Nice, less math.
I think the outside alignment approach will only work on paths that have
a 100% opacity fill.
The off-screen rectangle approach could work with opacity but it has the
same problem with transparent pixels between the stroke and the fill as
you'd get with a custom path once it curves.
It would be nice if Canvas took care of stroke alignment so we can get
rid of the hacks and limitations those bring along.
--
Nick
Op 20-7-2010 19:36, David Flanagan schreef:
Nick wrote:
Canvas would benefit from a way to set stroke alignment. With the
only available alignment being center, which is not very useful,
custom paths have to be drawn to mimic inside and outside stroke
alignment. That workaround may give unwanted transparency on pixels
between a path and its stroke path once a path goes diagonal or curves.
Having Canvas take care of stroke alignment (center, inside and
outside) by adding something like strokeAlign can fix these
transparency problems and makes adding strokes a lot easier and more
useful.
--
Nick Stakenburg
Currently for inside alignment, I think you can do this, with no
computation of custom path:
c.save();
c.clip();
c.lineWidth *= 2;
c.stroke();
c.restore();
Outside alignment is easy if you're also going to fill the path, of
course. But if you want to leave the inside of the path untouched you
could do something like this, I think:
var url = canvas.toDataURL(); // Back up canvas content
var img = document.createElement("img");
img.src = url;
c.save();
c.linewidth *= 2;
c.stroke();
c.clip();
c.drawImage(img, 0, 0); // Restore original bitmap inside the path
c.restore();
You can't use getImageData()/putImageData() for this, since they
ignore the clipping region.
Another approach for outside stroke alignment, if you know the
directionality of your path would be to turn the path inside out by
drawing an off-screen rectangle around the canvas in the opposite
direction. Then the outside of your path becomes the inside of the
new path and you can use the technique above for inside alignment...
David
