Twisted Brain Demo

[hexwab]

You can see my own experiments in stable rasters back in this thread from last year viewtopic.php?f=53&t=13382 (in which I do give you due credit, doh!)

I remember this thread! I remember thinking it should be possible to get better than 10px horizontal resolution. 20px should be easy enough, just have 20 "ST[AX] &FE21" instructions and self-modify which register to store. You might need to store an entire frame's worth of instructions as I'm not sure where you'd find the time to update them during hblank. Then I got to thinking it should be possible to do better still, and that the limiting factor was finding a font that only had horizontal transitions >=4px apart, and musing about a compiler that would turn such a font and a bunch of characters to draw into a sequence of palette writes and nops, and then I never got round to implementing it or even commenting. But I was definitely watching with interest.

I admit I am in awe of you for actually finishing what you start, particularly huge projects such as PoP

Also thanks for crediting me, and don't worry about it. Revisiting my original post and seeing that at the time I'd credited tricky for the vsync, er, sync idea, I was completely unable to find *where* I'd apparently seen mention of it before. Attribution is hard.

Tom.

[lurkio]

... If you're not familiar with the demo, check it out here.

Noticed some glitches in the Twisted Brain demo when running it on my Master 128 which has the VL68C45 chip installed, which was recently found to be problematic. Screenshots of the glitches are attached to this post. Lee also has the VL68C45 in his Master, and sees the same glitches on his machine.

[lurkio]

... If you're not familiar with the demo, check it out here.

Noticed some glitches in the Twisted Brain demo when running it on my Master 128 which has the VL68C45 chip installed, which was recently found to be problematic. Screenshots of the glitches are attached to this post. Lee also has the VL68C45 in his Master, and sees the same glitches on his machine.

Photo of the 6845 variant in my Master 128

Photo of the 6845 variant in Lee's Master 128

[VectorEyes]

Eek! I'm really going to have to get Twisted Brain running on my Master which has a Toshiba CRT chip, to add another data point. (Just as soon as it comes back from having its shiny new VideoNULA fitted!)

[streaks]

The twisted columns blew my mind. I read the explanation and was like "aaaaaaaaaaah!". I wouldn't have thought of that. That was mint. btw, BeebEm emu, BBC Master, music cut out early on and got a few weird artifacts on some of the wavey stuff. Might just be my settings. When the smiley sound came on I cacked myself because it was so quiet with my earphones in.

Ridiculous that this can exist for the BBC. Impressed.

[litwr]

In some ways this demo is better than the best demos for 8-bit Commodore.

[kieranhj]

Thanks for the kind words both. Unfortunately BeebEm is the least accurate BBC emulator available (from a low-level cycle timing POV) so I provide no warranty when using it I'm afraid! Try b-em or jsbeeb for the emulated experiece (I haven't tried b2 as yet, sorry Tom) or, better still, real hardware and a CRT monitor.

I'm hoping to uncover & fix the VLSI CRTC variant timing problem at ABUG in September. I'll post an update if so.

[Kevin Edwards]

Is BeebEm still being actively maintained? It would be nice if the cycle timings could be fixed to bring it up-to-date like B-Em ( big ask I know).

I know some of my 6522 critical stuff fails on BeebEm. It also fails to run ( unprotected ) LunarJetman correctly - it uses 6522 timiers for a split screen palette change which is broken.

I can record 'real-time' .mp4 video from BeebEm easily, but B-Em is not happy about this. I record videos for my YouTube channel and Twitter feed using BeebEm but can't record some of the timing critical games which is a shame.

Cheers,
Kevin.

[uniforix]

Abosolutely amazing. Would have loved this to be around back in the day, great work!! Mind blown.

[dominicbeesley]

Thanks for this excellent and inspiring write up. I love a walk through code like this and I really appreciate the time you've taken to offer up your secrets!

D