Getting the window size of a projector using Psychtoolbox

Hi

I'm trying to get the window size of my projector when its connected to my Windows laptop and the display extended.

get(groot, 'MonitorPositions') returns the projector size correctly(1280*800)

but Screen('WindowSize', screennumber), probably the function for psychtoolbox, keeps returning 1600*1000.

Does anyone know what is the problem?

WindowSize returns 1280*800 alright when the same projector is connected to my Windows desktop.

[Walter Roberson]

Could you expand on what you mean by the display being extended?

[zzz]

It means that my projector is acting the same as dual monitor.

When I drag my mouse pointer to the edge of my laptop display, the pointer goes into the projector showing the window.

I might have used the wrong word.

Forgive me for my bad English and explanation.