=====Centering the graphics origin=====

//by Richard Russell, October 2010//\\ \\  The following code will centre the graphics origin both horizontally and vertically, irrespective of the size and shape of the window:

<code bb4w>
        VDU 26
        IF POS REM SDL thread sync (needed in BBCSDL only)
        ORIGIN @vdu.tr%,@vdu.tb%
</code>

The reason it works is that after a **VDU 26** both the text and graphics viewports fill the entire window (client area). In that case **@vdu.tr%** and **@vdu.tb%** return the width and height of the text viewport in pixels, and since **one** pixel is equivalent to **two** BBC BASIC graphics units they also correspond to **half the width** and **half the height** of the graphics viewport, respectively. Therefore they are the correct values to use for centering the origin.