'Scanlines' The word 'Scanline' has a slightly different meaning these days to the one I'm used to I always took the word 'Scanline' to describe 1 physical horizontal display line on a monitor, more often these days, when someone talks about a 'Scanline' they are referring to the 'Horizontal Retrace Interval', or (in the case of emulators) faking a low scanrate horizontal retrace interval on a high scanrate monitor To show you what I mean, here's a simplified diagram of how an image is created on any raster monitor |
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In the above diagram the black lines show the 'active' part of the display (i.e. when the electron guns are on) and the grey lines show when the electron guns are inactive and sweeping back in readiness to display the next line of the image (The grey lines represent the Horizontal Retrace Interval or Horizontal Blanking) The most important thing to remember is that the speed of the electron guns sweeping across the display This is where the arcade emulator use of the term 'Scanline' comes into play (DOS) MAME running on a PC monitor attempts to do this in two ways... .by using SVGA modes which draw a blank line every other display line The first of the above is the most successful in replicating a low scanrate arcade monitor The second falls far short - and is also the only option available to all Windows based emulators A tweaked VGA 'Scanline' mode is a closer emulation than a SVGA odd/even line 'Scanline' mode |