[SOLVED] OpenGL glDrawBuffer and glBindTexture

OpenGL glDrawBuffer and glBindTexture

I'm still new on opengl3 and I'm trying to create a multipass rendering.
In order to do that, I created FBO, generated several textures and attached them to it with

    unsigned index_col = 0;
    for (index_col = 0; index_col < nbr_textures;  ++index_col) 
            glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + index_col, texture_colors[index_col], 0);

It works well (I try to believe that I'm doing good here!).

My comprehension problem occurs after, when I try to render in the first texture offscreen, then in the second texture, then render on the screen.
To render to a particular texture, I'm using :

FBO.bind();
glDrawBuffer(GL_COLOR_ATTACHMENT0);
glBindTexture(GL_TEXTURE_2D, FBO.getColorTextures(0)); //getColorTextures(0) is texture_colors[0]

Then I draw, using my shader, and after I would like to do :

glDrawBuffer(GL_COLOR_ATTACHMENT1);
glBindTexture(GL_TEXTURE_2D, FBO.getColorTextures(1));

and after all

glBindFramebuffer(GL_FRAMEBUFFER, 0);
RenderToScreen(); // assuming this function render to screen with a quad

My question is : What is the difference between glDrawBuffer and glBindTexture? Is it necessary to call both? Aren't textures attached to buffer? (I can't test it actually, because I'm trying to make it works...)

Thanks!

Solution

glBindTexture is connecting a texture with a texture sampler unit for reading. glDrawBuffer selects the destination for drawing writes. If you want to select a texture as rendering target use glDrawBuffer on the color attachment the texture is attached to; and make sure that none of the texture sampler units it is currently bound to is used as a shader input! The result of creating a feedback loop is undefined.