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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: bbond007 on February 16, 2012, 06:50:33 AM
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Hello!
Do AGA amigas such as my 1200 support HAM5?
I have written a program in SAS c 4.68 utilizing HAM5 mode and to my surprise it works on my MINIMIG 1.1 and UAE but not my actual A1200...
I changed the program to use HAM6 and it worked on the A1200.
What gives? This is very discouraging.
Thanks.
Nate
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I never heard of something like HAM5. HAM utilizes either 6 bitplanes (OCS) or 8 bitplanes (AGA).
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I never heard of something like HAM5. HAM utilizes either 6 bitplanes (OCS) or 8 bitplanes (AGA).
In the hardware reference manual it says
"If only five bit-planes are used, the data from the sixth plane is automatically supplied with the value as 0."
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Ok, but it does not make much sense because you can only modify the blue component but not red and green.
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I assume the missing bitplane is in the colour information bits (index or modified value), otherwise it would indeed not be all that useful :)
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No, as far as I can tell from the documentation the missing bitplane(s) are always at the high end - you can't selectively disable them, only enable bitplanes 0-x.
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I assume the missing bitplane is in the colour information bits (index or modified value), otherwise it would indeed not be all that useful :)
Ok, but it does not make much sense because you can only modify the blue component but not red and green.
I assume is just call OpenScreenTags() SA_DISPLAYID:HAM_KEY with SA_DEPTH:5?
HAM5 does indeded work the way Thomas suggests and I do want to just modify the blue value with my HAM pixels, however it does not seem to work on my AGA 1200.
I thought AGA was 100% compatible with OCS? Seems odd they would have left out an entire mode... I must be doing something wrong...
thanks,
nate
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not that odd, what's the use if you can only change blue?? seems more like a hardware bug that was relabled as a feature, then fixed in AGA.
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not that odd, what's the use if you can only change blue?? seems more like a hardware bug that was relabled as a feature, then fixed in AGA.
Not a bug, just a weird artifact mode you get from playing around with the bitplane enable in a mode where the bitplanes have special meaning...
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not that odd, what's the use if you can only change blue?? seems more like a hardware bug that was relabled as a feature, then fixed in AGA.
I do have a use for it. I bet Mrs Beanbag can guess what I'm trying to do...
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Hmm. Some sort of scanline filling cheat?
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@wodan
it's faster than 6 planes and allows 256 (blue-ish) colors, perfect for underwater simulators :-P
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@wodan
it's faster than 6 planes and allows 256 (blue-ish) colors, perfect for underwater simulators :-P
1 bit for HAM mode 4 for the blue level, so 2^4 = 16. AGA would be 64.
Also, You are only altering the blue color component, so the resulting color might not even be blue at all, maybe it has no blue :)
I'll do the underwater simulator next...