Atari XL

184 The Ateri XL Handbook
600 'NEXT PR: REM GO BACK FOR NEXT
PRIORITY
One final point is that in the text mode, mode 0,
and in text windows in other graphics modes, the
text colour is controlled by colour register 2, but the
luminance of the text is controlled by colour
register 1. If a player passes over the text, the text
colour changes to the colour of the player, but its
luminance is unaltered. This means that the text
may disappear if the luminances of the player and
of the text are the same.
COLLISIONS
The final feature of player-missile graphics is that
the GTIA chip can detect collisions between
players, between a player and a missile, and
between players or missiles and the graphics
objects on the main display. These collisions,
which occur when two graphics objects overlap, are
automatically detected and recorded in various
registers. The collision indication registers are
shown in the table opposite. The contents of the
registers have the following meanings:
Missile/Display and Player/Display collisions
Bit 0 set indicates a collision with a display item
coloured by colour register O.
Bit 1 set indicates a collision with a display item
coloured by colour register 1.
Bit 2 set indicates a collision with a display item
coloured by colour register 2. .
Bit 3 set indicates a collision with a display item
coloured by colour register 3.
Missile/Player and Player/Player collisions
Bit 0 set indicates a collision with Player o.
Bit 1 set indicates a collision with Player 1.