I've filed RT-37300 for this:



On 5/27/14 3:54 PM, Jim Graham wrote:
Hi Tom,

There are 2 upgrades to consider.  One involves new API, but is probably
best in the long run.

Without API, we'd have to detect if the path were rectangular in the
processing of the CLIP command in NGCanvas.java.  If the 4 coordinates
are an axis aligned rectangle on integer coordinates then we could
special case that with g.setClipRect().  There are other considerations,
such as:

- If there is already a soft non-rect clip, then it should probably not
bother with the special case since it won't simplify anything.
- If we have special cased the rectangle, then we must track that across
save/restore properly.
- If we have a special case cliprect and then we get a non-special case
rect as the argument of a CLIP command, then we need to resolve it into
a singular case (most likely default back to soft clipping).
- The processing that tries to detect "are they clearing the entire
buffer" needs to be aware of any clip in effect - those tests are done
at the javafx.scene.canvas.GraphicsContext level.

We could put that fix in with no new API so it could go in as soon as we
are satisfied with its stability.

If we want to add new API, so that you don't have to construct a path
every time you want to do clipRect() and we don't have to decipher your
path to figure out that it is a rectangle, then we would have to wait
for the next opportunity to add API (FX can add API in between major JDK
releases, but there is a process to go through and I don't think we can
do it for 8u20 any more).  The process for that would be:

javafx.scene.canvas.GraphicsContext would need a new method that would
take the rectangular clipping parameters and put them into the buffer.
The existing fillRect() method would provide a good template.  A new
"command code constant" would have to be added to represent "This is a
clip rectangle request".

NGCanvas would then need to digest the new buffer commands and I believe
that the existing Prism call g.setClipRect() would work to enable the
scissor clip (fast rectangular clipping).

The question is what is the proper API?  If we have it take doubles,
would that imply to developers that there would be soft clipping of the
edges similar to if you used a rectangular path and clip()?  Right now
Node.setClipNode(Rectangle) will do the fast scissor clip
(g.setClipRect()) if the coordinates fall on integer axis-aligned
coordinates, but it will do soft-edged clipping if there is
rotation/skewing, or the coordinates are not integers.  That would
probably be the best API to mimic since HTML5 doesn't have a similar
"cliprect" method...


On 5/27/14 2:57 PM, Tom Schindl wrote:
Is there anything I could do to help getting rectangular clipping into
JavaFX - I tried to find my way through the sources but I'm not sure I
have enough knowledge to provide a patch in this area.

BTW it looks like I'm not alone with the clipping performance problem


On 27.05.14 23:47, Jim Graham wrote:
Canvas is, essentially, a "draw pixels" mechanism.  We have to bundle
the requests into a command stream due to threading issues, but when the
requests get to the render thread then they get turned into pixels so
the command stream is a temporary intermediary.  Some of the hw J2D
pipelines also have a temporary command stream due to platform threading
issues as well.  It all depends on which pipeline you use and on which
platform in the case of J2D.  FX simply normalized the threading on all
pipelines/platforms so that we have a separate UI and render thread in
all cases, but that concept is not foreign to J2D either.

I'm fairly certain that the lack of simple rectangular clipping is
probably the biggest cause of your performance problems.  We do AA on
everything in FX, though, whereas rendering to a BufferedImage by
default will be non-AA unless you requested AA using the graphics hints.
  But on the up-side, we hw accelerate just about every operation in FX
so it should be on par with performance there, modulo the lack of
rectangular clipping...


On 5/23/14 5:46 PM, Tom Schindl wrote:

As an experiment I've now written a SWT-GC implementation using a
BufferedImage & Graphics2D and transfering the pixels over to JavaFX
the performance is as it is with native SWT.

I always thought Canvas works similar to Image and one only draws
- looks like that is not the case, having a dep in my application
java.awt is not what I'm aiming at but without acceptable
performance in
conjunction with clipping it looks like i have to go this route :-(


On 23.05.14 23:57, Tom Schindl wrote:
In the current usecase it is a rect all time but that's just in this
special use case.

I guess that rect clipping is the most common one so having an
optimization for rects and a slow path for none rects might help.


Von meinem iPhone gesendet

Am 23.05.2014 um 23:35 schrieb Jim Graham <james.gra...@oracle.com>:

Are you clipping to an arbitrary path in all cases or just a
rectangle?  Unfortunately we only offer the arbitrary
clip-to-current-path method that isn't optimized for basic
rectangular clipping and it implements soft clipping.

There is an outstanding tweak that we added faster clipping support
for WebNode and we need to start using it for
Node.setClipNode(non-rectangle) and Canvas, but we haven't
implemented that yet.
(https://javafx-jira.kenai.com/browse/RT-30107)  It basically is a
direct "render this texture through that other texture as a clip"
operation instead of the current code that runs it through some
Blend effect filters.  It would definitely improve your run times,
but I'm not sure how much.

Even more savings could be had for rectangular clips if we provided
some way to communicate them to the GC...


On 5/23/14 11:47 AM, Tom Schindl wrote:

Maybe as some of you might know I've been working since sometime on
on JavaFX and to implement direct drawing operations we use

I've today tried to run a heavy direct drawing grid
implementation and
it performed very bad because it makes heavy use of clipping.

For a grid I've counted ~1500 clipping operations the library works
something like this:

boolean activeClip;
Canvas canvas = new Canvas();

public void setClipping(PathIterator pathIterator) {
    GraphicsContext gc = canvas.getGraphicsContext2D();
    if(activeClip) {
      activeClip= false;

    if( pathIterator == null ) {

    activeClip = true;
    float coords[] = new float[6];

         float x = 0;
         float y = 0;

         gc.moveTo(0, 0);

         while( ! pathIterator.isDone() ) {
             switch (pathIterator.currentSegment(coords)) {
             case PathIterator.SEG_CLOSE:
                 gc.lineTo(x, y);
             case PathIterator.SEG_CUBICTO:
                 gc.bezierCurveTo(coords[0], coords[1], coords[2],
coords[4], coords[5]);
             case PathIterator.SEG_LINETO:
                 gc.lineTo(coords[0], coords[1]);
             case PathIterator.SEG_MOVETO:
                 gc.moveTo(coords[0], coords[1]);
                 x = coords[0];
                 y = coords[1];
             case PathIterator.SEG_QUADTO:
                 gc.quadraticCurveTo(coords[0], coords[1],
coords[2], coords[3]);


Am I doing something ultimately wrong, totally wrong? Has anyone an
how I would work around the problem?


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