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metatag-title=(RASTER AT | ugBASIC User Manual)
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metatag-description=(Manual page for RASTER AT)
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metatag-og:title=(RASTER AT | ugBASIC User Manual) 
metatag-og:description=(Manual page for RASTER AT)
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====== ugBASIC User Manual ======

===== RASTER AT  =====

===== SYNTAX =====
     RASTER AT line WITH label
     RASTER label AT line

==== PURPOSE ====

The ''RASTER AT'' instruction will set the next execution raster line for a
raster routine. A raster routine is a small program or sequence of instructions 
that uses a particular moment in the screen display to be activated. This is 
when the electron beam (the raster beam) scans the screen, line by line, to 
draw the image.

The mechanism is simple. The computer generated an interrupt (a signal that 
stopped the main program being executed) every time the raster beam reached 
the given line on this instruction. When the interrupt occurred, the 
processor passed execution to the raster routine. The routine directly does
something, like modify the video memory o registers. Once the change was 
complete (by using the instruction ''NEXT RASTER''), the processor would 
resume execution of the main program from where it had stopped.

Using this mechanism, programmers could create very simple, but often 
surprisingly engaging, graphics, animations, and games, considering the
hardware limitations of the time. They were essential 
for creating effects such as scrolling, moving sprites around the screen, 
creating explosion or deformation effects. 

Raster routines offers very precise control over image generation, 
allowing for customized and optimized effects, and stimulated 
the creativity of programmers, who could invent new ways to exploit 
the mechanism to create innovative visual effects.






==== EXAMPLE ====
    RASTER AT #&H42 WITH rasterRoutine
    RASTER AT (rasterLine+1) WITH rasterRoutine


==== ABBREVIATION ====
   RstAt


==== AVAILABLE ON ====
  * Commodore 128 (MOS 8502)
  * Commodore 64
  * Commodore VIC-20
  * Commodore 64+REU
  * Commodore PLUS/4


==== SEE ALSO ====
[[NEXT RASTER]] [[NEXT RASTER AT]] 

==== ANY PROBLEM? ====
If you have encountered a problem using this command, if you think there is a bug or the explanation is unclear, please [[https://github.com/spotlessmind1975/ugbasic/issues/new?title=ISSUE ON RASTER AT|open an issue]] for this keyword on GitHub. Thank you!===== POWERED BY =====

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