feat: color: add channel properties to color plus linear-mix

[flukejones]

Add extra properties to the color type.

• red
• green
• blue
• alpha

Add extra method to the color type

• linear-mix This provides a simple linear mixing of two ARGB colors with a scaling factor

[flukejones]

This is a much cleaned up version of the previous PR with extraneous work pulled out to a separate branch. I think everything is covered, but lets see what the pipeline tests say.

[flukejones]

I'm not sure what this is about:

 /tmp/.tmpmBbGeV.cpp:268:800: error: invalid use of member function ‘uint8_t slint::Color::green() const’ (did you forget the ‘()’ ?)
  268 |                             return [&]{ auto tmp_root_window_1_b2 = self->root_window_1_b2.get();;auto tmp_root_window_1_linearmix = self->root_window_1_linearmix.get();;return ((((((((self->root_window_1_b1.get() == tmp_root_window_1_b2) && (tmp_root_window_1_b2 == self->root_window_1_b5.get())) && (self->root_window_1_b3.get() == slint::Color::from_argb_encoded(+4.278190335e9))) && (slint::Color::from_argb_encoded(+4.29490176e9) == self->root_window_1_r4.get())) && (self->root_window_1_y1.get() == slint::Color::from_argb_uint8(std::clamp(static_cast<float>(1) * 255., 0., 255.), std::clamp(static_cast<int>(255), 0, 255), std::clamp(static_cast<int>((1 * 255)), 0, 255), std::clamp(static_cast<int>(0), 0, 255)))) && (tmp_root_window_1_linearmix.red == 111)) && (tmp_root_window_1_linearmix.green == 156)) && (tmp_root_window_1_linearmix.blue == 68)); }();

Does this mean that the methods and struct fields are in conflict?

[ogoffart]

Thanks a lot for the PR. Some comment inside

[ogoffart]

Do you mean adding an example in code? It's pretty simple - if I change this from interpolate to mix I get a jump when the slider switches to the next colour.

Sorry to insist, but i still don't understand what you mean. (I cannot try your example since it needs a custom Slint)
Would you have a screenshot that shows the difference?

(I've replicated a way to compare different way to mix color currently afailable, but they seem similar: link)

[flukejones]

@ogoffart I must be losing my mind... I could have sworn one was smoother when stepping from one colour to the next. The mix() gives a nicer blend for sure. It seems I've done something somwhere in my own code that now they both give the same effect.

A screenshot doesn't work here as it is the visible movement from one colour to the next in a two colour mix(n, n+1) selected from an array..

I am now non-plussed on whether this part stays in or not. If you prefer to remove it I'm okay with that. Though I do recall the mix() had a lot more calculation done compared to interpolate so maybe that could be a helpful distinction?

[ogoffart]

Yes, please remove the interpolate function, as it is a duplicate of mix and there should be good explanation of the difference in the docs as to when to use one or another. But I think it is not needed to have it.

[ogoffart]

Thanks a lot. Looks good.