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[🎥 suggested: animation showing raster bars changing colour mid-frame]

Overview

Raster tricks rely on synchronising code with the VIC-II’s electron beam. By running instructions on precise scanlines, programmers can change colours, scroll values, and sprite positions mid-frame—creating effects the hardware wasn’t “supposed” to do.

Fast facts

  • Raster interrupts: writing to $D011/$D012 and enabling $D01A fires an IRQ when the beam hits a chosen line.
  • Split screens: update background colours or character sets during the IRQ to create HUDs and “status bars.”
  • Sprite multiplexing: reposition sprites after they’ve been drawn so they reappear lower down the screen, effectively increasing the sprite count.

Lesson connections

  • BASIC Block 6 hints at timing limits that raster tricks later exploit.
  • Transition course introduces interrupt fundamentals preparing learners for assembly-level control.
  • Assembly Acts II–IV walk through practical raster interrupt routines, from colour bars to full-screen scrollers.

See also