[Inkscape-devel] SVG pattern questions

23 Aug 2012


      I have a couple of questions related to SVG patterns.
First some background.  After a bit of experimenting I came up with the 
following patterns to match the standard
hatch patterns available in the EMF file type.  Notice that the stroke 
color is hard coded.  The translate 6 lines
are needed to prevent visible discontinuities in the pattern for 
diagonal lines.  (Not needed for the diagonal cross hatch
because the perpendicular lines fill in each other's discontinuities.)
<pattern id="EMFhatch0"
        patternUnits="userSpaceOnUse" width="6" height="6" x="0" y="0"
...
<path d="M 0 0 6 0" style="fill:none;stroke:black" />
     </pattern>
     <pattern id="EMFhatch1"
        patternUnits="userSpaceOnUse" width="6" height="6" x="0" y="0"
...
<path d="M 0 0 0 6" style="fill:none;stroke:black" />
     </pattern>
     <pattern id="EMFhatch2"
        patternUnits="userSpaceOnUse" width="6" height="6" x="0" y="0"  
viewBox="0 0 6 6" preserveAspectRatio="none" >
        <line x1="-1" y1="-1" x2="7" y2="7" stroke="black" 
id="subEMFhatch2"/>
        <use xlink:href="#subEMFhatch2" transform="translate(6,0)"/>
        <use xlink:href="#subEMFhatch2" transform="translate(-6,0)"/>
     </pattern>
     <pattern id="EMFhatch3"
        patternUnits="userSpaceOnUse" width="6" height="6" x="0" y="0"  
viewBox="0 0 6 6" preserveAspectRatio="none" >
        <line x1="-1" y1="7" x2="7" y2="-1" stroke="black" 
id="subEMFhatch3"/>
        <use xlink:href="#subEMFhatch3" transform="translate(6,0)"/>
        <use xlink:href="#subEMFhatch3" transform="translate(-6,0)"/>
     </pattern>
     <pattern id="EMFhatch4"
        patternUnits="userSpaceOnUse" width="6" height="6" x="0" y="0"
...
<path d="M 0 0 6 0 M 0 0 0 6" style="fill:none;stroke:black" />
     </pattern>
     <pattern id="EMFhatch5"
        patternUnits="userSpaceOnUse" width="6" height="6" x="0" y="0"  
viewBox="0 0 6 6" preserveAspectRatio="none" >
        <use xlink:href="#subEMFhatch2" transform="translate(0,0)"/>
        <use xlink:href="#subEMFhatch3" transform="translate(0,0)"/>
     </pattern>
Questions:
1.  Is it possible to inherit or reference the stroke color in the 
pattern?  For instance, this fills a square with the first EMF hatch 
pattern (horizontal lines):
     <path
    style="fill:url(#EMFhatch0); 
fill-rule:evenodd;fill-opacity:1;stroke:#000000;stroke-width:1px;stroke-linecap:square;stroke-linejoin:miter;stroke-miterlimit:8;stroke-dasharray:none;stroke-opacity:1;"
    d="
    M 149.99595 262.49292
    L 172.49535 262.49292
    L 172.49535 284.99231
    L 149.99595 284.99231
    z " />
Stroke in the path style is for the line bounding the square, so it 
isn't available for the fill to reuse.  The "fill"
value is used to reference the pattern, so it isn't available either.  
It would be nice to be able to specify a color other than black for the 
pattern, other than by having to create a second pattern which differs 
only in its stroke value.  In general SVG allows inheritance, but here 
the obvious routes are blocked.  If this isn't possible I guess it will 
come down to naming the patterns like "EMFhatch0_FF0000", with the color 
appended to the name.  (This is in order to avoid having multiple 
defines with different names for the exact same pattern.)
2.  Because of the free form way patterns are defined it looks really, 
really hard to map arbitrary user defined patterns onto the standard set 
of EMF hatch patterns (or CGM, or any other graphics standard that has a 
predefined set).  Is there anything in inkscape presently along these 
lines (pseudocode):
    pattern[i].has_horizontal_lines();  // pattern has horizontal line 
elements
    pattern[i].has_vertical_lines[];
    pattern[i].has_diagonal_lines[];
    pattern[i].has_antidiagonal_lines[];
?
Thanks,
David Mathog
mathog@...1176...
Manager, Sequence Analysis Facility, Biology Division, Caltech