On Thu, Mar 26, 2015 at 12:48:45AM -0500, Mark Ventimiglia wrote:
> Selected text is indicated by displaying a rectangle under the selected
> text. When the default background color of dark blue is used for the
> selection rectangle, it does not have sufficient contrast with the default
> text color of black, and the highlighted text cannot be read easily.
>
> To fix this, determine the HSV value of the selection background color.
> Then, set the color of the selected text based on that value -- white if
> the value is less than 0.6, black otherwise. This ensures that there is
> sufficent contrast to make the text readable over the background color.
> Also tag all selected text with secseltext, so that it can be reverted to
> the default color on a change of selection.
Finally got back to looking at this again...
> + foreach t [$canv find withtag secseltext] {
> + $canv itemconf $t -fill $fgcolor
> + $canv dtag $t secseltext
> + }
Why not just:
$canv itemconf secseltext -fill $fgcolor
$canv dtag secseltext
> +proc getseltextcolor {c} {
> + # Get the largest RGB value -- this is the V in HSV
> + set value [lindex [lsort -integer [winfo rgb . $c]] end]
> +
> + # If the normalized value is darker than 0.6 use white text,
> + # otherwise use black text
> + return [expr ($value < (65535 * .6))?"white":"black"]
The HSV value doesn't correlate very well with perceived lightness,
and this will use black text when the background is R=0 G=0 B=153,
which is very hard to read. It would probably be better to use
a weighted sum of R, G and B, maybe something like 0.3R + 0.6G + 0.1B.
Paul.
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