I am using render to texture concept with glFramebufferTexture1D. I am drawing a cube on non-default FBO with all the vertices as -1,1 (maximum) in X Y Z direction. Now i am setting viewport to X while rendering on non default FBO. My background is blue with white color of cube.

For default FBO, i have created 1-D texture and attached this texture to above FBO with color attachment. I am setting width of texture equal to width*height of above FBO view-port. Now, when i render this texture to on another cube, i can see continuous white color on start or end of each face of the cube. That means part of the face is white and rest is blue. I am not sure whether this behavior is correct or not. I expect all the texels should be white as i am using -1 and 1 coordinates for cube rendered on non-default FBO.

code:

#define WIDTH 3
#define HEIGHT 3

GLfloat vertices8[]={
        1.0f,1.0f,1.0f,
        -1.0f,1.0f,1.0f,
        -1.0f,-1.0f,1.0f,
        1.0f,-1.0f,1.0f,//face 1

        1.0f,-1.0f,-1.0f,
        -1.0f,-1.0f,-1.0f,
        -1.0f,1.0f,-1.0f,
        1.0f,1.0f,-1.0f,//face 2

        1.0f,1.0f,1.0f,
        1.0f,-1.0f,1.0f,
        1.0f,-1.0f,-1.0f,
        1.0f,1.0f,-1.0f,//face 3                

        -1.0f,1.0f,1.0f,
        -1.0f,1.0f,-1.0f,
        -1.0f,-1.0f,-1.0f,
        -1.0f,-1.0f,1.0f,//face 4

        1.0f,1.0f,1.0f,
        1.0f,1.0f,-1.0f,
        -1.0f,1.0f,-1.0f,
        -1.0f,1.0f,1.0f,//face 5

        -1.0f,-1.0f,1.0f,
        -1.0f,-1.0f,-1.0f,
        1.0f,-1.0f,-1.0f,
        1.0f,-1.0f,1.0f//face 6     


};
GLfloat vertices[]=
    {
        0.5f,0.5f,0.5f,
        -0.5f,0.5f,0.5f,
        -0.5f,-0.5f,0.5f,
        0.5f,-0.5f,0.5f,//face 1

        0.5f,-0.5f,-0.5f,
        -0.5f,-0.5f,-0.5f,
        -0.5f,0.5f,-0.5f,
        0.5f,0.5f,-0.5f,//face 2

        0.5f,0.5f,0.5f,
        0.5f,-0.5f,0.5f,
        0.5f,-0.5f,-0.5f,
        0.5f,0.5f,-0.5f,//face 3                

        -0.5f,0.5f,0.5f,
        -0.5f,0.5f,-0.5f,
        -0.5f,-0.5f,-0.5f,
        -0.5f,-0.5f,0.5f,//face 4

        0.5f,0.5f,0.5f,
        0.5f,0.5f,-0.5f,
        -0.5f,0.5f,-0.5f,
        -0.5f,0.5f,0.5f,//face 5

        -0.5f,-0.5f,0.5f,
        -0.5f,-0.5f,-0.5f,
        0.5f,-0.5f,-0.5f,
        0.5f,-0.5f,0.5f//face 6     

    };

    GLuint indices[] =
      {
         0, 2, 1,
         0, 3, 2, 
         4, 5, 6,
         4, 6, 7,
         8, 9, 10,
         8, 10, 11, 
         12, 15, 14,
         12, 14, 13, 
         16, 17, 18,
         16, 18, 19, 
         20, 23, 22,
         20, 22, 21
      };



GLfloat texcoord[] = 
{
        0.0, 0.0,
        1.0, 0.0,
        1.0, 1.0,
        0.0, 1.0,

        0.0, 0.0,
        1.0, 0.0,
        1.0, 1.0,
        0.0, 1.0,

        0.0, 0.0,
        1.0, 0.0,
        1.0, 1.0,
        0.0, 1.0,

        0.0, 0.0,
        1.0, 0.0,
        1.0, 1.0,
        0.0, 1.0,

        0.0, 0.0,
        1.0, 0.0,
        1.0, 1.0,
        0.0, 1.0,

        0.0, 0.0,
        1.0, 0.0,
        1.0, 1.0,
        0.0, 1.0
};

glGenTextures(1, &id1);
glBindTexture(GL_TEXTURE_1D, id1);

glGenFramebuffers(1, &Fboid);

glTexParameterf(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameterf(GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

glTexParameterf(GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);

glTexImage1D(GL_TEXTURE_1D, 0, GL_RGBA,  WIDTH*HEIGHT , 0, GL_RGBA, GL_UNSIGNED_BYTE,0);

glBindFramebuffer(GL_FRAMEBUFFER, Fboid);

glFramebufferTexture1D(GL_DRAW_FRAMEBUFFER,GL_COLOR_ATTACHMENT0,GL_TEXTURE_1D,id1,0);


draw_cube();

glBindFramebuffer(GL_FRAMEBUFFER, 0);

draw();

}
draw_cube()
{
    glViewport(0, 0, WIDTH, HEIGHT);
    glClearColor(0.0f, 0.0f, 0.5f, 1.0f);


    glClear(GL_COLOR_BUFFER_BIT);

    glEnableVertexAttribArray(glGetAttribLocation(temp.psId,"position"));

    glVertexAttribPointer(glGetAttribLocation(temp.psId,"position"), 3, GL_FLOAT, GL_FALSE, 0,vertices8);

    glDrawArrays (GL_TRIANGLE_FAN, 0, 24);

}

draw()
{
    glClearColor(1.0f, 0.0f, 0.0f, 1.0f);


    glClearDepth(1.0f);


    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glEnableVertexAttribArray(glGetAttribLocation(shader_data.psId,"tk_position"));

    glVertexAttribPointer(glGetAttribLocation(shader_data.psId,"tk_position"), 3, GL_FLOAT, GL_FALSE, 0,vertices);
    nResult = GL_ERROR_CHECK((GL_NO_ERROR, "glVertexAttribPointer(position, 3, GL_FLOAT, GL_FALSE, 0,vertices);"));

    glEnableVertexAttribArray(glGetAttribLocation(shader_data.psId,"inputtexcoord"));

    glVertexAttribPointer(glGetAttribLocation(shader_data.psId,"inputtexcoord"), 2, GL_FLOAT, GL_FALSE, 0,texcoord);

    glBindTexture(*target11, id1);

    glDrawElements ( GL_TRIANGLES, 36,GL_UNSIGNED_INT, indices );

when i change WIDTH=HEIGHT=2, and call a glreadpixels with height, width equal to 4 in draw_cube() i can see first 2 pixels with white color, next two with blue(glclearcolor), next two white and then blue and so on.. Now when i change width parameter in glTeximage1D to 16 then ideally i should see alternate patches of white and blue right? But its not the case here. why so?