Sigh - that makes sense. One issue is that the resulting paths it
generates are much more "verbose" than they need to be. This would
generally mean that it takes far more storage than it would otherwise
need - and it means that if the result needs to be transformed then it
would take many more computations to transform each segment than the
bezier.
So, perhaps it would be worth having it check the type of the output
and
do either a bezier or a bunch of lines depending on if it is a PC2D or
a
LineSink?
Also, it isn't really that difficult to for Renderer to include its
own
Cubic/Quadratic flattening code, but it might involve more
calculations
than the round-cap code since it would have to be written for
arbitrary
beziers whereas if you know it is a quarter circle then it is easier
to
know how far to subdivide... :-(
...jim
Denis Lila wrote:
So, I have been thinking about this, and I can't see a good
way to do it that wouldn't involve heavy changes to Pisces.
In order for Stroker to generate Bezier quarter circles, it would
have to implement a curveTo method, which means Stroker should
start implementing PathConsumer2D and instead of using a LineSink
output it would have to use a PathConsumer2D output (either that,
or
LineSink should include a curveTo method, but then there won't
really
be any difference between a LineSink and a PathConsumer2D. By the
way,
LineSink doesn't have any implemented methods, so why is it an
abstract
class as opposed to an interface?)
Stroker is used in 3 ways:
1. As an implementation of BasicStroke's createStrokedShape method.
This
uses a Path2D object as output.
2. As a way of feeding a PathConsumer2D without calling
createStrokedShape
to generate an intermediate Shape. This uses a PathConsumer2D
output.
3. As a way of feeding lines to a Renderer object, which generates
alpha
tiles used for anti-aliasing that are fed to a cache and extracted
as needed
by an AATileGenerator. Obviously, Stroker's output here is a
Renderer.
1 and 2 aren't problems, because the underlying output objects
support
Bezier curves. 3, however, doesn't, and it seems like implementing a
curveTo method for Renderer would be very difficult because the way
it
generates alpha tiles is by scanning the drawn edges with
horizontal
scan lines, and for each scan line finding the x-intersections of
the scan
lines and the edges. Then it determines the alpha values (I'm not
too sure
how it does this).
In order to implement Bezier curves in Renderer, we would have to
have
a quick way of computing, for each scan line, all its intersections
with
however many Bezier curves are being drawn.
I haven't given much thought to how this could be done, as I am not
very
familiar with Bezier curves, but it doesn't seem easy enough to
justify
fixing such a small bug.
----- Original Message -----
From: "Jim Graham" <james.gra...@oracle.com>
To: "Denis Lila" <dl...@redhat.com>
Cc: 2d-dev@openjdk.java.net
Sent: Wednesday, June 9, 2010 7:42:33 PM GMT -05:00 US/Canada
Eastern
Subject: Re: [OpenJDK 2D-Dev] Fix for drawing round endcaps on
scaled lines.
I don't understand - why do we generate sample points based on the
size
of the cap? Why not generate a pair of bezier quarter-circles and
let
the rasterizer deal with sampling?
...jim
Denis Lila wrote:
Hello.
I think I have a fix for this bug:
http://icedtea.classpath.org/bugzilla/show_bug.cgi?id=506
Basically, the problem is that if there is a magnifying affine
transformation set on the graphics object and one tries to draw a line
with small thickness and round end caps, the end caps appear jagged.
This is because the computation of the length of the array that
contains the points on the "pen" with which the decoration is drawn
does not take into account the size of the pen after the magnification
of the affine transformation. So, for example, if the line length was
set to 1, and the transformation was a scaling by 10, the resulting
pen would have a diameter of 10, but only 3 pen points would be
computed (pi*untransformedLineWidth), so the end cap looks like a
triangle.
My fix computes an approximation of the circumference of the
transformed pen (which is an ellipse) and uses that as the number of
points on the pen. The approximation is crude, but it is simple,
faster than alternatives
(http://en.wikipedia.org/wiki/Ellipse#Circumference), and I can say
from observations that it works fairly well.
There is also icing on the cake, in the form of slight improvements
in performance when the scaling is a zooming out. Example: if the
original line width was 100, but g2d.scale(0.1,0.1) was set, then the
resulting line would have a width of 10, so only ~31 points are
necessary for the decoration to look like a circle, but without this
patch, about 314 points are computed (and a line is emitted to each
one of them).
I appreciate any feedback.
Regards,
Denis Lila.
