# Rendering artifact

**URL:** https://discourse.vtk.org/t/rendering-artifact/8830
**Category:** Support
**Created:** [June 29, 2022, 2:58pm UTC](https://discourse.vtk.org/t/rendering-artifact/8830 "2022-06-29T14:58:28Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![rprueckl](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/r/c37758/32.png) [@rprueckl](https://discourse.vtk.org/u/rprueckl)
#### Post date: [June 29, 2022, 2:58pm UTC](https://discourse.vtk.org/t/rendering-artifact/8830/1 "2022-06-29T14:58:28Z")

</div>

Dear all,

I am writing extensions for 3D Slicer and encountered some rendering artifacts:

I manually load an obj and a texture and want to display this. The result is as follows:  
 ![image](https://discourse.vtk.org/uploads/default/original/2X/4/4e840462c08cf0f97ff9e490ea55d616f165f591.png)

When I use the same code, but add the actor to one of the standard slicer 3d views, the result looks like this (as expected):

 ![image](https://discourse.vtk.org/uploads/default/original/2X/8/8c4c65061bb428d54ae237d57a0b07af4aed66dd.png)

I found a workaround to remove the artifact: The object in question basically only has two colors. I initially created the texture mapping such that triangles of the same color would map to the same texture coordinates. This means that texture coordinates of the same-color triangles overlapped. This is when I saw the artifact.

I changed mapping such that each triangle now has its own space on the texture (i.e. no overlap anymore), and the artifact was gone.

I have no idea about the root-cause for this. Maybe someone of you does.

This was done with VTK version v7.0.0.rc1-9087-g31dc6a08b8.  
The display pipeline is as follows:

```auto
// input:
vtkSmartPointer<vtkPolyData> geometry; // read from hdd with vtkOBJReader
vtkSmartPointer<vtkImageData> texture; // read from hdd with vtkPNGReader

// prepare geometry
vtkNew<vtkPolyDataMapper> polyDataMapper;
polyDataMapper->SetInputData(geometry);

// prepare texture
int extent[6];
texture->GetExtent(extent);

vtkNew<vtkImageCanvasSource2D> selectionOverlay;
selectionOverlay->SetScalarTypeToUnsignedChar();
selectionOverlay->SetExtent(extent);
selectionOverlay->SetNumberOfScalarComponents(3);
selectionOverlay->SetDrawColor(1.0, 0.0, 0.0);
selectionOverlay->FillBox(extent[0], extent[1], extent[2], extent[3]);
selectionOverlay->Update();

textureBlender = vtkSmartPointer<vtkImageBlend>::New();
textureBlender->AddInputData(texture);
textureBlender->AddInputData(selectionOverlay->GetOutput());
textureBlender->SetOpacity(0, 1.0);
textureBlender->SetOpacity(1, 0.0);

vtkNew<vtkTexture> textureObject;
textureObject->SetInputConnection(textureBlender->GetOutputPort());
textureObject->Update();

// prepare actor
actor = vtkSmartPointer<vtkActor>::New();
actor->SetMapper(polyDataMapper);
actor->SetTexture(textureObject);
renderer->AddActor(actor);

```