Properly design the "filters" tool

[maoschanz]

Use case

The code is ugly, not modular, and the UI is a manual repetition of widgets. It makes filters hard to implement or improve, and probably not very cool to use

Suggested solution

yet another state pattern:

• ToolFilters should have a simpler operation dict, with a filter_id, most other attributes would be there depending on the filter used;
• ToolFilters would have a dict which associates each filter_id to an implementation of AbstractFilter:
  • write AbstractFilter, which has at least a method that will be called in build_operation, and one in do_tool_operation;
  • implementation for blur
  • implementation for transparency
  • implementation for contrast
  • implementation for saturation & veil
  • implementation for "invert colors"
    • it would be easy to add dozens of filters with just [operator]+[color]+[context.paint()]
  • [ ] it would be easy to add a "sharpen" effect with some combination of blur and contrast it isn't
  • it would be easy to add an "emboss" effect with some combination of blur, invert and transparency
  • [ ] it would be easy to add a "glow" effect with some combination of blur and transparency it is, but it's not as useful as expected
• menus would still be manually written, so each filter might corresponds to as many items as pertinent (+ they can define options, like the blur direction)
• the option pane would be built with methods from each filter,
  • either with a method packing anything needed,
  • or, assuming a spinbtn is enough, a method setting its adjustment/tooltip/label/icon/visibility.

Possible drawbacks

it should stay responsive and simple...

the biggest drawback imo is that it's not really modular with manually built menus