Re: request for comment on java2d stuff

[graydon hoare]

Sascha Brawer <address@hidden> writes:

> (1) In GdkGraphics2D.walkPath(PathIterator), the treatment of quadratic
> splines is almost, but not entirely correct. The page
> 
>   http://pfaedit.sourceforge.net/bezier.html

great! you know, I actually did dig through pfaedit's source code, but
was too thick-headed to realize clearly what I was seeing. I have now
made this change.

> (2) Strokes that are not a BasicStroke: The drawing methods could
> check whether the value of the stroke field is an instance of
> BasicStroke. If not, they would not directly call into Cairo. For
> example, GdkGraphics2D.draw(Shape) could look as follows:

hm, yes, this is plausible. I will make this change too.

> To increase performance, you could check whether the image is in a
> format that is directly supported by Cairo, such as TYPE_INT_ARGB
> with an sRGB ColorSpace. If this is the case, you could retrieve the
> underlying DataBufferInt (via getRaster().getDataBuffer()) and
> directly pass its int[] to GdkGraphics2D.drawPixels.

ok, easy enough.

> (4) Methods like GdkGraphics2D.drawRenderedImage can be implemented
> by fetching a Raster from the RenderedImage and proceeding as with
> BufferedImage. My proposal would be to define a private drawRaster
> method that gets called by the various public image drawing methods.

ok.

> (5) It might be worth extending the native method
> GdkGraphics2D.drawPixels to include an offset into the int[]. This
> might be useful for cases where pixel (0,0) is not at index 0 of the
> int[] that belongs to the DataBuffer.

ok.

> (6) You could further avoid copying pixel data by slightly changing
> the native implementation of GdkGraphics2D.drawPixels. Instead of
> GetIntArrayElements, I'd recommend using GetPrimitiveArrayCritical
> and ReleasePrimitiveArrayCritical. See
> 
>   http://java.sun.com/j2se/1.4.2/docs/guide/jni/jni-
> 12.html#GetPrimitiveArrayCritical

I would prefer not to do this for now. I can't say for certain that
cairo won't make system calls that other java threads are aware of or
possibly involved in. cairo *does* produce outgoing X traffic,
possibly some traffic which will interact with the traffic the GDK
peer threads are generating / receiving.

> (7) As of how to implement Font.getFamily(java.util.Locale) etc.,
> (you have FIXMEs in that code)

actually the FIXME is from previous authors. I have subsequently
implemented the font model as described by the JDK documentation
(property maps, logical, family and face name, etc.) and this is no
longer a problem.

> Maybe we can use an extended version of this interface for the
> FontPeers that you've proposed in your recent e-mail. (The
> getGlyphName method is not needed for Java2D, but it would be
> necessary if someone wanted to write a decent PostScript or PDF
> provider for javax.print.)

yes, that interface looks like about all I need to support the pango
font backend. perhaps a couple more methods, if I find any. shall I
modify Font to use such a delegate, and place factory methods in
Toolkit? (and shall we settle on the word "delegate" to denote
peer-like things which our extended factory methods will produce?)

-graydon