Using EHB in reverse patchy fog cloud overlay effect?

[ImmortalA1000]

I wonder if anybody knows of any games or demos where the EHB 6th bitplane has been inverted to allow, for example, twice as bright patches of fog?

The principle is you set your palette to the bright colours that you would need so the darker 32 colours are close to what you want. Obviously a bit of an issue as none of the RGB elements can be higher than 8/16 possible settings but if you were going to do say a Victorian landscape view of London for a Jack the Ripper game it might work. Obviously each frame you have to use an inverted single bitplane monochrome image of say the actual fog cloud shapes.

Also how easy is it to do something like the EHB Fred Astaire over desert scene with Blitz/AMOS+compiler?

My idea is to set screen mode to EHB, load a double width image of said Victorian London scene and somehow manipulate just the 6th bitplane to move essentially a monochrome (1bitplane) double width image with a horizontally tiling mask for the fog clouds and shift that left/right twice as many pixels as I scroll the first 5 bitplanes at a slower speed (half as often changes to screen memory/scroll register etc) or do the clouds in 2 pixel shifts left/right. For maximum effect you could also move the clouds of fog at different speeds using the copper to change the screen position etc.

I was thinking that this was another tick in the 'more like SNES than Megadrive' box for Amiga vs Megadrive vs SNES technical comparison of possible effects.

I am sure both Blitz/AMOS are too slow to do this fast enough for console quality demo but it's just a proof of concept for a video I wanted to do for youtube once my Amiga stuff is 100% set up again permanently. Could be interesting if it affects sprite palette too but I suspect it would not...which is still useful in other ways.

[lmimmfn]

Unfortunately its not possible, the max values in HB mode are 7 for RGB(OCS) therefore you can never make them bright(would require values of 10+ for all RGB).
For what your asking, fog clouds etc. you can have 1 or 2 bitplanes for that cloud layer and have its colours brighter than the others, e.g. 16 colours, add 1 bitplane which has 16 brighter colours and scroll that separately(in a vertical shoot em up for example.)
Its a nice effect and not enough Amiga games make use of it, especially AGA.

[ImmortalA1000]

I don't think I explained it right.

The main picture/background would already be a picture that only used RGB values from 777 to 000 like a murky Victorian scene of London and so you set the palette up so your 32 EHB colours are what your graphics for the background would need to be anyway as a regular 32 colour screen mode and so you automatically get the lighter versions for the fog patches.

The only difference is unlike the Fred Astaire demo where the 6th bitplane is used to draw a shadow you invert the bitmap data for that 6th bitplane so you would get the fog patch shaped highlights not shadows as defined by colours 0-31 being shown where the 6th bitplane value is set to a 0,0,0,0,0,0,0 etc for those pixels and where you want to see the background 'under' the fog the bitplane value would be set to 1.

[lmimmfn]

That would work but the main pic being displayed would be incredibly dark. Its just an inverse of how its normally used.
Better to use a 32 colour screen and have say 16 colours for the background and another 16 colours for clouds and use the 5th bitplane scrolling seperately to provide a cloud effect. Does that make sense?

[ImmortalA1000]

Like I said it's supposed to be for dark murky scenes, if you were going to do a movie game conversion of say Sleepy Hollow it would work great on some title/menu/loading pages I thought whilst watching that last night

It's a trade off for sure but it's something no 286 PC of the OCS Amiga era could manage. Don't forget I only think in terms of real hardware connected to real CRT tubes and not emulation so there is always the contrast/brightness controls on my Trinitron (and you would probably do a display screen to allow people to calibrate their TV controls for optimal use)

My Buck Rogers game looked like crap on my PC in emulation but the 3 colour anim + copperlist animated floor tests looked really nice hooked up to my Sony Trinitron Problem was that it really needed to be coded in 68k AND coded with talent so I abandoned it. Would be much easier to learn demo quality 6502 and VIC-II coding than arcade quality 68k OCS chipset coding! Mind you only a few people ever managed to do arcade quality game engines so I don't feel bad.