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Old 04 September 2019, 11:39   #1
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Location: Italy
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Custom Screens System (fiddling with AMOS Professional and AGA)

This project has been gathering dust for 16 years, but I have finally decided to at least let Amigans know about it.

Back in 2002 (or early 2003) I got in touch with a developer who had released a nice AMOS Professional game. While chatting with him, I had the idea of developing a fancy Copper trick that would have allowed the game he was currently working on to flip the screen as seen in the level introduction screens of Project-X. The trick was never used (and the game was never released), but little by little it developed into a full video system for AMOS Professional that, by exploiting the AGA chipset, greatly expanded the platform's capabilities. As an added challenge, I decided to implement the system using AMOS Professional itself (eventually, for performance reasons, I implemented a procedure in assembly, but I did resist the temptation of doing the same for other procedures).
Here's how the system documentation introduces the system itself:

The Custom Screens System (CSS) is a system which extends the AMOS Professional screen handling capabilities by exploiting the AGA chipset. It allows to define Custom Screens (CSs), by means of custom Copperlists, that are 100% compatible with the graphic operations (bobs, drawing, texts, buffering, etc.) and that open a wide range of possibilities - most notably non-EHB 64 colors screens and an advanced Dual PlayField mode, named Cross PlayField (XPF).

* up to 8 CSs at once;
* CSs with up to 64 non-EHB colors;
* CSs usable as normal screens for graphic operations;
* CSs display window size and position restricted only by hardware limits;
* scrolling fully supported;
* 35 ns horizontal scrolling granularity;
* extended palette control:
* 24 bit RGB color values (for everything);
* fading from any palette to any other palette;
* palette allocation, mixing, masking, etc.
* XPF:
* up to 8 bitplanes;
* per-color opacity/transparency of the Front CS freely defineable;
* all that can be done with CSs can be done with XPFs, too;
* miscellaneous visual effects;
* miscellaneous utility procedures;
* Copperlist optimization.

The CSs comes in the shape of a collection of procedures written in AMOS Professional itself (except for one written in assembly).

This video shows a what the system was capable of; more specifically, how the system can overlay two indipendent screens (in the examples, the background has a depth of 5 bits and the foreground has a depth of 3 bits, but the depths can be any from 2 to 6, as long as their sum is at most 8), manipulate their palettes and degree of blending, and execute the flip screen effect that got everything started.

[ Show youtube player ]

Although CSS was fully functional and complete with tutorials and documentation, I never distributed it because, at some point, I realized I could have obtained more flexible and performing results by implementing the core idea differently. So, I started a new system from the scratch, called Advanced Video System (AVS). When it was about 80% done, a terrible thing happened: I lost the sources! I managed to recover some older sources, but I felt too bad to restart the development (not to mention that I was about to move country, so I did not have much time left).
In my dreams, one day I'll use CSS to rework two old games of mine, but honestly I don't know if I'll ever have a chance to.

Last edited by saimo; 05 September 2019 at 03:14.
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