# Confusion about the use of vtkMapper

**URL:** https://discourse.vtk.org/t/confusion-about-the-use-of-vtkmapper/4640
**Category:** Support
**Created:** [November 12, 2020, 7:21am UTC](https://discourse.vtk.org/t/confusion-about-the-use-of-vtkmapper/4640 "2020-11-12T07:21:32Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![Jone7](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/j/e36b37/32.png) [@Jone7](https://discourse.vtk.org/u/Jone7)
#### Post date: [November 12, 2020, 7:21am UTC](https://discourse.vtk.org/t/confusion-about-the-use-of-vtkmapper/4640/1 "2020-11-12T07:21:32Z")

</div>

I first calculated using vtkTriangleMeshPointNormals Vertex normal, it’s like for the Vertex shader normalMC transmit a value, then I use the vtkPolyDataTangents calculating tangent, when I try to input it, the normal value seems to be covered, what method will be both at the same time the input to the Vertex shader?

Here’s the code I wrote:

```
auto norms = vtkSmartPointer<vtkTriangleMeshPointNormals>::New();
norms->SetInputConnection(triangles->GetOutputPort());
mapper->SetInputConnection(norms->GetOutputPort());

auto tangs = vtkSmartPointer<vtkPolyDataTangents>::New();
tangs->SetInputConnection(triangles->GetOutputPort());
mapper->SetInputConnection(tangs->GetOutputPort());

```

I also noticed that vertex Shader added “Uniform Mat3 normalMatrix”, Can someone help me explain?