Did it really take that long?

Yes it did.  Here’s why.  NERD ALERT: this involves a lot of detail and arithmetic that very few people will find interesting.

The flag graphics demo I did for Dr DeMoney and others in 1979 was done on a Tektronix 4027 color graphic terminal. It operated over a serial port at 9600 baud. The computer sent text strings to draw graphics.  They were not information dense.

It had a 640 x 480 resolution pixel display.  It was “the highest resolution” color graphics terminal available at the time.

It used a color look up table (CLUT), with 8 slots. The flag would use the first 3 slots.

Colors were expressed using a hue, lightness and saturation format.  Hue was expressed in degrees around a color circle.  Lightness and saturation were expressed as a percentage.  Although a wide range of colors could be described, it could only render 64.  

The text strings are describe in detail in the 4027a operator’s manual. I had to send

  • GRAPHIC command, GRA, requiring 4 coordinates to place the terminal in graphics mode, 14 characters.
  • an ERASE command,  ERA, to clear the graphics, 14 characters.
  • MAP commands, MAP, to set the colors in the first three color table entries to black, 8 characters each, for a total of 24 characters.
  • Color commands, COL, to set the fill colors used when drawing the polygons,  8 characters each, for a total of 24 characters.
  • 64 POLYGON commands, POL.
    • 14 rectangles, drawing the 13 stripes and the blue field, each requiring 4 coordinates, 24 characters each, for a total of 336 characters.
    • 50 star shaped polygons, each requiring 10 coordinates, 125 characters each, for a total of 6250 characters.
  • MAP commands, MAP, to set the first three color table entries to red, white, and blue, 30 characters each, for a total of 90 characters.

This gives a grand total of 6752 characters.

We could send it 960 characters per second.  It would require roughly 70 seconds to transmit the entire string of commands, roughly 1 minute and 10 seconds. By contrast, the five year old laptop that I rendered the video on, produced an 8 bit / color, 960 x 540 bit rendering, including draw time, in 1.24 seconds. That render contains sky, ground, and a flag pole, as well as the flag.

 

 

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