[vtkusers] how to render VTK into user provided FBO

[Max Chen]

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 via vtkusers]

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

Post by Max Chen
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.
create a class from vtkExternalOpenGLRenderWindow so I can modify the
protected member.
class MyRW : public vtkExternalOpenGLRenderWindow
{
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.
// 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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Distinguished Engineer
Kitware Inc.
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Carrboro, North Carolina
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[Max Chen]

Thank you. Now I have a working prototype.
But I get a strangle issue, I can only resize the offscreen
vtkGenericOpenGLRenderWindow 3 times, otherwise I get error like :
ERROR: In E:\projects\VTK-8.1.2\Rendering\OpenGL2\vtkOpenGLActor.cxx, line
107
vtkOpenGLActor (0B2C4C10): failed after Render 1 OpenGL errors detected
0:(1285)out of memory

the resize code is :
void MyVTKRenderer::UpdateSize(unsigned int w, unsigned int h)
{
if (w == m_Width && h == m_Height)
return;

if (w == 0 || h == 0)
return;

m_Width = w;
m_Height = h;

// resize the render window
m_vtkRenderWindow->SetSize(m_Width, m_Height);
m_vtkRenderWindow->FullScreenOn();
m_vtkRenderWindow->OffScreenRenderingOn();
//m_vtkRenderWindow->SetMultiSamples(0);
m_vtkRenderWindow->Modified();
m_vtkRenderWindowInteractor->UpdateSize(m_Width, m_Height);
m_vtkRenderWindowInteractor->Modified();
m_IsInited = false;

// delete old fbo
glDeleteBuffers(1, &m_fbo);
glDeleteBuffers(1, &m_rbo);
glDeleteTextures(1, &m_tex);

// create a texture object
glGenTextures(1, &m_tex);
glBindTexture(GL_TEXTURE_2D, m_tex);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, m_Width, m_Height, 0, GL_RGB,
GL_UNSIGNED_BYTE, 0);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glBindTexture(GL_TEXTURE_2D, 0);
// create a renderbuffer object to store depth info
glGenRenderbuffers(1, &m_rbo);
glBindRenderbuffer(GL_RENDERBUFFER, m_rbo);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, m_Width,
m_Height);
glBindRenderbuffer(GL_RENDERBUFFER, 0);

// create a framebuffer object
glGenFramebuffers(1, &m_fbo);
glBindFramebuffer(GL_FRAMEBUFFER, m_fbo);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D,
m_tex, 0);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT,
GL_RENDERBUFFER, m_rbo);
glBindFramebuffer(GL_FRAMEBUFFER, 0);
}

Another issue is , these code can't work on VTK-8.2 rc1



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[Max Chen]

Everything works now. Code is update to github repo.

I have to remove the actor before resize the vtkGenericOpenGLRenderWindow
and add it back.



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