[vtkusers] how to render VTK into user provided FBO

[Ken Martin]

Try binding your FBO and context and then use
InitializeFromCurrentContext.  That has some logic to record the current
FBO and use it for subsequent operations.  That might do what you want.

- Ken

On Mon, Dec 3, 2018 at 10:35 PM Max Chen <trlsmax at gmail.com> wrote:

> 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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-- 
Ken Martin PhD
Distinguished Engineer
Kitware Inc.
101 East Weaver Street
Carrboro, North Carolina
27510 USA

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