The Edge Flag Algorithm—A Fill Method for Raster Scan Displays

Bryan D. Agkland, Neil H. Weste

Research output: Contribution to journalArticlepeer-review

58 Citations (Scopus)


Contour (polygon) filling is a primitive required in many application areas of raster scan graphics. The bit-map memory in a frame-store display is computationally well suited to this task, as it provides a large scratch pad working space. In this paper, a number of contour filling algorithms based on the read/write properties of the frame-store memory are compared with the classical “ordered-edge-list” approach. Performance is evaluated on a microcomputer controlled frame-store display system in terms of ability to fill correctly, execution speed and processor memory requirements. A new algorithm, based on a more exact definition of an object edge, is presented. This algorithm, denoted edge flag algorithm, is implemented within the frame-store memory. It features high speed, in conjunction with minimal CPU memory requirements, making it ideally suited to hardware or microcode (firmware) implementation.

Original languageEnglish
Pages (from-to)41-48
Number of pages8
JournalIEEE Transactions on Computers
Issue number1
Publication statusPublished - 1981
Externally publishedYes


  • Animation
  • filled colored shapes
  • frame-store
  • graphics
  • polygon fill
  • raster scan


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