ASCII-Art function plotting, advice needed...

Hi!

I hope my question is on-topic and not too scientific. I want to
write a tiny ASCII-Art function plotter that outputs graphics like
the following (this sample has been done manually, it's just a proof
of concept and the result of fiddling with different characters for
the function plot):

>                  sin(x) for x ranging from -3 to 3
>   ______________________________________________________________  1
>  |                             |           _-"""""-_         |
>  |                             |         _"         -_       |
>  |                             |       _"             -      |
>  |                             |      -                "_    |
>  |                             |     -                   _   |_
>  |                             |    -                     -  |
>  |                             |   "                       - |
>  |                             |  "                         -|
>  |                             |_"                           -
>  |___________________________________________________________|__  0
>  |                            _|                             |
>  -                           _ |                             |
>  |-                         _  |                             |
>  | -                       _   |                             |
>  |  "                     _    |                             |
>  |   "                   -     |                             |_
>  |    "_                -      |                             |
>  |      -             _"       |                             |
>  |       "_         _-         |                             |
>  |_________"-_____-"___________|_____________________________|__ -1
>  |    '    |    '    |    '    |    '    |    '    |    '    |
> -3        -2        -1         0         1         2         3

The idea of achieving a good vertical resolution is mapping

[0.000, 0.025) to '_', [0.025, 0.075) to '-', [0.075, 0.100) to '"'.

(left boundary included, right one excluded that is) - note that the
above plot may slightly differ from this mapping; it was done
manually and to err is human.

Anybody has a better mapping? Forget about '^' or similar characters
that look very different in different fonts - I can't control the
font that is used. The ideal mapping would take into account not only
the value at a given point but also the left and right neighbor
(which is an approximation for the slope).

The output is meant to be generated automatically so I need fixed
mapping rules. Anybody can provide such rules?

Before I forget it: The output is meant to fit 80x24 (actually 79x24
that is); note that I didn't use full width because there has to be
some space left for numbers with more digits.

You wonder what this plotter is good for? The idea is to make a
server output status diagrams even if there is no 'real' graphics
available.

Josef 'Jupp' Schugt

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