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color bending on a coco II
Posted: Thu May 07, 2015 6:03 pm
by simon
Been experimenting a bit with bending the colors on my coco II...
results so far (totally stable / NO flicker)
i will post more when i gain more control over the results.....
/Simon
Re: color bending on a coco II
Posted: Thu May 07, 2015 9:32 pm
by simon
did a *bit* more twiddle....
the green colorset reveals other colors....
know more tomorrow
Re: color bending on a coco II
Posted: Fri May 08, 2015 6:38 pm
by simon
more testing
Re: color bending on a coco II
Posted: Fri May 08, 2015 8:18 pm
by Bosco
Up to your normal tricks I see.
So what is colour bending?
Re: color bending on a coco II
Posted: Fri May 08, 2015 10:23 pm
by simon
Bosco m8...
try to combine pmode 3/4 on a per line basis...
pmode 4 is 256*192 and the colorburst is surpressed... BUT if you fiddle it so you shift to another colorburst in the border, then hey presto... more color....
varying the duration / phase of the colorburst varies the hue... so say 1line pmode3, 1 line pmode4 or 2 lines pmode4 1 line pmode 3 etc etc
different modes give different results....
PAL has a nasty habit of correcting the phase on alternate lines, so we not gonna achieve as many colors as NTSC, and we not gonna get artifacts either....
but given some careful timing (i'm still experimenting) we can actually achieve multiple shades that are previously unseen....
and it's NOT gonna flicker AT ALL !
/Simon
Re: color bending on a coco II
Posted: Sun May 10, 2015 12:13 pm
by Bosco
Sounds like Alchemy to me.
Re: color bending on a coco II
Posted: Sun May 10, 2015 12:38 pm
by sorchard
Bosco wrote:Sounds like Alchemy to me
I think you're right. SJ is doing a great job of discovering new ways of messing with the hardware. I always thought the Dragon/Coco chipset was boring and well behaved. Apparently not!
Re: color bending on a coco II
Posted: Wed May 13, 2015 5:57 pm
by simon
hmmmm....
more experiments
this time the color bled into the border.....
Re: color bending on a coco II
Posted: Thu May 14, 2015 9:00 pm
by simon
more colorbend experiments suggest a pattern emerging
seems the PAL vdg implementation does totally supress the colorburst in pmode4 (as was intended but not totally on NTSC)
but on a PAL coco II there are 50 extra lines (VDG is NTSC) as padding
these 50 lines have hsync + colorburst enabled
on a dragon 64 the 50 lines are dead hsync wise
SO.... *if* i desync the display and push the 50 lines into the active display area, then i get other colors !
still experimenting this provides me with a *band* of color
not useful for much more than some kind of logo or something
BUT i also found i could push that color into the horizontal borders