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Elite on the BBC Micro

Version analysis of TVT3

This code appears in the following versions (click to see it in the source code):

Code variations between these versions are shown below.

Name: TVT3 Type: Variable Category: Screen mode Summary: Palette data for the mode 1 part of the screen (the top part)
The following table contains four different mode 1 palettes, each of which sets a four-colour palatte for the top part of the screen. Mode 1 supports four colours on-screen and in Elite colour 0 is always set to black, so each of the palettes in this table defines the three other colours (1 to 3). There is some consistency between the palettes: * Colour 0 is always black * Colour 1 (#YELLOW) is always yellow * Colour 2 (#RED) is normally red-like (i.e. red or magenta) ... except in the title screen palette, when it is white * Colour 3 (#CYAN) is always cyan-like (i.e. white or cyan) The configuration variables of #YELLOW, #RED and #CYAN are a bit misleading, but if you think of them in terms of hue rather than specific colours, they work reasonably well (outside of the title screen palette, anyway). The palettes are set in the IRQ1 handler that implements the split screen

Code variation 1 of 6A variation in the comments only

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Master

6502SP

mode, and can be changed by calling the SETVDU19 routine to set the offset to the new palette in this table.
mode, and can be changed by the parasite sending a #SETVDU19 <offset> command to point to the offset of the new palette in this table.
This table must start on a page boundary (i.e. an address that ends in two zeroes in hexadecimal). In the release version of the game TVT3 is at &2C00.

Code variation 2 of 6A variation in the comments only

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Master

6502SP

This is so the SETVDU19 routine can switch palettes properly, as it does this
This is so the #SETVDU19 command can switch palettes properly, as it does this
by overwriting the low byte of the palette data address with a new offset, so the low byte for first palette's address must be 0. Palette data is given as a set of bytes, with each byte mapping a logical colour to a physical one. In each byte, the logical colour is given in bits 4-7 and the physical colour in bits 0-3. See p.379 of the Advanced User Guide for details of how palette mapping works, as in modes 1 and 2 we have to do multiple palette commands to change the colours correctly, and the physical colour value is EOR'd with 7, just to make things even more confusing.
.TVT3 EQUB &00, &34 \ 1 = yellow, 2 = red, 3 = cyan (space view) EQUB &24, &17 \

Code variation 3 of 6A variation in the comments only

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Master

6502SP

EQUB &74, &64 \ Set with a call to SETVDU19 with A = 0, after which:
EQUB &74, &64 \ Set with a #SETVDU19 0 command, after which:
 EQUB &57, &47          \
 EQUB &B1, &A1          \   #YELLOW = yellow
 EQUB &96, &86          \   #RED    = red
 EQUB &F1, &E1          \   #CYAN   = cyan
 EQUB &D6, &C6          \   #GREEN  = cyan/yellow stripe
                        \   #WHITE  = cyan/red stripe

 EQUB &00, &34          \ 1 = yellow, 2 = red, 3 = white (chart view)
 EQUB &24, &17          \

Code variation 4 of 6A variation in the comments only

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Master

6502SP

EQUB &74, &64 \ Set with a call to SETVDU19 with A = 16, after which:
EQUB &74, &64 \ Set with a #SETVDU19 16 command, after which:
 EQUB &57, &47          \
 EQUB &B0, &A0          \   #YELLOW = yellow
 EQUB &96, &86          \   #RED    = red
 EQUB &F0, &E0          \   #CYAN   = white
 EQUB &D6, &C6          \   #GREEN  = white/yellow stripe
                        \   #WHITE  = white/red stripe

 EQUB &00, &34          \ 1 = yellow, 2 = white, 3 = cyan (title screen)
 EQUB &24, &17          \

Code variation 5 of 6A variation in the comments only

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Master

6502SP

EQUB &74, &64 \ Set with a call to SETVDU19 with A = 32, after which:
EQUB &74, &64 \ Set with a #SETVDU19 32 command, after which:
 EQUB &57, &47          \
 EQUB &B1, &A1          \   #YELLOW = yellow
 EQUB &90, &80          \   #RED    = white
 EQUB &F1, &E1          \   #CYAN   = cyan
 EQUB &D0, &C0          \   #GREEN  = cyan/yellow stripe
                        \   #WHITE  = cyan/white stripe

 EQUB &00, &34          \ 1 = yellow, 2 = magenta, 3 = white (trade view)
 EQUB &24, &17          \

Code variation 6 of 6A variation in the comments only

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Master

6502SP

EQUB &74, &64 \ Set with a call to SETVDU19 with A = 48, after which:
EQUB &74, &64 \ Set with a #SETVDU19 48 command, after which:
 EQUB &57, &47          \
 EQUB &B0, &A0          \   #YELLOW = yellow
 EQUB &92, &82          \   #RED    = magenta
 EQUB &F0, &E0          \   #CYAN   = white
 EQUB &D2, &C2          \   #GREEN  = white/yellow stripe
                        \   #WHITE  = white/magenta stripe

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