#283 Opacity option

[William Kendrick]

Provide an opacity choice, which can be utilized by certain tools:

• Paint
• Stamp
• Lines
• Shapes
• Certain Magic tools
  • The API would need to be extended so that Magic tools can report whether or not they support it

Any drawing done with these tools would then be blitted to the canvas with the chosen opacity (whereas right now they are always 100%). That is, allow some tools to apply their effects semi-transparently.

I imagine this could be a kind of multi-option button, that cycles through some presets (100%, 75%, 50%, 25%). It could either appear within the "Colors" horizontal bar of buttons or, probably better would be at the bottom of the right-side vertical list of tool options (i.e., where we currently show the "from center" vs "from corner" options for Shapes, the spacing choice for Paint and Lines, and the rotation, flip, and mirror options for Stamps).

This would be a feature that could be disabled via a configuration file or command-line option, say, --noopacity (and expose it in Tux Paint Config. under Simplification->Control Simplification).

[William Kendrick]

See also https://sourceforge.net/p/tuxpaint/feature-requests/284/ "Blend Options"