How to achieve 'donut holes' with paths in

问题:

I'd like to draw a shape which has holes in it such that I can fill the shape it and not have the holes filled with that colour (leave them transparent).

According to the W3 path spec:

Compound paths (i.e., a path with multiple subpaths) are possible to allow effects such as "donut holes" in objects.

Can somebody please give a very simple example of how to perform this with a vector path in Raphael?

Thanks very much.

回答1:

This turns out to be quite straightforward if you know the trick. For example this doesn't work:

paper.path("M 50 50 L 50 150 L 150 150 L 150 50 z" + 
          " M 75 75 L 75 125 L 125 125 L 125 75 z")
.attr("fill", "#f00");

But this does work*:

paper.path("M 50 50 L 50 150 L 150 150 L 150 50 z" +
          " M 75 75 L 125 75 L 125 125 L 75 125 z")
.attr("fill", "#f00");

The difference is that for the donut to appear the the inner path has to have it's vertices drawn in reverse order to the outer path (ie. draw one clockwise, the other anti-clockwise). A tidbit I found on the text.xml.svg.devel archives.

(*) At least, it works in Chrome, Opera and Firefox 4.0 beta, but not in 3.6

回答2:

To make this work in Firefox 3.6, you need to close the hole; i.e. make the coordinates join back to themselves when defining the inner boundary. Curiously, this doesn't appear necessary for the outer boundary.

paper.path("M 50 50 L 50 150 L 150 150 L 150 50 z" +
          " M 75 75 L 125 75 L 125 125 L 75 125 L 75 75 z")
.attr("fill", "#f00");

Just a quick note to follow up on the comment - the clockwise/counter-clockwise concept might seem strange at first, but it's pretty standard throughout GIS / CAD technologies.

回答3:

I think the correct way to do this is setting the attribute "fill-rule" to the value "evenodd". Take a look at the svg spec:

Don't try to set it with "Raphael.Element.attr()". It doesn't work. I use the jQuery.attr() function instead:

// assuming paper is a Raphael.Paper object
path = paper.path('Mx,y{some path commands for the main shape}Z'
                  +'Mx,y{some path commands for the hole}Z'
);

// this doesn't work
path.attr({'fill-rule': 'evenodd'});
// neither this
path.attr({fillRule: 'evenodd'});

// if you inspect the object returned by paper.path
// you can see it has a reference to the DOM element
console.debug(path)

// so a bit of jQuery and it's done
$(path[0]).attr('fill-rule', 'evenodd');

I have used this on complex paths with successful results.

回答4:

For anyone looking to do circular donuts, great easy plugin Raphael-donut-plugin

Gist:

Raphael.fn.donut = function(x, y, innerRadius, outerRadius) {
  y -= outerRadius;
  return this.path('M'+x+' '+y+'a'+outerRadius+' '+outerRadius +
      ' 0 1 0 1 0m-1 '+
      (outerRadius - innerRadius)+
      'a'+innerRadius+' '+innerRadius+
      ' 0 1 1 -1 0');
};