OpenGL multiple Framebuffer chaining and post processing - opengl

Question

I have three different framebuffer objects for three different steps:
GLuint fbo1; // Step1: draw initial scene
GLuint fbo2; // Step2: apply lens effect shader
GLuint fbo3; // Step3: final smoothing
I want to draw my initial scene as a texture attached to fbo1.
Then apply a lens-shader on that and save it as a texture in fbo2.
Then apply a smoothing-shader on fbo2 and save it to fbo3.
The code in my main render function, uses a few helper functions, and is as follows:
// Step1
useFrameBuffer(fbo1, fbo1); // src , dest
DrawInitialScene();
// Step2
LensShader.use(); // a glsl shader program class
useFrameBuffer(fbo1, fbo2); // src , dest
drawQuadOnFbo(fbo2Texture);
// Step3
SmoothingShader.use(); // a glsl shader program class
useFrameBuffer(fbo2, fbo3); // src , dest
drawQuadOnFbo(fbo3Texture);
// Final Copy Step to OpenGL default FBO
int width = self.frame.size.width;
int height = self.frame.size.height;
glBindFramebuffer(GL_READ_FRAMEBUFFER, fbo3);
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0); //destination
glBlitFramebuffer(0, 0, width, height, 0, 0, width, height, GL_COLOR_BUFFER_BIT, GL_LINEAR);
The helper function useFrameBuffer(src, dest), simply sets the source framebuffer to read from and destination write framebuffer:
void useFrameBuffer (GLuint fboSrc , GLuint fboDest)
{
glBindFramebuffer(GL_READ_FRAMEBUFFER, fboSrc);
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fboDest);
GLenum drawbufs[] = {GL_COLOR_ATTACHMENT0};
glDrawBuffers(1, drawbufs);
glReadBuffer(GL_COLOR_ATTACHMENT0);
glViewport(0, 0, width, height); // width, height are private to class
}
To apply the shader on the output of fbo1 and fbo2, I am drawing a quad with a texture associated to the respective frame-buffers:
void drawQuadOnFbo(GLuint fboTexture) {
glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // We're not using stencil buffer now
glBlendFunc(GL_ONE, GL_ONE);
glBindVertexArray(quadVAO);
glDisable(GL_DEPTH_TEST);
glBindTexture(GL_TEXTURE_2D, fboTexture);
glDrawArrays(GL_TRIANGLES, 0, 6);
glBindVertexArray(0);
}
The Problem:
The problem is that output appears to be a combination of Step1 and Step3 only. Looks like the Step2 is completely missed out. You can see in the final copy step, I am copying the contents of fbo3 to the final OpenGL default fbo using:
glBindFramebuffer(GL_READ_FRAMEBUFFER, fbo3);
If I change this to fbo2, then I do see the results of applying Step2 (but then I don't have Step3).
So it looks like that both fbo2 and fbo3 are connected directly to the output of fbo1, but not connected to each other.
How can I fix that ??
Other Helper Functions:
I initialised my Framebuffers at the start of the application, outside the main render function using the method below:
GLuint initFrameBuffer( int width, int height, GLenum textureTarget) {
// 1. Create FBO
GLuint fbo;
glGenFramebuffers(1, &fbo);
// 2. Bind it
glBindFramebuffer(GL_FRAMEBUFFER, fbo);
// FrameBuffer Requirements
// (i). atleast 1 buffer (color, depth, stencil)
// (ii). atleast 1 color-attachment
// (iii). all attachments should be complete
// (iv). same no. of samples for each buffer
// 3. Texture Attachment
GLuint quadTex; // texture to be associated to this FBO
glActiveTexture(textureTarget);
glGenTextures(1, &quadTex);
glBindTexture(GL_TEXTURE_2D, quadTex);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
// attach it as COLOR-ATTACHMENT 0
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, quadTex, 0);
// 4. RenderBuffer attachement
GLuint rbo;
glGenRenderbuffers(1, &rbo);
glBindRenderbuffer(GL_RENDERBUFFER, rbo);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH24_STENCIL8, width, height);
glBindRenderbuffer(GL_RENDERBUFFER, 0);
// attach it
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, rbo);
// 5. Set Targets for fragment shader output
GLenum drawbufs[] = {GL_COLOR_ATTACHMENT0};
glDrawBuffers(1, drawbufs);
// 6. Check that the FrameBuffer is complete
if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE){
NSLog(#"ERROR::FRAMEBUFFER:: Framebuffer is not complete!");
return fboObj;
}
// 7. revert to Default
glBindFramebuffer(GL_FRAMEBUFFER, 0);
return fbo;
}