Relationship between linecap and dashes

[Regina Henschel]

Hi all,

perhaps someone has an idea how to solve the problems with round dashes.

The problems are
(1)
LibreOffice applies the linecap not only to the true line ends, but to 
the dashes too. That might result in contradiction between DashStyle and 
LineCap (UNO enums). LibreOffice ignores the draw:style attribute of 
draw:stroke-dash element in ODF file format, it depends rounding of 
dashes on linecap. I see such behavior too in other application, which 
all do not have a special rounding attribute for the dashes. That 
includes MS Office, Corel Draw, Scribus and Browsers(SVG). But 
LibreOffice uses the DashStyle enum in several switches in the code and 
DashStyle is a published enum.
(2)
LibreOffice adds the linecap to the dash length and reduces the space 
between the dashes. I see that behavior in Browser(SVG), CorelDraw and 
Scribus too. But MS Office rounds the dashes themselves without taken 
any part of the space between the dashes.

You can skip the description below. It is only if you need some details.

Kind regards
Regina

ODF defines the dash pattern in the styles.xml file. For example
   <draw:stroke-dash draw:name="Var3Dot2Dash" draw:style="rect"
     draw:dots1="3" draw:dots1-length="100%"
     draw:dots2="2" draw:dots2-length="300%" draw:distance="150%"/>
or
   <draw:stroke-dash draw:name="Fix1Dash2Dot" draw:style="round"
     draw:dots1="1" draw:dots1-length="0.5cm"
     draw:dots2="2" draw:dots2-length="1.5cm" draw:distance="0.3cm"/>

The line style itself has in its graphic-properties (relevant attributes 
only) for example
    draw:stroke="dash"
    draw:stroke-dash="Var3Dot2Dash"
    svg:stroke-width="0.6cm"
    svg:stroke-linecap="round
Or
   draw:stroke="dash"
   draw:stroke-dash="Fix1Dash2Dot"
   svg:stroke-width="0.6cm"
   svg:stroke-linecap="flat"

Possible values of draw:style attribute in the pattern are "rect" and 
"round".
Possible values of svg:stroke-linecap in the line style are "flat", 
"square" and "round".
 From this definition, you would expect, that rounding of dashes is only 
defined by the pattern and rounding of the line ends is defined by the 
linecap.

UNO has the enum DashStyle in com::sun::star::drawing with values
{ RECT, ROUND, RECTRELATIVE, ROUNDRELATIVE }
RELATIVE corresponds to the ability to have dash length relative to line 
width or not. That exists in ODF too as you see in the examples.
And UNO has the struct LineDash with its components
DOTS, DOTLEN, DASHES, DASHLEN, DISTANCE.
The naming DOT and DASH is misleading, because always DOT corresponds to 
'dots1' of ODF, and DASH corresponds to 'dot2', regardless of the length 
given in DOTLEN and DASHLEN.
For linecaps exists the enum LineCap { BUTT, ROUND, SQUARE }. BUTT means 
the same as "flat".

OOXML has the line attribute cap, with values rnd (round), sq (square), 
flat. OOXML describes the dashing pattern with a sequence of Dash Stops 
elements, each with Dash length and Space length, all length values 
relative to line width. Despite of 'dot' in the names od prstDash 
presets, there exists no special pattern element 'dot'.

SVG describes the line cap in the stroke-linecap attribute and the 
pattern in a stroke-dasharray attribute, which too has dash&space pairs. 
SVG uses length with unit and percent values.

VML (Fallback in Word) uses the stroke element with attributes dashstyle 
and endcap. The pattern is a series of number pairs for dash length and 
space length, relative to line width. VML has some preset names with 
'dot', but here too the pattern does not provide a special 'dot' item.