48 The statement VDU 24 is used (with some numbers after it) to set up a graphics window ( VDU stands for Visual Display Unit). For the window shown above the full statement is VDU 24,a;b;c;d; Note: There is a comma after the 24 and a semi-colon after all the other values. The reason for this punctuation is given in chapter 34. So for our actual graphics window we would put VDU 24,0;100;300;799; In all screen modes which can support easily defined graphics the range of values for a, b, c and d is always the same: 0-1023 vertically, 0-1279 horizontally.
Making a text window Unlike graphics, text ‘starts’ at the top left hand corner of the screen, so text windows are defined using that point as zero. Imagine the text window has edges a, b, c and d ‘text units’ away from the top left of the screen, as shown: The statement VDU 28 is used to set up the window as follows: VDU 28,a,b,c,d Note: There is a comma after the 28 and between the other values. There is no comma at the end. For the text window we wanted to set up, the statement would be To prove that you now have two separate windows try VDU 28,5,24,19,0 COLOUR 129 CLS