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5.3
Display with Grid
A graphic may be displayed with the current score grid, rather than on a blank
screen. Special effects such as a transparent grid are also possible with careful
colour manipulation.
In its simplest form, a graphic can overlay the grid. Where the graphic is colour 0,
the grid will show through. Such sequences may only use the first 64 locations in
the palette, as the top two bits are used by the score grid. In Animator, use the
SQUEEZE option in the palette menu to reduce the number of colours to 64. If you
then view the palette you will see that only the first 64 locations in the palette have
been used, the remainder should be blank. The palette consists of 8 rows of 32
colours, numbered from left to right, and top to bottom. Although only 64 colours
are used, each colour can still be chosen from the 256K colours available. Ensure
that all frames in the sequence use this new palette.
When the sequence is packed, select the
Palette Copy
option, and the first 64
colours will be copied to the remaining colours in such a way as to make the
graphic overlay the grid.
Special effects such as a transparent grid, or a graphic that appears in front of the
grid but behind the scores, or moves in and out of the grid, can be achieved by
manually setting the palette in your GIF file. Palette copying in
Pack
should NOT
be used in these cases.
To achieve such results, it is necessary to understand how the grid is drawn over
the graphic.
Each pixel contains eight bits, giving 256 colours. The top two bits are used for the
score grid, the remaining six being set by the graphic. This allows 64 colours for
the graphic, and 4 for the grid. The four grid colours are 0 for the background, 1 for
scores, 2 for names, and 3 for the grid.
Therefore, the colour that a pixel will appear when it overlays the background is
just the colour of the pixel in the graphic. But when the pixel overlays a score, it
will appear as the colour of the pixel plus 64 (bit 6 set). When it overlays a name it
will appear as the pixel 128 (bit 7 set), and when it overlays the grid as
pixel 192 (bit 6 and 7 set) .
The whole graphic will appear in colours 0-63 when overlaying the background,
64-127 when overlaying the scores, 128-191 when overlaying the names and
192-256 when overlaying the grid. When palette copying in Pack is used, these
four groups of colours are identical, and thus the graphic appears in the same