How do you get an ST or STe to display more than 16 colours at once?

[Megalomaniac]

Sorry if this has been asked before, but I'm always intrigued by the relative handful of games which exceed the theoretical limitation of only 16 colours on the screen, especially for moving graphics - Captain Blood uses 29, Wings of Death has 26 in game (and even more in the linking screens), Wrath of the Demon has 57, for example. Sleepwalker on the STe is an extreme example, that has more colours in game than the Amiga 1200 version. How was it done? It's noticeable that the number of colours is usually slightly less than a full palette of 32/64/96 colours, are the duplicated colours used as a mask of some sort?

Edited July 8 by Megalomaniac

[snarkdluG]

You can change the palette on each scanline. 

[JamesWD]

Alot of info on that on DML's website :

 

https://www.leonik.net/dml/sec_crypto.py

 

 

[zzip]

Basically the secret to doing this on any computer is to change the colors in the palette while the screen is drawing.   But this needs to be controlled to get the result you want.

 

As mentioned above, a common way is to set an interrupt at the start of a new line to make palette changes.   This way your game logic loop doesn't need to waste time counting cycles and can focus on the game.    Unfortunately this doesn't seem to be as well-documented as Display List Interrupts on the Atari 8-bits, but it's a similar concept.

 

It's also possible to change colors in the middle of a line,  like Spectrum-512 puts over 40 colors per line.   But here you need to time the color changes yourself and it's CPU-intensive, so not a great approach for games that need performance.

 

Another way is to flash between two images with slightly different colors, and you can blend them.   This can create the illusion of many colors on screen, but causes flicker.   When done well, you will barely notice the flicker,  when done poorly the flicker will be obvious.