# Why vtkGenericRenderWindow keeps creating 2 canvas?

**URL:** https://discourse.vtk.org/t/why-vtkgenericrenderwindow-keeps-creating-2-canvas/10937
**Category:** Web
**Created:** [March 10, 2023, 12:45pm UTC](https://discourse.vtk.org/t/why-vtkgenericrenderwindow-keeps-creating-2-canvas/10937 "2023-03-10T12:45:34Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![stoune](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/s/eb8c5e/32.png) [@stoune](https://discourse.vtk.org/u/stoune)
#### Post date: [March 10, 2023, 12:45pm UTC](https://discourse.vtk.org/t/why-vtkgenericrenderwindow-keeps-creating-2-canvas/10937/1 "2023-03-10T12:45:34Z")

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I was working normally with vtk.js but today when I created a new project, I don’t know why when I render my renderwindow, it creates two canvas like in the code sandbox below

> **[busy-mountain-bg19kb - CodeSandbox](https://codesandbox.io/s/busy-mountain-bg19kb?file=%2Fsrc%2FApp.js)**
>
> busy-mountain-bg19kb by stounej using @emotion/react, @emotion/styled, @kitware/vtk.js, @mui/material, loader-utils, react, react-dom, react-scripts

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### Author: ![Sebastien\_Jourdain](https://discourse.vtk.org/user_avatar/discourse.vtk.org/sebastien_jourdain/32/100_2.png) [@Sebastien\_Jourdain](https://discourse.vtk.org/u/Sebastien_Jourdain)
#### Post date: [March 10, 2023, 3:11pm UTC](https://discourse.vtk.org/t/why-vtkgenericrenderwindow-keeps-creating-2-canvas/10937/2 "2023-03-10T15:11:50Z")

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`brainRender` get called twice… Just a react thing not vtk.js related.