how to subtract colors?

[Stauricus]

hello everybody
i have an opaque object, and now i want to lessen it's alpha value.
there is no overload to the '-' operator, and trying something like

text_box.setFillColor(text_box.getFillColor() + sf::Color(0, 0, 0, -15));

doesn't work.

so, how can i subtract 15 from the alpha value? this is in a loop, to be subtracted by this amount many times.
thanks in advance!

[Ixrec]

What exactly do you mean by "doesn't work"?  What's the error message?

[FRex]

What exactly do you mean by "doesn't work"?

-15 silently wraps around to be 241 because it's unsigned char and that's what all unsigned types are supposed to do(wrap around)
Just overload global operator- yourself(not too good) or write own subtraction function(much better).

[Stauricus]

What exactly do you mean by "doesn't work"?  What's the error message?

there's no error message. it adds 15, instead of subtracting it.

-15 silently wraps around to be 241 because it's unsigned char and that's what all unsigned types are supposed to do(wrap around)

ok, not a bad idea. but how am i going to acess the alpha value from a color, since getFillColor() will obviously not work?

[Ixrec]

The docs say r, g, b and a are public attributes of an sf::Color, so you should just be able to use ".a" to get at it.

[Laurent]

There's an operator - for sf::Color in the current development version.

[Stauricus]

The docs say r, g, b and a are public attributes of an sf::Color, so you should just be able to use ".a" to get at it.

yeah, but the color isn't a public attribute from the Shape class, and the only setter method I found is "setFillColor", which sets all colors at once.
maybe something like

text_box.setFillColor(sf::Color(text_box.getFillColor().r, text_box.getFillColor().g,  text_box.getFillColor().b,  text_box.getFillColor().a - 15));

would work, but i did something simpler:

sf::Color color(text_box.getFillColor());
color.a-=15;
text_box.setFillColor(color);

There's an operator - for sf::Color in the current development version.

ok, thanks for the info


and thanks everybody for the help