# Why rendering is slow in GenericRenderWindow if we re-use it
**URL:** https://discourse.vtk.org/t/why-rendering-is-slow-in-genericrenderwindow-if-we-re-use-it/10731
**Category:** Web
**Created:** [February 20, 2023, 10:55am UTC](https://discourse.vtk.org/t/why-rendering-is-slow-in-genericrenderwindow-if-we-re-use-it/10731 "2023-02-20T10:55:41Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@dexter](https://discourse.vtk.org/u/dexter)
#### Post date: [February 20, 2023, 10:55am UTC](https://discourse.vtk.org/t/why-rendering-is-slow-in-genericrenderwindow-if-we-re-use-it/10731/1 "2023-02-20T10:55:41Z")
In my application I did two tests to prouve what I’m saying:
**1 case:**
In each time I want to render a new 3D surface actor, I delete the whole `vtkGenericRenderWindow` and the previous actor / mapper, and I re-create a new ones, doing this the rendering is good but I’m risking to have `Too many open WebGL contexts` warning.
**2 case:**
In each time I want to render a new 3D surface actor, I re-use the same `vtkGenericRenderWindow` and I delete the previous `actor/ mapper` and I create new `actor/ mapper`, doing this the rendering is slow, so when I move the 3D surface with the mouse it is moving so slow.
---
### Author:  [@Forrest](https://discourse.vtk.org/u/Forrest)
#### Post date: [February 20, 2023, 4:07pm UTC](https://discourse.vtk.org/t/why-rendering-is-slow-in-genericrenderwindow-if-we-re-use-it/10731/2 "2023-02-20T16:07:41Z")
The second case shouldn’t necessarily be slow, unless your data is very, very large. You typically never want to do #1.
---
### Author:  [@dexter](https://discourse.vtk.org/u/dexter)
#### Post date: [February 21, 2023, 9:06am UTC](https://discourse.vtk.org/t/why-rendering-is-slow-in-genericrenderwindow-if-we-re-use-it/10731/3 "2023-02-21T09:06:46Z")
Thank you for your answer,
Yes I can say that my data is very large, each polydata (used by the 3D surface actors) size is 30MB and I have 33 patients,
![[video-to-gif output image]](https://discourse.vtk.org/uploads/default/original/2X/9/9cd92558474e30baee8755055fc114c0879c0c3a.gif)
This how I’m doing it in my code:
PS: `context.current[3].GLWindow` is the reference holding my GenericRenderWindow
```auto
const brainRender = async () => {
if (context.current[3]) {
const { actor, mapper, } = context.current[3];
context.current[3].GLWindow.getRenderer().removeAllActors();
if(actor){
actor.delete()
}
if(mapper){
mapper.delete()
}
}
let pd, GLWindow, actor, mapper;
mapper = vtkMapper.newInstance();
actor = vtkActor.newInstance();
GLWindow = context.current[3].GLWindow;
const reader1 = vtkPolyDataReader.newInstance();
await reader1
.setUrl(path)
.then(async () => {
pd = reader1.getOutputData();
})
.catch((error) => {
console.log(error);
});
const originBrain = origin.current;
actor.setMapper(mapper);
actor.setPosition(originBrain[0], originBrain[1], originBrain[2]);
mapper.setInputData(pd);
GLWindow.getRenderer().addActor(actor);
GLWindow.getRenderer().resetCamera();
GLWindow.getRenderer().getActiveCamera().zoom(1.3);
GLWindow.getRenderer().getActiveCamera().pitch(2.3);
GLWindow.getRenderWindow().render();
const obj = {
actor: actor,
mapper: mapper,
GLWindow: GLWindow,
pd: pd,
};
context.current[3] = { ...obj };
};
```
Doing it like this and after displaying 3 or 4 patients, manipulating the 3D surface with the mouse becomes so slow:
![[video-to-gif output image]](https://discourse.vtk.org/uploads/default/original/2X/e/e67d7142abdcb0a34b500aad847730e56eacc81a.gif)
---
### Author:  [@Forrest](https://discourse.vtk.org/u/Forrest)
#### Post date: [February 21, 2023, 3:34pm UTC](https://discourse.vtk.org/t/why-rendering-is-slow-in-genericrenderwindow-if-we-re-use-it/10731/4 "2023-02-21T15:34:43Z")
Can you make a devtools performance profile of the slow 3D surface manipulation? I don’t suppose that you have all 33 polydatas visible in the scene, since it just looks like one. But it shouldn’t be that slow.
---
### Author:  [@dexter](https://discourse.vtk.org/u/dexter)
#### Post date: [February 23, 2023, 8:30am UTC](https://discourse.vtk.org/t/why-rendering-is-slow-in-genericrenderwindow-if-we-re-use-it/10731/5 "2023-02-23T08:30:01Z")
Thank you for your answer, I found the problem,
In each time I’m calling my onClick event I initialize the GLWindow variable with new `vtkGenericRenderWindow`
```auto
let GLWindow = vtkGenericRenderWindow.newInstance();
if (context.current){
GLWindow = context.current[3].GLWindow
}
//...
```
So I just removed the initialisation and it works fine!
```auto
let GLWindow;
if (context.current){
GLWindow = context.current[3].GLWindow
}
//...
```