C64 Demos peek - Fast horizontal bitmap scrolling

In this demos peek video, we look at fast Commodore 64 bitmap scrolling using HSP/DMA delay.
All three parts as one video: • C64 Demos peek - Fast ...
Vertical scroll: • C64 Demos peek - Fast ...
Any direction scroll: • C64 Demos peek - Fast ...
Example code: github.com/mar...
Codebase link: codebase64.org...
Debugging details text file: github.com/mar...

[@herrbonk3635]

Wow!, those easy to use tools you got impressed me more than the scrolling method. No wonder modern "demos" are more impressive than in the 80s.

[@JamesGood]

Thanks, always wondered how these things worked!

[@MartinPiper6502]

Glad to help!

[@mrg8472]

Hello, the row on the top of the sprites are for masking, some sort of drawing artifacts?

[@MartinPiper6502]

Yes, if the top of the sprites are cleared (made transparent) then the top line of the screen shows some unintended graphics.

[@maxusboostus]

Some demo coders say that using VSP can damage some of the old VIC chips. I assume they have proof of this to believe it. The demo called "Next Level" by Performers boasts it doesn't use VSP.

[@MartinPiper6502]

I've never seen any reliable evidence of the C64 VIC being harmed by this. There was a poke on the old Commodore PET that could cause damage due to video hardware timing, but that's not going to work on the C64 since the video hardware is different.

[@ArneChristianRosenfeldt]

The VSP bug is due to race conditions. It is logic problem. Logic is implemented in nMOS logic. Pull up transistors limit the current to protect the chip. VIC is not fighting with the CPU over the address bus. Rather the powerful push pull driver just repeats the logic signal. Ah, of course a push pull (like in TTL) gets hotter on ever edge. Any transients should be latched by the 2 MHz clock, though.