# MultiVolume Rendering with VTKOpenglGPURaycastiongmapper : rendering failed problem

**URL:** https://discourse.vtk.org/t/multivolume-rendering-with-vtkopenglgpuraycastiongmapper-rendering-failed-problem/12776
**Category:** Support
**Created:** [November 22, 2023, 2:07pm UTC](https://discourse.vtk.org/t/multivolume-rendering-with-vtkopenglgpuraycastiongmapper-rendering-failed-problem/12776 "2023-11-22T14:07:29Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![JamesHOE](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/j/ce73a5/32.png) [@JamesHOE](https://discourse.vtk.org/u/JamesHOE)
#### Post date: [November 22, 2023, 2:07pm UTC](https://discourse.vtk.org/t/multivolume-rendering-with-vtkopenglgpuraycastiongmapper-rendering-failed-problem/12776/1 "2023-11-22T14:07:29Z")

</div>

I’m trying to use vtkMultivolume with vtkOpenglGPUVolumeRayCastMapper in VTK 9.3 in C++

When the blending mode of vtkOpenglGPUVolumeRayCastMapper is set to SetBlendModeToIsoSurface it works very well but the rendering details are very rough, as shown in Figure 1

 ![20231122.PNG](https://discourse.vtk.org/uploads/default/original/2X/4/451f03e6e6ae5eead6bd7a49871b1f4ff4d5976c.jpeg)

Because when **using vtkvolume with vtkOpenglGPUVolumeRayCastMapper** and setting the blending mode **at SetBlendModeToMaximumIntensity,** I can get very good rendering details, as shown in Figure 2

 ![20231122_1](https://discourse.vtk.org/uploads/default/original/2X/1/18d829fac9dfda7e977b2c2c3b418ccd9a024810.png)

So I tried to set the blending mode of **vtkOpenglGPUVolumeRayCastMapper to SetBlendModeToMaximumIntensity** in **vtkMultivolume case** to get better rendering details, but the rendering is failed. The following is the error code

 ![20231122_2](https://discourse.vtk.org/uploads/default/original/2X/d/d631d9c3a578d2653587ea9d8b2af36abe98402b.png)

Did I do something wrong?

Please give me some suggestions.  
Thanks