Interesting HAM appearance effect needed

[Asman]

I checked my docs and found information ( unknown author ) about that trick.


How can you cheat to have more than the two hardware playfields?

Well, there are more than one way to do this :

One way is to use the blitter to put two of the 'fields' on top
of eachother, ie. two of them use the same playfield. This means
they must use the same colours aswell.

Another technic that is used in many games, is to use the sprites as one
of the playfields. LEANDER, RISKY WOODS and many more use this technic.
The whole secret about this is to use the copper to change the x-position
of the sprites, so that one sprite can be displayed more than once on
each horizontal scan-line. In this way it's possible to have two
'playfields' with 16 colours in each. The problem is that you don't have
the time to change the sprites bitmap-data aswell, so in the playfield
with sprites you must repeat the graphics every 128 pixels in the
x-direction. And if you use more than 4 biplanes, you steal some cycles
from the copper, and then you don't have the time to replace all the
sprites. Here's a copper example of how to replace the sprites :

dc.w	$2C37,$FFFE			; Wait for y = $2c , x = $37
dc.w	$0140,$0040,$0144,$xxxx		; New xpos and data for sprite0
dc.w	$0148,$0048,$014C,$xxxx		; New xpos and data for sprite1
dc.w	$0140,$0050,$0144,$xxxx		; New xpos and data for sprite0
dc.w	$0148,$0058,$014C,$xxxx		; New xpos and data for sprite1
dc.w	$0140,$0060,$0144,$xxxx		; New xpos and data for sprite0
dc.w	$0148,$0068,$014C,$xxxx		; New xpos and data for sprite1
dc.w	$0140,$0070,$0144,$xxxx		; New xpos and data for sprite0
dc.w	$0148,$0078,$014C,$xxxx		; New xpos and data for sprite1

repeat until you reach the end of the screen at x = $D0, and then do this
for each scan-line.

With the above copperlist, you can have a one-bitplane scroller across the
screen without using any bitplanes, and you still have 6 sprites free!

Regards

[Asman]

I checked that trick for HAM6 mode and don't work, mean there is no sprites on screen. For 4 bitplane screen works fine. So its mean that my idea to cover screen by sprite(s) don't work on HAM6

[Toni Wilen]

Originally Posted by Asman

I checked that trick for HAM6 mode and don't work, mean there is no sprites on screen. For 4 bitplane screen works fine. So its mean that my idea to cover screen by sprite(s) don't work on HAM6

Probably nothing to do with HAM6 but 6 bitplanes taking too much DMA time (not enough time for copper to update registers, 1/2 time compared to 4 planes)

[Asman]

Originally Posted by Toni Wilen

Probably nothing to do with HAM6 but 6 bitplanes taking too much DMA time (not enough time for copper to update registers, 1/2 time compared to 4 planes)

You're probably right, I checked that trick for 6 bitplane screen (non HAM6) too and still don't work.

[ElB]

Originally Posted by Codetapper

Fading the screen in cannot be done (that I know of) because it will only fade up the base colours and all the colour adjustment pixels end up looking bizarre.

You can do a HAM fade -- I've seen it done before somewhere, but I can't for the life of me remember where it was, and I have no idea how it worked anyway so it's a bit of a useless observation, other than to provide inspiration to try and figure it out. (Discard the LSB, shift the planes along one, and recalc the base palette maybe?)

[ElB]

Originally Posted by Codetapper

Fading the screen in cannot be done (that I know of) because it will only fade up the base colours and all the colour adjustment pixels end up looking bizarre.

You can do a HAM fade -- I've seen it done before somewhere, but I can't for the life of me remember where it was, and I have no idea how it worked anyway so it's a bit of a useless observation, other than to provide inspiration to try and figure it out. (Discard the LSB, shift the planes along one, and recalc the base palette maybe?)

[Samurai_Crow]

In AmosPro using the AMCAF extension there is a HAM Fade instruction. That proves that it's possible. The catch is finding out how Chris Hodges did it.

[OddbOd]

Unfortuantely AMCAF can only fade HAM to black not the other way around.