Re: [LogoForum] motion question

At 09:21 1.7.2003 +0200, Erich Neuwirth wrote:
> peter,is there an easy way to pick up a color from a pixel?
> i imported a picture
> and want to change it, so i need to use the colors used in the picture.
> i did not find a tool for clicking on a pixel
> and thelling the pen:
> use this color now.
>
> is there a way to do that?

Erich,

Yes, there are ways.

The picture must be loaded to the background of a pane or page.

Then you can use either the classical turtle procedure dotcolor, which
tells you the color under the turtle's pen. FOr this approach you need to
create a helper turtle, which may be hidden. And on each click you position
it to the place where the user clicked and ask for its dotcolor.

In Imagine there is also a "turtleless" way - each page or pane has a
procedure dotcolorAt :coord which reports the pixel color at a given
coordinate.

You can define this code as the page's onLeftDown event to see the effect:

pr dotcolorAt mousepos

(if you define it for the onClick event then mousepos will be the place
where the user released the mouse button, not where he/she pushed it)

-------

Note that the result of both dotcolor and dotcolorat can be an name of
Imagine color (like "white or "pink or "yellow4) or an [r g b] triple if
the color does not match any of the defined Imagine colors.
If you need to process the colors then you need all of them in the [r g b]
form.
There is a function torgb which input is an Imagine color (Imagine color
name or Comenius Logo color number or [r g b] triple) and the output is an
[r g b ] triple:

? pr torgb [10 10 10]
10 10 10
? pr torgb "yellow4
168 168 0
? pr torgb 10
0 255 0

--------

If your picture is a turtle's shape then you can either change your program
and use a pane instead of the turtle. Or if it is essential to have a
turtle which shape is your picture then you can have in the same time the
same picture loaded to a hidden pane and detect clicks to the turtle while
reading pixels from that hidden pane. Ask for details if you need to use
this approach.

Regards

Peter


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