org>
Subject: Re: [vtkusers] Artifacts along bounding box edges in volume
rendering

2017-03-10 10:11 GMT+01:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
> 2017-03-10 10:07 GMT+01:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
>> Hi all,
>>
>> I'm trying to debug a problem with artifacts appearing around the 
>> bounding box edges in my volume rendering (at certain camera angles).
>> I can reproduce the problem with the minimal test case below. In the 
>> attached screen shot, notice the faint white artifacts along the 
>> bounding box edges.
>>
>> Anyone know where these come from and how I can fix it?
>
> I forgot to say, this is with VTK 7.1.0.

Noone who knows where this comes from? Would be great if someone could
confirm that they can reproduce it with my test case, as I'm beginning to
suspect it might be graphics card specific (I'm on Linux, Intel graphics).

Should I post to vtk-dev perhaps?

Elvis

>
> Elvis
>
>>
>> Thanks in advance,
>> Elvis
>>
>>
>> main.cpp:
>>
>> #include <algorithm>
>>
>> #include <vtkCamera.h>
>> #include <vtkColorTransferFunction.h> #include 
>> <vtkGPUVolumeRayCastMapper.h> #include <vtkImageData.h> #include 
>> <vtkNew.h> #include <vtkPiecewiseFunction.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);
>>
>>     vtkNew<vtkImageData> data;
>>     data->SetExtent(0, 200, 0, 200, 0, 200);
>>     data->AllocateScalars(VTK_FLOAT, 1);
>>     std::fill_n(static_cast<float *>(data->GetScalarPointer()), 
>> 8000000, 0.1);
>>
>>     vtkNew<vtkGPUVolumeRayCastMapper> mapper;
>>     mapper->SetInputData(data.Get());
>>
>>     vtkNew<vtkVolumeProperty> property;
>>     property->SetScalarOpacity(opacityFunction.Get());
>>     property->SetColor(colorFunction.Get());
>>
>>     vtkNew<vtkVolume> volume;
>>     volume->SetMapper(mapper.Get());
>>     volume->SetProperty(property.Get());
>>
>>     vtkNew<vtkRenderer> renderer;
>>     renderer->AddVolume(volume.Get());
>>     renderer->SetBackground(1.0, 1.0, 1.0);
>>
>>     vtkNew<vtkRenderWindow> window;
>>     window->AddRenderer(renderer.Get());
>>
>>     // Position camera such that artifacts appear
>>     auto camera = renderer->GetActiveCamera();
>>     camera->SetPosition(500.0, 220.0, 500.0);
>>     camera->SetFocalPoint(0.0, 80.0, 0.0);
>>     renderer->ResetCameraClippingRange();
>>
>>     vtkNew<vtkRenderWindowInteractor> interactor;
>>     interactor->SetRenderWindow(window.Get());
>>     interactor->Start();
>>
>>     return 0;
>> }
>>
>>
>> CMakeLists.txt:
>>
>> cmake_minimum_required(VERSION 3.1)
>>
>> project(TestCase)
>>
>> set(CMAKE_PREFIX_PATH ${CMAKE_PREFIX_PATH} /opt/VTK7)
>>
>> find_package(VTK 7.1 COMPONENTS
>>     vtkCommonCore
>>     vtkCommonDataModel
>>     vtkCommonExecutionModel
>>     vtkCommonMath
>>     vtkInteractionStyle
>>     vtkRenderingCore
>>     vtkRenderingOpenGL2
>>     vtkRenderingVolume
>>     vtkRenderingVolumeOpenGL2
>>     REQUIRED
>> )
>>
>> add_executable(TestCase WIN32 main.cpp)
>>
>> target_link_libraries(TestCase PUBLIC
>>     vtkCommonCore
>>     vtkCommonDataModel
>>     vtkCommonExecutionModel
>>     vtkCommonMath
>>     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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