how to render VTK into user provided FBO

Hi all,

I want VTK render into a FBO I created and use the texture attached to this
FBO to render into a glfw window.

I tried this :
create a class from vtkExternalOpenGLRenderWindow so I can modify the
protected member.

class MyRW : public vtkExternalOpenGLRenderWindow
{
public:
	void SetFBO(unsigned int fbo, unsigned int tex, unsigned int w, unsigned
int h);
};

void MyRW::SetFBO(unsigned int fbo, unsigned int tex, unsigned int w,
unsigned int h)
{

	this->SetBackLeftBuffer(GL_COLOR_ATTACHMENT0);
	this->SetFrontLeftBuffer(GL_COLOR_ATTACHMENT0);
	this->SetBackBuffer(GL_COLOR_ATTACHMENT0);
	this->SetFrontBuffer(GL_COLOR_ATTACHMENT0);

	this->Size[0] = w;
	this->Size[1] = h;
	this->NumberOfFrameBuffers = 1;
	this->DepthRenderBufferObject = 0;
	this->FrameBufferObject = static_cast<unsigned int>(fbo);
	this->TextureObjects[0] = static_cast<unsigned int>(tex);
	this->OffScreenRendering = 1;
	this->OffScreenUseFrameBuffer = 1;
	this->Modified();
}

I also pass the glfw window pointer to vtkCommand::WindowMakeCurrentEvent.

In the glfw loop :

	// render into FBO
	glBindFramebuffer(GL_FRAMEBUFFER, m_fbo);
        myvtk->render();
	glBindFramebuffer(GL_FRAMEBUFFER, 0);

	// use the texture
	glEnable(GL_TEXTURE_2D);
	glBindTexture(GL_TEXTURE_2D, m_tex);
	unsigned int e = glGetError();
	glColor4f(1, 1, 1, 1);
	glBegin(GL_QUADS);
	glTexCoord2f(0.0, 0.0); glVertex3f(-1.0, -1.0, 0);
	glTexCoord2f(1.0, 0.0); glVertex3f(1.0, -1.0, 0);
	glTexCoord2f(1.0, 1.0); glVertex3f(1.0, 1.0, 0);
	glTexCoord2f(0.0, 1.0); glVertex3f(-1.0, 1.0, 0);
	glEnd();
	glBindTexture(GL_TEXTURE_2D, 0);
	glDisable(GL_TEXTURE_2D);

        // draw imgui 
        ImGui_ImplOpenGL2_RenderDrawData(ImGui::GetDrawData());

but it did not work, window is flickering and imgui just disappear.

I setup a cmake test project in github, please help.
https://github.com/trlsmax/imgui-vtk <https://github.com/trlsmax/imgui-vtk>  



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