[OpenJDK 2D-Dev] Bug in pisces Stroker (div by zero)

[Mark Wielaard]

Hi,

There is a bug in the pisces Stroker in finish(). When ldx and ldy are
so small (zero) that lineLength() will return zero, then you will get a
div by zero exception.

You can see this with for example this webstart application (you will
need to have IcedTeaWebstart [netx] installed):
http://linuxhippy.blogspot.com/2008/11/jgears2-rendermark.html

java.lang.ArithmeticException: / by zero
  at sun.java2d.pisces.Stroker.finish(Stroker.java:698)
  at sun.java2d.pisces.Stroker.close(Stroker.java:592)
  at 
sun.java2d.pisces.PiscesRenderingEngine.pathTo(PiscesRenderingEngine.java:248)
  at 
sun.java2d.pisces.PiscesRenderingEngine.strokeTo(PiscesRenderingEngine.java:231)
  at 
sun.java2d.pisces.PiscesRenderingEngine.strokeTo(PiscesRenderingEngine.java:181)
  at 
sun.java2d.pisces.PiscesRenderingEngine.strokeTo(PiscesRenderingEngine.java:145)
  at sun.java2d.pipe.LoopPipe.getStrokeSpans(LoopPipe.java:274)
  at sun.java2d.x11.X11Renderer.draw(X11Renderer.java:343)
  at sun.java2d.pipe.ValidatePipe.draw(ValidatePipe.java:154)
  at sun.java2d.SunGraphics2D.draw(SunGraphics2D.java:2392)
  at JGears2.renderShape(JGears2.java:244)
  [...]

Attached is the workaround that I checked into IcedTea to make this work
reliably:

2008-11-21  Mark Wielaard  <[EMAIL PROTECTED]>

    * patches/icedtea-stroker-finish.patch: New patch.
    * Makefile.am (ICEDTEA_PATCHES): Add new patch.
    * HACKING: Document new patch.

Cheers,

Mark

--- openjdk6/jdk/src/share/classes/sun/java2d/pisces/Stroker.java
+++ openjdk/jdk/src/share/classes/sun/java2d/pisces/Stroker.java
@@ -695,7 +695,7 @@
             long ldx = (long)(px0 - x0);
             long ldy = (long)(py0 - y0);
             long llen = lineLength(ldx, ldy);
-            long s = (long)lineWidth2*65536/llen;
+            long s = (llen == 0) ? 0 : (long)lineWidth2*65536/llen;
 
             int capx = x0 - (int)(ldx*s >> 16);
             int capy = y0 - (int)(ldy*s >> 16);
@@ -717,7 +717,7 @@
             long ldx = (long)(sx1 - sx0);
             long ldy = (long)(sy1 - sy0);
             long llen = lineLength(ldx, ldy);
-            long s = (long)lineWidth2*65536/llen;
+            long s = (llen == 0) ? 0 : (long)lineWidth2*65536/llen;
 
             int capx = sx0 - (int)(ldx*s >> 16);
             int capy = sy0 - (int)(ldy*s >> 16);