Coordinate System issue when using Scoped FrameBuffer

Hi everyone!

I’ve been having issues with using Scoped Frame Buffers in Cinder, and I’m not sure where it is coming from. When I do not use a frame-buffer, I am trying to get a black circle to draw to the center of the screen with a radius of 200. I am able to do this without frame buffers, so I know that part of my code is correct.

However, when I try to use FBOs, this is what happens:

. The coordinate system shifts and becomes scaled up, which is really weird because I set the camera to be pointing at 0,0.

I’m running this on a Macbook Pro 2015 with Retina display (so I’m not sure if it’s a mac issue or not!) I copied my .cpp file below but I put my full code on github so that it’s easier to download and replicate and see whether it’s a computer issue or code issue:

class CinderForumTestApp : public App { 
        const int FBO_W = 600;
        const int FBO_H = 600;
        int width = cinder::app::getWindowWidth();
        int height = cinder::app::getWindowHeight();    
        vector<vec2> offsetArray;   
        int offsetSize = 5;
        gl::FboRef mScene;
        gl::FboRef mHDRComp;
        gl::TextureRef mTexture;
        gl::GlslProgRef mCompShader;
        CameraPersp mCam;

    void setup() override;
    void update() override;
    void draw() override;
    void prepareSettings(Settings *settings);

void CinderForumTestApp::setup()
    // this is to initialize positions to sample from the texture
    // to create a layered smoky effect in the background
    for (int i = 0; i < offsetSize; i++){
        offsetArray.push_back(vec2(randFloat(-0.05, 0.05), randFloat(-0.05, 0.05)));

    //Frame Buffer Stuff - creating composite frame buffer
    mHDRComp = gl::Fbo::create(FBO_W, FBO_H);
    //creating base frame buffer
    mScene = gl::Fbo::create(toPixels(getWindowWidth()),toPixels(getWindowHeight()));
    //background texture
    mTexture = gl::Texture::create(loadImage(loadAsset("smoke2.jpg")));
    //setting up camera
    vec3 camPos = glm::vec3(0,0,800);
    mTexture -> setWrap(GL_REPEAT, GL_REPEAT);
    mCam.lookAt(camPos, glm::vec3(0.0f), glm::vec3(0,1,0));
    mCam.setPerspective(75, getWindowAspectRatio(), 01.01f, 2500.0f);
    mCompShader = gl::GlslProg::create(loadAsset("comp.vert"), loadAsset("comp.frag"));

void CinderForumTestApp::update()

void CinderForumTestApp::draw()
    gl::clear( Color( 0, 0, 0 ) );

//Base Frame Buffer
    //scoping it to frame buffer. It draws fine without the scoping
    // but once you uncomment it, the scene seems to get stretched out
    // and translate. This is the main problem area
    gl::ScopedFramebuffer scpScene(mScene);
    gl::ScopedMatrices scpCam;
    //clear with white to see whether it draws
    gl::clear( Color( 1, 1, 1 ) );
    gl::ScopedGlslProg scpGL(gl::getStockShader(gl::ShaderDef().texture().lambert().color()));
    //drawing sphere at 0,0 (which should be at the center of the screen)

// composite buffer, layering the images on top
// commenting this out because there seems to be something wrong with the
// mScene buffer itself, but not this one
    gl::ScopedFramebuffer scpScene(mHDRComp);
    gl::ScopedGlslProg scpCom(mCompShader);
    gl::ScopedTextureBind scpSceneTex(mScene->getColorTexture(),0);
    gl::ScopedTextureBind scpComposite(mTexture,1);
    vec2 arr [offsetSize];
    for(int i = 0; i < offsetSize; i++){
        arr[i] = offsetArray[i];
    //passing array of initial starts to shader
    mCompShader->uniform("offsetArray", arr, offsetSize);
//drawing frame buffer to screen
    gl::ScopedMatrices scpa;
    gl::ScopedDepth scpD(false);
    // scoped Viewport is also acting very strange when the mScene
    // scoping is uncommented. I'm not sure how it's translating stuff
  //gl::ScopedViewport scpVP(ivec2(0), ivec2(toPixels(getWindowWidth()), toPixels(getWindowHeight())));`
    gl::ScopedTextureBind scpScene(mScene-> getColorTexture(),0);
    gl::ScopedGlslProg scpGL(gl::getStockShader(gl::ShaderDef().texture()));
//trying to print out mScene to see if there is something wrong
// with the mScene buffer or something else
// seems to be something wrong with the Frame Buffer itself
if(getElapsedFrames() < 5){
    string filepath = "<add your filepath>";
    writeImage( filepath+ "testMScene.tif", mScene->readPixels8u(mScene->getBounds()));
CINDER_APP( CinderForumTestApp, RendererGl, [&](App::Settings *settings){
    settings->setWindowSize(600, 600);

Thank you!


you need to adjust the viewport as well. After binding the Fbo, you can easily do this with a call to:

gl::ScopedViewport scpViewport( mScene->getSize() );


1 Like

That fixed it! Thank you so much! I was wondering why I had to bind the viewport in the mScene frame buffer area? My understanding was that if it wasn’t specified, it would draw to the same coordinate system as if I wasn’t scoping anything