do AGA machines support HAM5 mode?

[bbond007]

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

[Thomas]

I never heard of something like HAM5. HAM utilizes either 6 bitplanes (OCS) or 8 bitplanes (AGA).

[psxphill]

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."
 

[Thomas]

Ok, but it does not make much sense because you can only modify the blue component but not red and green.

[wodan]

I assume the missing bitplane is in the colour information bits (index or modified value), otherwise it would indeed not be all that useful

[commodorejohn]

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.

[bbond007]

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

[wodan]

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.

[commodorejohn]

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...

[bbond007]

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...

[Karlos]

Hmm. Some sort of scanline filling cheat?

[Crumb]

@wodan
it's faster than 6 planes and allows 256 (blue-ish) colors, perfect for underwater simulators :-P

[bbond007]

@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...