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Forums > C64 Coding > Doubling char lines with stretched sprites over it
2018-09-26 22:32
Digger

Registered: Mar 2005
Posts: 285
Doubling char lines with stretched sprites over it

From VIC article it seems impossible but I thought I'd ask anyway:

Is it possible to have first charline duplicated all the way down (standard line doubling trick with badline skipping) with 8 stretched sprites over it?
Seems like sprite 0 data is fetched right where the line doubling should be triggered (cycle 58).

Have spent already too much time trying to (unsuccessfully) cycle this, thus time to reach out. Cheers!
2018-09-26 22:48
Compyx

Registered: Jan 2005
Posts: 399
You can inhibit the sprite 0 DMA fetch by using 6-cycle instructions (DEC $d016) to open the border and do the proper $d011 writes I think.

Though I'd have to look up old demo parts to make sure I actually put an 8-sprite stretcher in the border and not a 7-sprite stretcher.
2018-09-27 07:27
HCL

Registered: Feb 2003
Posts: 675
You didn't ask for open sideborders, did you?

It is of course possible to double charlines with 8 sprites on top (even stretched using d017), however opening sideborder has not been done with this combination. ..and i have tried :)

I am using it in.. uuuh.. EoD and probably a handful of other demos.
2018-09-27 08:37
Digger

Registered: Mar 2005
Posts: 285
Thanks HCL :) Than I will keep trying.
Yeah, no sideborders, since it's only possible with 7 sprites and line crunching.
2018-09-27 10:59
Krill

Registered: Apr 2002
Posts: 1063
Unless NTSC or PAL-N (Drean) :D
2018-09-27 23:38
HCL

Registered: Feb 2003
Posts: 675
Check the interference circles in Uncensored/BoozeDesign, that's a good (?) example of a sprite-fpp over badline-less bitmap. Timing code at $1100 somewhere..
2018-09-28 08:59
Digger

Registered: Mar 2005
Posts: 285
@HCL: I was actually watching it last night, it's interesting how you shift starting Y positions for each sprite to be able to switch all pointers with one value.
I was thinking to use $d018 for that but seems more memory efficient with your approach, no screen RAM/bank switching needed.
2018-09-28 13:16
Compyx

Registered: Jan 2005
Posts: 399
Quoting HCL
You didn't ask for open sideborders, did you?

It is of course possible to double charlines with 8 sprites on top (even stretched using d017), however opening sideborder has not been done with this combination. ..and i have tried :)

I am using it in.. uuuh.. EoD and probably a handful of other demos.


Oops, I somehow always associate sprite stretching with open borders. :)
That said, I couldn't find any old code of mine using 8 sprites, I sure tried, but never succeeded it seems.
2018-09-28 19:03
dano

Registered: Jul 2004
Posts: 153
Quote: Check the interference circles in Uncensored/BoozeDesign, that's a good (?) example of a sprite-fpp over badline-less bitmap. Timing code at $1100 somewhere..

the sprite stretcher in reluge should use about the same technique i guess (without checking it). :)
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