twister effect

[pmc]

Yeah, I realise - like I said, I already have an assembler implementation working.

[h0ffman]

Cheers guys. Been really helpful seeing the asm implementation in action and understanding how it works. Will start to write my own shortly, have some interesting ideas on how to twist stuff up. But well see.

[Codetapper]

Here's a challenge, perhaps impossible! Who knows...

Can anyone create a version with greater than 4 faces that runs in a frame on a 68000? This javascript version has 15 sides and imho looks very slick!

[h0ffman]

Saying things like that round here can seriously eat up peoples free time

[StingRay]

Originally Posted by Codetapper

Here's a challenge, perhaps impossible! Who knows...

Can anyone create a version with greater than 4 faces that runs in a frame on a 68000? This javascript version has 15 sides and imho looks very slick!

Definitely possible and not that much of a challenge. Check the attachment, I made a twister with 8 segments, red part of the screen: raster time still left (on 68000 of course)!

The trick is, of course, to draw the twister as quickly as possible. Hint: The copper is your friend, you'll need a big copperlist.

[h0ffman]

My guess is you pre draw then set the bitplane pointers every line?

Hmmm. I'm not so sure now?

[korruptor]

That's how I did it. I actually assumed all the textured ones I'd seen had been done that way.

[h0ffman]

I've been doing some maths on this, if you wanted to do a full logo in 5 bitplanes, you would need to multiple the number of lines by the number of lines in your logo too.... Would take a LOT of memory!

[korruptor]

Probably want to do Sting's texture map suggestion if you're doing a logo.

I've only done the noddy tube stuff.

[h0ffman]

Still thinking that on a 68000, that would be touch...... pre-calc different width sizes of the logo, then blit those onto the screen.... hmmmmm....

[korruptor]

Yeah, that's interesting, you could pre-calc the texture offsets for each line width. No idea how expensive the blit /copy from there would be.

Can you do anything with the copper / scroll registers per line, to get something similar? Not played with that much.

[Lonewolf10]

Originally Posted by korruptor

Can you do anything with the copper / scroll registers per line, to get something similar? Not played with that much.

Something along those lines may be possible, if some (or all) of the graphics had been predrawn.
I have never attempted a twisting effect yet... next on my list is to try some 3D objects. I already have some code to use for inspiraton

I used the copper to re-set the hardware scroll register (BPLCON1) for each scanline in the credits section of my demo. I was using it to do a sinewave effect on the background image (a dalmatian, of course!).
It turned out pretty cool, but I had to slow it down to update every 3 VBL's, as it ran too fast when updating every VBL.


Regards,
Lonewolf10

[Toni Wilen]

Use very tall pre-drawn sprites that scrolls up or down and only change sprites' X-position using copper? Very cheap (of course means width restrictions)

[h0ffman]

Hey Toni, thats a pretty good idea. Maybe you could pre-calc the twister but set sprites for the textured points!. Not played with sprites yet.

However I did try my first twiseter yesterday, failed just on the pre-draw

[h0ffman]

Well, I finally worked out what I was doing wrong and got my twister up and running. Borrowed line draw from Sting's example and bumped it up to 5 bitplanes.

It seems the more splits you add, the more like plasma it becomes...

Should run on a 68000, however the copper pointer generation is as yet to be optimised!

EXE attached (not packed this time!)

[StingRay]

Originally Posted by h0ffman

My guess is you pre draw then set the bitplane pointers every line?

Hmmm. I'm not so sure now?

Yep, that's exactly what I'm doing. You first draw the twister to a static bitmap (precalc) and in your main routine you decide which line to copy from that very picture. You have to do that for every line of course. Drawing a textured twister works exactly the same way, i.e. no sprites needed.

[h0ffman]

My big aim is to have a full length logo twisting on one of the faces, which would mean

pre-calc twister * number of lines of the logo = massive!

So I was thinking of pre-calcing the logo widths as sprites then plotting them in position on each line with a sprite....

But... I never dun nuffink wiv spritez

[StingRay]

Originally Posted by h0ffman

My big aim is to have a full length logo twisting on one of the faces, which would mean

pre-calc twister * number of lines of the logo = massive!

You need: static twister pic (e.g. 320*256*5 in your case = 51200 bytes) plus the waits+bpl pointers in the copperlist: 256*(8*5+4) (8*5 = bitplane pointers for 5 bitplanes, +4 = copper wait). Not that massive.

[h0ffman]

Ez Stinger

But, the logo would be different on each line, thus multiplying the twister by the number of lines of the logo surely??

[Coagulus]

Originally Posted by StingRay

Yep, that's exactly what I'm doing. You first draw the twister to a static bitmap (precalc) and in your main routine you decide which line to copy from that very picture. You have to do that for every line of course. Drawing a textured twister works exactly the same way, i.e. no sprites needed.

haha, that's how my rubbish initial attempt at a twister started, with a precalc-ed bitmap and lines copied from it. But I'd got everything else wrong! Thanks again for your help.

loving this thread. It's probably one of the best resources on the net about it now. Now how about all the other effects....