Add 'Invert' tool

[ace-dent]

Invert pixel values 0>1, 1>0.

[Pharap]

This is easier than some of the other suggestions, so I'll look into it when I have the time.

Unfortunately I don't have as much time to spare now as I did back at the start of August.

(Also, it would be an 'action button' rather than a 'tool', in the terminology of the project.)

[Pharap]

To Do:

• Define invert function:

  static Color Invert(Color colour)
  {
      var red = (byte.MaxValue - colour.R);
      var green = (byte.MaxValue - colour.G);
      var blue = (byte.MaxValue - colour.B);
  
      return Color.FromARGB(colour.A, red, green, blue);
  }

• Create Invert.png graphic (32x32 and 16x16)
• Add 'Invert' button

[ace-dent]

Inspiration for icon design: https://www.flaticon.com/free-icon/invert-colors-button_61136 https://www.flaticon.com/free-icon/invert-tool_74155 https://www.flaticon.com/free-icon/invert_7663545

[Pharap]

As much as I appreciate the links, I had already had a look around and made some before mentioning that it was on my todo list.

Specifically I threw "Invert colour icon" at DuckDuckGo, it spat these out, and I ruled out quite a lot of them.

Oddly enough I did actually consider something similar to that first one, but I wasn't sure if it was easy enough to derive the purpose from the image (there's no real sense of 'action'), and I tend to put my own twist on things anyway, so I don't have to worry about copyright.

---

I actually came here to show off my current candidates:

A: B: C: D:

Scaled up versions if you can't be bothered to zoom in:

A: B: C: D:

(You may want to view them separately because GitHub's white background doesn't do them justice.)

I think A and D look the nicest, but C is the easiest to understand the meaning of.

I'm also considering something like:

E:

Which matches in better with existing examples, but I was worred the red and green might confuse people.

[Pharap]

Three more for good measure: F: G: H:

[Pharap]

By the way, the icon is actually the only thing that remains to be done. The actual implementation of the invert action only took a few moments.

---

It did briefly cross my mind that it might be useful to provide an invert tool (not action) that could invert a selected rectangular area instead of just the whole image. But that would take a fair bit longer and I'm not sure it's worth the effort.

[ace-dent]

They look great! My vote is H, then A, then G.