On 18.12.20 13:50, Pratyush Yadav wrote:
> On 17/12/20 11:14PM, Stefan Haller wrote:
>> On 17.12.20 22:49, Pratyush Yadav wrote:
>>> Hi,
>>>
>>> On 24/11/20 10:23PM, Stefan Haller wrote>>>> +proc convert_rgb_to_gray {rgb} {
>>>> + # Simply take the average of red, green and blue. This wouldn't be good
>>>> + # enough for, say, converting a photo to grayscale, but for this simple
>>>> + # purpose of approximating the brightness of a color it's good enough.
>>>> + lassign [winfo rgb . $rgb] r g b
>>>
>>> Is there no simpler way to extract r, g, and b? This is a little cryptic
>>> to be honest.
>>
>> Actually, I find this pretty elegant, and from what I have seen, it's
>> idiomatic Tcl. A less cryptic way would be (untested):
>>
>> set components [winfo rgb . $rgb]
>> set r [lindex $components 0]
>> set g [lindex $components 1]
>> set b [lindex $components 2]
>>
>> But I much prefer the one-line version.
>
> I agree. Using lassign is much neater. But that is not my point. I am
> talking about the "[winfo rgb . $rgb]". This call generates the list
> that is then assigned to the 3 variables. This part is a little cryptic.
> Is there no simpler way to separate out the r, g, and b values?
According to the winfo man page this is the only way to do this;
see [1].
Instead of the lassign, you can also do
foreach {r g b} [winfo rgb . $rgb] {}
but I don't think that's better.
-Stefan
[1] https://www.tcl.tk/man/tcl8.6/TkCmd/winfo.htm
