# Usage

The genplotting library use, as a backend, an external 
[software](https://git.tetalab.org/tTh/libtthimage/src/branch/master/Tools/genplot2.c)
who can be installed with the [libtthimage](https://git.tetalab.org/tTh/libtthimage) and convert scratchfiles to
[Targa](https://en.wikipedia.org/wiki/Truevision_TGA) image file. 

For drawing an *useless graphic*, you have to follow three steps:
initialize, use and terminating.

## Initialize

Call the subroutine `genp_init` with two parameters.
The first is an integer and must be 0. In the futur, it may be used for
setting some predefined configurations. 
 
The second is the filename for recording the plottings instructions,
I'm using the `.scratch` extension for naming this file.
And if this filename is an empty string, *stdout* will be used, so
you can pipe the data for post-processing purpose.
 **Be warned:** if you use this option, don't write anything to the
unit 6 **!**

## Use it

- `real xa, ya, xb, yb`
- `integer color`
- `call genp_move(xa, ya)`
- `call genp_draw(xa, ya, color)`
- `call genp_line(xa, ya, xb, yb, color)`

## Terminator

- `call genp_end(0)`
This procedure end the current plotting, add some *bells* to the *WIP*,
and close the output file, if an output file was specified.

## Rendering

- `subroutine genp_do_render(srcfile, tgafile, xsize, ysize)`

After doing all that useless computing graphics, you can call
the render, only if you have given a filename to `genp_init`.
The render engine that I use can only write Targa file, but
I'm going to add `PNG` to it output in a near futur.