user-defined painting tools

 21.7.16: adde/graphics/user-defined painting tools:

. all the painting tools in the graphics editor

come with high-level instructions (adda code)

that users can copy and modify 

for coding their own tools.

. your brush can have a parameters page of your own design 

not just the usual tool width, flow density, etc.

. each tool is launching a subprogram

that can have any number of novel parameters.

. the usual brush is the function

pen(x,y) -> print (x,y),

but you can invoke a function of your own design

that can print or do anything given pen(x,y),

and your routine can also be a function of

what is already near (x,y);

eg, you can have a stroke that uses a darker or lighter

version of the current color;

or, it can make changes like ipad.ArtSet4's blender tool

where a stroke of the pen decides how to 

move or change any paint that is nearby.

[7.17: 

. when the brush lays down random changes for you,

you can ask for a repeating of that function:

it keeps applying differing random sequences,

so then you can pick the one you like best.]

[7.17: object-oriented vs raster images:

. it can save a paint-stroke object, 

so at any later time you can go into object mode,

and it will show you what objects are used

to paint a certain region,

and you can ask to re-apply an object

to vary the random sequences it provides.]

complement mode:

. any tool providing a certain brush shape

can be used in eraser or complement mode:

the erase function uses the same brush shape,

but removes paint instead of adding paint.

. the complement mode does that too,

but also adds paint where a tool is removing paint.

sketch filler tool:

. make tools that are a function of a sketch;

given a rough sketch, the sketch filler tool will

use your sketch as input for a painting

that your routine generates.