[vtkusers] Android support for off-screen rendering

[Brian Miller]

However, now I am running into another issue on Android.

I want to read an obj file, render off-screen (in memory, not to an actual window)
and then get a pointer to the vtkImageData.

I was planning to use vtkRenderWindow method SetOffScreenRendering(1);

I got this working in a simple Linux desktop test program.

However, I noticed that this is not officially supported for Android platform.

In VTK-7.0.0/CMake/vtkOpenGL.cmake file, lines 33-35 :

 if (VTK_USE_OFFSCREEN_EGL AND ANDROID)
   message(FATAL_ERROR "You cannot use VTK_USE_OFFSCREEN_EGL on the ANDROID platform")
 endif()

and in vtkEGLRenderWindow.cxx, lines 614-618 :

//----------------------------------------------------------------------------
void vtkEGLRenderWindow::SetOffScreenRendering (int)
{
  // this is determined at compile time: ANDROID -> 0, VTK_USE_OFFSCREEN_EGL -> 1
}

Why is this, and has anyone tried modifying VTK to allow for this.