OpenGL shader chaining using FrameBuffer woes

gistfile1.txt

// setting up two shaders
bufferPass = setupRenderPass("bufferA.frag", 1 /* toBuffer */)
imagePass = setupRenderPass("image.frag", 0 /* toBuffer */)


// inside setupRenderPass
renderPass setupRenderPass(shaderFile, toBuffer) {
    // ...
    renderPass.prog = getShader(shaderFile);
    renderPass.iChannel0 = glGetUniformLocation(renderPass.prog, "iChannel0");
    if (toFrameBuffer) {
        GLuint FramebufferName = 0;
        glGenFramebuffers(1, &FramebufferName);
        glBindFramebuffer(GL_FRAMEBUFFER, FramebufferName);
        GLuint renderedTexture;
        glActiveTexture(GL_TEXTURE0);
        glGenTextures(1, &renderedTexture);
        glBindTexture(GL_TEXTURE_2D, renderedTexture);
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, winw, winh, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
        glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, renderedTexture, 0);
        GLenum DrawBuffers[1] = {GL_COLOR_ATTACHMENT0};
        glDrawBuffers(1, DrawBuffers); // "1" is the size of DrawBuffers
        if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
            std::cout<<"Error setting up framebuffer!"<<std::endl;
            exit(1);
            return;
        }
        renderPass.FramebufferName = FramebufferName;
        renderPass.texture = renderedTexture;
    }
    return renderPass;

// main loop
display(bufferA);
glBindFramebuffer(GL_FRAMEBUFFER, g_toy.bufferA.FramebufferName);
display(image);
glBindFramebuffer(GL_FRAMEBUFFER, 0);

// display function
void display(renderpass& r) {
    glUseProgram(r.prog);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, r.texture);
    glUniform1i(r.uloc_iChannel, 0);
    glRecti(-1,-1,1,1);
}


// bufferA shader
layout(location = 0) out vec4 color;
...
color = vec4(1, 1, 0, 1);

// image shader
uniform sampler2D iChannel0;
...
color = texture(iChannel0, UV)