Downsampling a texture

OpenGL OpenGL: Basic Coding
1

Hi,
I’m trying to do the post-effect Depth of Field using a deferred shading technique.

My idea is to make a downsample of the final shape image (the one with all the geometry and lights) in orther to apply a gaussian filter more efficiently.
I create a FBO to save this downsampled image, I bind it, I scale the viewport to with / 2 and height /2 and then I paint into it.
The problem I have is instead of painting the whole texture with a “zoom”, it only paints the part that can fill the smaller texture… (I’ll put images to explain
it better).

Here you have the bind in the FBO:


// Binding the DOF buffer
  glBindFramebuffer(GL_FRAMEBUFFER, dof_buffer_.id);

  // Texture with the half of the size to make the downsample.
  glBindTexture(GL_TEXTURE_RECTANGLE, dof_buffer_.tex_id);
  glTexImage2D(GL_TEXTURE_RECTANGLE, 0, GL_RGB32F,
    width / 2, height / 2, 0, GL_RGB,
    GL_FLOAT, NULL);

  glTexParameteri(GL_TEXTURE_RECTANGLE, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
  glTexParameteri(GL_TEXTURE_RECTANGLE, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
  glTexParameteri(GL_TEXTURE_RECTANGLE, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
  glTexParameteri(GL_TEXTURE_RECTANGLE, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

  glBindTexture(GL_TEXTURE_RECTANGLE, 0);

  glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
    GL_TEXTURE_RECTANGLE, dof_buffer_.tex_id, 0);
  // See if framebuffer was created correctly
  GLenum framebuffer_status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
  if (framebuffer_status != GL_FRAMEBUFFER_COMPLETE) {
    tglDebugMessage(GL_DEBUG_SEVERITY_HIGH, " DOF framebuffer bind not complete");
    return false;
  }

  glBindFramebuffer(GL_FRAMEBUFFER, 0);

  return true;

Here you have the code of the render process: (now I’m just testing painting only the ambient texture of the Gbuffer).



//Before DOF I create Gbuffer, quad directional light and pointlights.
...

// DOF effect
    //Downsampling the image.
    glBindFramebuffer(GL_FRAMEBUFFER, dof_buffer_.id);
    glUseProgram(program_dof_downsample_);
    glClear(GL_COLOR_BUFFER_BIT);

    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_RECTANGLE, gbuffer_.tex_ambient_id);
    glUniform1i(glGetUniformLocation(program_dof_downsample_, "texture"), 0);

    glViewport(0, 0, 1280 / 2, 720 / 2);

    glBindVertexArray(light_quad_.vao);
    glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
    glBindTexture(GL_TEXTURE_RECTANGLE, 0);

and here you have the texture, the original and the downsampled:

Original:
[ATTACH=CONFIG]1060[/ATTACH]

Downsampled:
[ATTACH=CONFIG]1059[/ATTACH]

How can I downsample the whole image into a smaller texture??

Thank you very much!