Re: Fix dashed line errors (issue 320320043 by address@hidden)

[Urs Liska]

I currently can't compile so I can't test the patch, and I can only
assess (1) from reading the code.

But it's good to fix this. It's a glitch but nevertheless "feels"
awkward when tweaking a score.
Urs


Am 07.03.2017 um 05:46 schrieb address@hidden:
> Reviewers: ,
>
> Message:
> Please review.  Thanks!
>
> Description:
> Fix dashed line errors
>
> There are two errors in lily/line-interface.cc which cause
> dashed lines to be drawn inaccurately.
>
> (1) Line-thickness is improperly subtracted from the "off"
> value in Line_interface::make_dashed_line.  This was done,
> presumably, to account for the line cap of each dash.  In fact,
> PostScript discounts the line cap when constructing the pattern.
>
> (2) Dashed lines are constructed so that they begin and end
> with a dash.  Thus, a dashed line is built of dash + whitespace
> units and a last lone dash.  Period is not adjusted in
> Line_interface::line for this last dash, which can lead to a
> noticeable difference in its length compared to other dashes.
>
> Correcting these flaws ensures that dashed lines end with a
> dash rather than whitespace, and that terminating dashes are
> not clipped.  Also, the number of dashes drawn reflects the
> number calculated.
>
> Please review this at https://codereview.appspot.com/320320043/
>
> Affected files (+13, -8 lines):
>   M lily/line-interface.cc
>
>
> Index: lily/line-interface.cc
> diff --git a/lily/line-interface.cc b/lily/line-interface.cc
> index
> bc0895339fea3c996e08a71891c0090cbea2e96c..9c16ece4106f956af5cb3a30cb4fc667065abab8
> 100644
> --- a/lily/line-interface.cc
> +++ b/lily/line-interface.cc
> @@ -123,8 +123,8 @@ Line_interface::make_dashed_line (Real thick,
> Offset from, Offset to,
>                                    Real dash_period, Real dash_fraction)
>  {
>    dash_fraction = min (max (dash_fraction, 0.0), 1.0);
> -  Real on = dash_fraction * dash_period;
> -  Real off = max (0.0, dash_period - on - thick);
> +  Real on = dash_fraction * dash_period;
> +  Real off = max (0.0, dash_period - on);
>
>    SCM at = scm_list_n (ly_symbol2scm ("dashed-line"),
>                         scm_from_double (thick),
> @@ -226,16 +226,21 @@ Line_interface::line (Grob *me, Offset from,
> Offset to)
>          return Stencil ();
>
>        Real len = (to - from).length ();
> -
> -      int n = (int) rint ((len - period * fraction) / period);
> -      n = max (0, n);
> -      if (n > 0)
> +      /*
> +        Dashed lines should begin and end with a dash.  Therefore,
> +        there will be one more dash than complete dash + whitespace
> +        units (full periods).
> +      */
> +      int full_period_count =
> +        (int) rint ((len - period * fraction) / period);
> +      full_period_count = max (0, full_period_count);
> +      if (full_period_count > 0)
>          {
>            /*
>              TODO: figure out something intelligent for really short
>              sections.
> -           */
> -          period = ((to - from).length () - period * fraction) / n;
> +          */
> +          period = len / (fraction + full_period_count);
>          }
>        stencil = make_dashed_line (thick, from, to, period, fraction);
>      }
>
>
>
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