01 August 2024, 16:22 | #61 | |
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Not wishing to resurrect an old thread, but I started tinkering with some old ideas I'd had many aeons ago. I wanted to expand on the rotator I did for Brian the Lion to a full screen roto-zoom like effect, only to discover that Axis had already done something similar in RockLobster. Nevertheless I persevered and created a 320x256, 16 colour 1x1 pixel rotator running at 50fps using the old double shear technique. It's not really a roto-zoom as the zoom is just the usual side-effect from the double shear effect - Axis did comspensate for that in his code, so it's not entirely comparable, and used a C2P approach to doing the vertical shear. However the point of commenting on this thread is that for the vertical shear I'm using a similar technique to what's described here I believe. I shear within a 16 pixel wide block using 4 blitter passes, all at run-time. So unlike the full screen rotator which was incremental, this one can be set to an arbitrary angle at run-time. [ Show youtube player ] I could have 'optimised' it a bit to use fewer passes based on the shear angle, but it wasn't really worth it. It's already cutting down the number of horizontal copies based on shear angle, so in some frames there's a load of blitter time free. But in the worst case I think I'm using about 90% of the frame. I tried triple buffering so that some frames could run over a bit and claw back the time on the lighter frames. But the issue is that it goes in cycles, so I'd need far more than 3 buffers to avoid over-running before I had free frame time to claw it back. Still it can easily be optimised further, for one thing most of my code is written in C, only a few critical functions are hand optimised assembly. I thought at the time, this technique could be used for a sine scroller without even realising it had already been done |
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01 August 2024, 16:26 | #62 |
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That looks great!!!
You should definitely get back into demo coding! |
01 August 2024, 16:45 | #63 |
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01 August 2024, 17:05 | #64 |
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01 August 2024, 18:04 | #65 |
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When I got back into amiga coding (10 years ago now... time flies...), I tried to do bitmap rotation with shears, but I thought you had to use 3 shears. I was not aware of the fact that 2 was enough. I only managed to do a small one in 64x64 pixels or so in one bitplane.
Can only agree with @Dan and @Ross. Awesome, and please make a new demo! |
01 August 2024, 18:52 | #66 |
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Wow! Really cool to see Kreator on here and coding Amiga again!
That full-screen rotator looks very nice. Poking around your youtube channel I also spotted your 256x256x16 rotator, also excellent to see! I made my own tribute to your and Mr.Pets rotators in a recent demo: https://www.pouet.net/prod.php?which=96604 Would be cool to compare notes some day. |
02 August 2024, 13:09 | #67 | |
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02 August 2024, 14:21 | #68 |
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Wowsers, Michael Troughton in the house. It's like having royalty pop over to borrow some tea.
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03 August 2024, 03:28 | #69 | |
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Yeah, it's roughly the same amount but I do need a bit more bitplane dma which soaks up the difference, I went for size over colors. I too have a few spare cycles but no magic to make the blitter faster and no memory left for triple buffering. I did manage to squeeze in copper bar colors to make up for 8 colors and then used some extra cycles to print the greets. It was a lot of fun and I'd been enamored by your Brian effects for 30 years so it felt great to finally make my own. |
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03 August 2024, 09:15 | #70 |
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Kreator!
I cannot count the number of times I stared at Brian the Lion intro rotozoom and wondered if this is A1200-only and how the hell did you make it so fast in 1994 on OCS! I met Dan at Revision and kept asking him if there's a chance you'd come back and release something. The shearing trick was well known in the graphics community since 1986, discovered concurrently by several people and popularized by late prof. Alan Paeth in Graphics Gems 1. Here's a great compilation of different approaches to bitmap rotation by the late Mike Morton, who was also a Graphics Gems contributor: Bitmap Rotation. Here's a scan of the original 1986 Paeth rotation paper. Here's a very nice repo of all the Graphics Gems code. Now on top of that, you have to figure out how to use blitter to do a high-performance Y-shear on Amiga 500. This kind of impressive stuff pushed me into democoding on Amiga in 2020s. You just cannot use standard graphics algorithms as they will run too slow and have to think way out of the box. My self-challenge (ok, might have been a debate with britelite and later gigabates) was a textured tunnel in 50fps and 4bpl on Amiga 500 that I ended up partycoding and releasing at Revision. |
03 August 2024, 09:18 | #71 | |
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03 August 2024, 09:59 | #72 |
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All the effects I put in Brian the Lion were originally for my next Amiga demo,and I had quite a few others in reserve. But when I took them into work, the boss Martin Edmondson immediately wanted them in the game, so we had to find some way of cramming them into a nearly finished game. I wish I had gotten round to doing another demo back then, but by the end of BtL I was no longer writing Amiga stuff at home - I suppose that's what happens when you turn a hobby into a job.
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03 August 2024, 12:33 | #73 |
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One pixel sinus scroller rulez !
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03 August 2024, 20:59 | #74 |
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Yesterday, 12:56 | #75 |
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Today, 10:09 | #76 |
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Rubbed my eyes, pinched myself, slept a night over it, and yeah, it seems to be true: Kreator is creating again. Awesome!
Now and then I take / took a look a Raistlin's site, but so cool you are now back again too. If I remember correctly your coding tutorials in Stolen Data taught me, as being a young and innocent teenager back then, among other things how to rotate a point in 3D; I was so proud and happy I grasped that. I curiously look forward to your demo. This will be a feast. And I hope your previews (the youtube stuff) will be part of it. By the way, what do you mean by "offline precomputed hidden surface removal"??? I reckon it is not about an inversely rotated camera, is it? Based on what you write, it must be something more difficult and sophisticated. |
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