#211 Implement Spectrum SE 64 colour mode on SDL backend

[Gilberto Almeida]

- Implement the Spec SE 64 colour mode (on SDL backend only).
+ Added a uidisplay_plot8_64() that extends the existing uidisplay_plot8() and uses the full ATTR byte rather than just separate INK and PAPER.
+ Added clut_update_palette() to sync SE's CLUT with SDL's RGB palette.

[Gilberto Almeida]

[Fredrick Meunier]

The ULA+ has a fixed 256 colour palette, I'd suggest that should just be assigned in each UI instead of the existing 16 colour palette and then you could use the existing uidisplay_plot8 to draw pixels. clut_update_palette() would also then not be required.

[Gilberto Almeida]

I don't quite see what you mean, maybe you can give me a few more pointers?
I was not happy with having to replace uidisplay_plot8, but it was the only way I could think of making it work, as I am not familiarized with FUSE's source code.
I'd like to add this feature with as little changes to FUSE as possible, so I'll rework the code according to your indications.

[Fredrick Meunier]

The standard Fuse code has a 16 colour palette in each UI corresponding to the standard Spectrum colour scheme (e.g. for SDL colour_values[]). The proposed ULA+ has a fixed 256 colour palette instead (with up to 64 colours "active" at one time), so this could be supported by extending e.g. colour_values[] to 256 entries for the full palette of the ULA+.

The ink and paper arguments to uidisplay_plot8() are indexes to the above array, so uidisplay_plot8() would not need to be otherwise modified to handle plotting in all the ULA+ colours. The code that maps the attribute to a colour index in the above array in display.c display_parse_attr() would need to be aware of the CLUT indexes. I'd suggest making this function a function pointer like the flashing function (see display_dirty_flashing_fn in display.h).