   drawing geometry twice without z-clear
  hi,I use color picking to be able to select triangles in my ogl application. for user feadback I simply redraw the triangles that have been selected in a different color. while the user is in selection mode, the original unselected image is stored in an auxiliary buffer and copied over into the back buffer (glCopyPixels) before rendering the selected triangles. the problem is that I can not see the selected triangles (not even z-fighting artifacts) without clearing the z-buffer first. I have tried PolygonOffset and DepthOffset (maybe not correctly?) without succsess. maybe the glCopyPixels messes with the z-buffer? I have no idea right now where I could look for the cause of the problem, do you have any suggestions? here is some code I'm using:  if(!selectionMode)    drawColorBuffer();  //draw the image into GL_AUX0  glCopyPixels(0, 0, ww, wh, GL_COLOR);  //copy image from GL_AUX0 to GL_BACK  if(selectionIndices){  //draw selected triangles    //glClear(GL_DEPTH_BUFFER_BIT);    glLoadMatrixf(cam.getModelMatrix());    glEnable(GL_BLEND);    glColor4f(1.0f, 0.0f, 0.0f, 0.25f);    glEnableClientState(GL_VERTEX_ARRAY);    glVertexPointer(3, GL_FLOAT, 0, triangleList->glVertices);    glDepthRange(0.0f,0.9f);    glDrawElements(GL_TRIANGLES, selectionIndices, GL_UNSIGNED_INT, selectionIndexList);    glDepthRange(0.1f,1.0f);    glDisableClientState(GL_VERTEX_ARRAY);    glDisable(GL_BLEND);  }