fixed textheight affects scrolling?

[Mark Waddingham]

On 2020-07-09 09:54, Klaus major-k via use-livecode wrote:
> Hi all,
> 
>> Am 08.07.2020 um 17:51 schrieb Klaus major-k via use-livecode 
>> <use-livecode at lists.runrev.com>:
>> 
>> Hi friends,
>> 
>> strange phenomenon, maybe I am missing something!?
>> LC 9.6 on macOS 10.14.6
>> 
>> I have two fields with all available fonts and each line is formatted 
>> directly
>> in the appropriate font it reads.
>> 
>> I set the FixedLineHeight for ONE field to 28, doesn't matter 
>> actually.
>> 
>> Now I want to select a specific line in the fields with this script:
>> -------------------------------
>> on mouseUp pMouseButton
>>  set the wholematches to TRUE
>>  put lineoffset("Lucida Grande",fld "fonts") into tLine
>>  ## Which is 366 in my fields!
>> 
>>  put the effective textheight of fld "fonts" into tTH
>>  set the scroll of fld "fonts" to tLine*tTH + the height of fld 
>> "fonts"
>>  set the hilitedlines of fld "fonts" to tLine
>> end mouseUp
>> -------------------------------
>> 
>> Works fine for the field WITHOUT fixedlineheigt and selects the line 
>> -> Lucida Grande
>> However the same script used with the field WITH fixedlineheight, it 
>> selects -> Lucida Grande Bold
>> which is the line AFTER "Lucida Grande" and actually line 367!?
>> 
>> What am I overlooking?
>> Thanks for any hints!

I suspect the fact it works in the non-fixedline height case is 
serendipity in this specific case - if line height isn't fixed then each 
line will have a different height based on the fonts (although most will 
be the same if the fontSize is the same)...

LineOffset is 1-based - so the first line has scroll 0ish (ish because 
of field margins etc.) - that's probably the issue with your existing 
code.

There's an easier way I think though which should be independent of any 
field styling (size, font, wrapping)...

You can get the formattedTop of a line - which gives you the 
card-relative y co-ordinate of the top of the including the fields top 
and scroll. So this should do the trick:

    set the scroll of field "fonts" to the scroll of field "fonts" + \
                                       the formattedTop of line tLine of 
field "fonts" - \
                                       the top of field "fonts"

The adjustment is necessary because the scroll value is relative to the 
top-left of the 'content' of the field.

Hope this helps!

Mark.

-- 
Mark Waddingham ~ mark at livecode.com ~ http://www.livecode.com/
LiveCode: Everyone can create apps