Re: GPVAL_TERM_XSIZE behavior?

[Allin C. <cot...@wf...>]

On Fri, 5 Jun 2020, Ethan A Merritt wrote:

> On Friday, 5 June 2020 09:47:49 PDT Allin Cottrell wrote:
>> I'm seeing something that puzzles me. I create a plot using this
>> term line:
>>
>> set term pngcairo size 762,600
>>
>> Now I'm interested in retrieving the size of the PNG (which the
>> venerable xv tells me really is 762 x 600). Using gnuplot 5.0.6 I
>> get
>>
>> GPVAL_TERM_XSIZE = 15240
>> GPVAL_TERM_YSIZE = 12000
>> GPVAL_TERM_SCALE = 20
>>
>> and on division by 20 I get the size back OK. But using 5.2.8 I get
>>
>> GPVAL_TERM_XSIZE = 15220
>> GPVAL_TERM_YSIZE = 11980
>> GPVAL_TERM_SCALE = 20
>>
>> giving 761 x 599 on division by 20.
>>
>> Is this inadvertant or is there a reason for the difference?
>
> 600 pixels on y numbered from 0 to 599.
> 762 pixels on x numbered from 0 to 761.
>
> The internal variables are
>  term->xmax
>  term->ymax
>
> It is perhaps unfortunate that the exported versions are named
> "size" rather than "max".  This change fixed a long history of bug
> reports of asymmetry in the left/right top/bottom borders of
> pixel-based output plots.
>
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%
> commit 6abd6679ae4757fbff54d4cbbb50b12ec35792d3
> Author: Ethan A Merritt <merritt@u.washington.edu>
> Date:   Fri Jun 8 10:42:22 2018 -0700
>
>    Reconcile cairo terminal pixel coordinates and floating point coordinates.
>
>    The floating point coordinate space used internally by the terminal
>    is [0:size*oversample] but in terms of screen pixels it is [0:size-1].
>    Simply casting to (int) produces a bottom-of-screen y coordinate that
>    is one too large and hence is not drawn.  Similarly the right-of-screen
>    maximum x coordinate. Now we report one pixel smaller dimensions back
>    to the core code via term->xmax and term->ymax while retaining the full
>    canvas size internally to retain the oversampling boost in precision.
>    This affects all the cairo terminal variants including wxt.
>
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Thanks, Ethan. Not crucial, but do you know what was the first 
release to incorporate this change? (I tried to figure this out 
myself but failed.)

Allin