CHAN_B% (#ch, offset) and
CHAN_W% (#ch, offset) and
CHANS (DIY Toolkit - Vol C)
These three functions can be used to look at values within the channel definition block relating to the specified channel (#ch). You will need a good book on the QL’s operating system to understand the various offsets, such as the QDOS/SMS Reference Manual (See section 18.7 to 18.9.3 in that book).
They allow you to read single bytes, words and longwords from the channel definition block (what is required depends upon the offset).
Extra offsets (negative numbers) are added by the Pointer Environment which can also be looked at by using these functions.
Instead of using SCR_BASE, you can use:
PRINT CHAN_L (#1,50)
to find the base address of the screen.
100 PRINT 'Window #1's size is'; 110 PRINT CHAN_W% (#1,28);'x'; CHAN_W% (#1,30);'a'; CHAN_W% (#1,24);'x'; CHAN_W% (#1,26)
CHBASE can be used to find out similar information.