Reaction to youtube video, can't seem to comment this over there...

[MiltonW]

The -1 is because you loop from 0. If you want to loop through 3 elements (r,g,b) you could do 'FOR %I=1 TO 3' but then you would need to subtract 1 (times 3) from the memory lookup (e.g. ?(graphics+I%+0 - 3).
The alpha is calculated as a bitwise OR. Lets say r% = 1, and g% = 2, then r% OR g% is 3. It's not the same as r% + g%! If r% is 255 then any OR will be 255. since all its bits are already '1'.
The 'VDU r%, ...' is still in VDU 23,27,1,W%,H%,... It expects the WH4 bytes to follow. 'VDU' is just a synonym for PRINT (or printf if you will). So VDU 23 just sends a 23 to the VDP, and VDU r% sends r% to the VDP.

[lovejoy777]

thanks so much for your clear explanation. it's it ok if I copy this to the comments section to help others, obviously i will give you credit 😁

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On Sun, 14 Jan 2024, 8:00 am MiltonW, ***@***.***> wrote: The -1 is because you loop from 0. If you want to loop through 3 elements (r,g,b) you could do 'FOR %I=1 TO 3' but then you would need to subtract 1 (times 3) from the memory lookup (e.g. ?(graphics+I%+0 - 3). The alpha is calculated as a bitwise OR. Lets say r% = 1, and g% = 2, then r% OR g% is 3. It's not the same as r% + g%! If r% is 255 then any OR will be 255. since all its bits are already '1'. The 'VDU r%, ...' is still in VDU 23,27,1,W%,H%,... It expects the W*H*4 bytes to follow. 'VDU' is just a synonym for PRINT (or printf if you will). So VDU 23 just sends a 23 to the VDP, and VDU r% sends r% to the VDP. — Reply to this email directly, view it on GitHub <#1>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAJ5TLQLVH5AMB23MSFXFUDYOOGCNAVCNFSM6AAAAABBZ5IC5SVHI2DSMVQWIX3LMV43ASLTON2WKOZSGA4DANRSGUYDONI> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>