I have a laptop with i945 chipset and use the "intel" X driver. The internal display has a resolution of 1280x800 (16:10). The projector is capable of many different resolutions, its LCD has a 4:3 ratio. It does not report its default resolution (no "+" at any resolution in "xrandr" output, the laptop reports 1280x800 as its default resolution:

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till@till-laptop:~$ xrandr
Screen 0: minimum 320 x 200, current 1680 x 1050, maximum 1680 x 1680
VGA connected 1680x1050+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
   1680x1050      60.0* 
   1600x1024      60.2  
   1400x1050      60.0  
   1280x1024      60.0  
   1440x900       59.9  
   1280x960       60.0  
   1360x768       59.8  
   1152x864       75.0     75.0     70.0     60.0  
   1024x768       85.0     75.0     70.1     60.0  
   832x624        74.6  
   800x600        85.1     72.2     75.0     60.3     56.2  
   640x480        85.0     72.8     75.0     59.9  
   720x400        85.0  
   640x400        85.1  
   640x350        85.1  
LVDS connected (normal left inverted right x axis y axis)
   1280x800       52.8 +
   1024x768       85.0     75.0     70.1     60.0  
   832x624        74.6  
   800x600        85.1     72.2     75.0     60.3     56.2  
   640x480        85.0     72.8     75.0     59.9  
   720x400        85.0  
   640x400        85.1  
   640x350        85.1  
TV disconnected (normal left inverted right x axis y axis)
till@till-laptop:~$

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I have no problem to use the projector when I activate and deactivate it supplying all settings explicitly to the xrandr command (projector connected after login):

Activate same image on projector and laptop display:

xrandr --output LVDS --mode 1024x768 --output VGA --mode 1024x768 --same-as LVDS

Back to laptop display in its native resolution:

xrandr --output LVDS --mode 1280x800 --output VGA --off

Projector only in a higher resolution than the laptop (Note: non 4:3 modes give a stretched image):

xrandr --output LVDS --off --output VGA --mode 1680x1050
xrandr --output LVDS --off --output VGA --mode 1280x1024

Now if I plug the projector after logging in and do

xrandr --auto

(or press Fn + F7) the projector gets activated but the resolution not adjusted. The screen stays on 1280x800 and the projector shows a truncated image, of only the 1024x768 upper left pixels. The projector does not tell its default/preferred resolution when it gets probed by X which probably auses the problem when activating it without explicitly specifying the desired resolution.

Strangely enough, fully automatic projector integration works when the projector is plugged while X is started (projector connected before logging in). Then X comes up in clone mode, with the highest resolution of the projector which fits into the preferred resolution of the laptop. On the laptop this resolution is displayed with aspect ratio conserved (black margins at the left and the right). When unplugging the projector the laptop returns to its default resolution and when plugging again, it goes automatically to clone mode.

So automatic projector setup is possible and implemented, only X does not do it when running "xrandr --auto" or pressing Fn + F7.

My suggestion is that if the projector does not report a usable default resolution, that the highest resolution of the projector which still fits into the laptop's preferred resolution gets chosen (and display on the laptop screen aspect-ratio conserving, which means that there can be black margins. If the laptop also does not report a preferred resolution, I suggest to take the highest common resolution of laptop and projector. This assures that one sees the complete projection screen on one's laptop screen to have full control over one's presentation.