Differences

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--- centering_20the_20graphics_20origin [2018/03/31 13:19] – external edit 127.0.0.1
+++ centering_20the_20graphics_20origin [2024/01/05 00:22] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
 =====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:\\
+//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.