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Old 15 April 2021, 12:22   #1
Emufr3ak
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Stardust sw scroller - how is it done

I particularly like the sw scroller on the beginning of this game. Thinking about making a starwars scroller myself. I first wanted to use the 102-zoom trick. Made a quick debug session using winuae and it seems this one is not using it. Also noticed some blitter stuff in fill mode going on.


Any ideas on this?
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Old 15 April 2021, 12:24   #2
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Video showing the effect [ Show youtube player ]
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Old 15 April 2021, 12:54   #3
pink^abyss
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Originally Posted by Emufr3ak View Post
I particularly like the sw scroller on the beginning of this game. Thinking about making a starwars scroller myself. I first wanted to use the 102-zoom trick. Made a quick debug session using winuae and it seems this one is not using it. Also noticed some blitter stuff in fill mode going on.


Any ideas on this?
Haven't looked in WinUAE but the effects seems to update only every 3rd frame, so you have plenty of time to make it happen. You could convert your text into a line buffer with xOffsets. Each line contains only the outlines of the characters. Then project these pixels to the screen, line by line (of course only the lines that don't get skipped). Then fill them.
I guess you will need ~6000 pixels for a similar effect.

Another method would be to skip lines with the copper to get the Y axis projected, and to scale the text with a feedback zoomer. Or as you said 102 copper zoom and prescaled text
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Old 15 April 2021, 13:22   #4
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Okay. I just noticed the slow framerate. This makes it a lot easier of course. But who cares as long as it looks good. 102 copper zoom often looks a bit wierd.
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Old 15 April 2021, 14:27   #5
DanScott
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If there's blitter fill going on, they are probably plotting edge points.

You could create a remap table for each level of scale, and eor your edge points (therefore any plotted on top of another, will cancel them out, in the same way you eor lines in a filled 3D object to blitter fill it)

EDIT. That's actually one of the nicest looking Star Wars scrolls I've seend done on A500
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Old 15 April 2021, 15:34   #6
d4rk3lf
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Here is explained very nicely:
https://codetapper.com/amiga/sprite-tricks/stardust/
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Old 15 April 2021, 15:41   #7
roondar
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That's the tunnel effect, the OP is talking about the Star Wars style scroller
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Old 15 April 2021, 16:23   #8
grond
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I guess you just need one highres image of the text (which you can create on the fly using a font and ascii text) and then shrink it in many steps. Store the precalc shrunk images (it's 1 bitplane only) and display always the lines from the corresponding shrunk image with the right width in the corresponding screen line. You just need one copper move per line to adjust the bitplane pointer and for the darkening lines in the rear an additional copper move to dim the colour down from the bright yellow.
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Old 15 April 2021, 16:46   #9
Emufr3ak
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Doesn’t this come to the same memory requirement like as saving the whole effect as animation? This would require several MBs of memory if I unterstand you correctly.
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Old 15 April 2021, 17:35   #10
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Doesn’t this come to the same memory requirement like as saving the whole effect as animation? This would require several MBs of memory if I unterstand you correctly.
I don't think it would be that much because it is just 1 bitplane. The good thing is that you can create the content of this memory from very little storage space on the disk. You just need the text (a few hundred bytes), a font (probably some KBs) and the code to create the image with the highest resolution and code for creating the shrunk images (perhaps 1 KB). The memory you need for the shrunk images can be freed immediately after you displayed the animation. If the series of shrunk images absolutely doesn't fit in the 512KB, you can calculate new shrunk lines in parallel to displaying the old ones because, after all, you never see more than a few lines of ascii text at the same time. This means you can discard the text lines that have scrolled out of view and use that space for calculating the shrunk images of the new text lines.
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Old 15 April 2021, 18:30   #11
Emufr3ak
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Originally Posted by pink^abyss View Post
Haven't looked in WinUAE but the effects seems to update only every 3rd frame, so you have plenty of time to make it happen. You could convert your text into a line buffer with xOffsets. Each line contains only the outlines of the characters. Then project these pixels to the screen, line by line (of course only the lines that don't get skipped). Then fill them.
I guess you will need ~6000 pixels for a similar effect.

Another method would be to skip lines with the copper to get the Y axis projected, and to scale the text with a feedback zoomer. Or as you said 102 copper zoom and prescaled text
6000 pixel still sounds like a lot even for 3 frames.
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