I have a few suggestions how to improve the PDFGraphics2D class to be more 
conforming to the java.awt.Graphics2D interface.

I use the FOP library for direct generation of PDF from a Java application 
(i.e. I do not use FOP for XML to PDF translation), but I think that the 
suggestions might be relevant to the FO processing as well.

I found the following problems in the class implementation:

1) When rendering text, the class uses Font.getSize instead of Font.getSize2D. 
This means that the text scales only with integer resolution, which results in 
big errors when rendering text with non-integer size.

2) Text rendering ignores Font's transformation matrix. The matrix is useful 
e.g. for generating slanted or narrowed/widened text. Enabling it is very easy 
(see below).

3) For some reason, drawImage(Image, int, int, ImageObserver) translates the 
white opaque pixels to transparent. I suggest not to set white color as 
transparent, but to change fully transparent pixels to some less usual color 
(I used 255,255,254), and setting this color as transparent.

4) I also changed the text rendering to automatically convert texts 
containing "unsupported chars" (chars that do not display in PDF correctly 
using default fonts) to curves. But this issue you probably solve elsewhere.

It would be also nice to have the PDFGraphics2D.currentStream field protected, 
so that I can fix these problems by subclassing the PDFGraphics2D and override 
the problematic methods instead of rebuilding the original FOP jar file.

Below see the commented diff of the PDFGraphics2D.java file (# precedes 
comments added to the diff) The diffis made against fop-0.20.5 source 
distribution. (unfortunately the line numbers may be slightly incorrect as I 
reformated the source code)

The diff:
----------------------------------------------------------------
71a72
> import java.awt.font.GlyphVector;
148c149
<     protected int currentFontSize;
---
>     protected float currentFontSize;

# in public boolean drawImage(Image, int, int, ImageObserver)

# change fully transparent pixels (alpha = 0) to (255,255,254)
360c361,365
<                         if (alpha != 255) {
---
>                         if (alpha == 0) {
>                             result[count++] = (byte) (0xFF);
>                             result[count++] = (byte) (0xFF);
>                             result[count++] = (byte) (0xFE);
>                         } else if (alpha != 255) {

# in class TempImage

#change transparent color to our special color
429c434
<         PDFColor transparent = new PDFColor(255, 255, 255);
---
>         PDFColor transparent = new PDFColor(255, 255, 254);

# a method that draws text as curves
923a929,933
>     private void drawStringAsGlyphs(String s, float x, float y) {
>         GlyphVector gv = getFont().createGlyphVector(getFontRenderContext(), 
s);
>         fill(gv.getOutline(x, y));
>     }
> 

# in public void drawString(String, float, float)

# draw unsupported text as string
949c959,962
<         // System.out.println("drawString(String)");
---
>         if (!isSupportedString(s)) {
>             drawStringAsGlyphs(s, x, y);
>             return;
>         }

# save font's transform
950a964
>         AffineTransform fontTransform = null;
952a967
>             fontTransform = gFont.getTransform();

#use fractional height instead of integer height
957c972
<             int siz = gFont.getSize();
---
>             float siz = gFont.getSize2D();
962c977
<                         weight, siz * 1000, 0);
---
>                         weight, (int) (siz * 1000 + 0.5), 0);
971c986
<         int size;
---
>         float size;
973c988
<         size = fontState.getFontSize() / 1000;
---
>         size = fontState.getFontSize() / 1000f;

# apply font transform if neccessary
1019a1035,1037
>         if (fontTransform != null && !fontTransform.isIdentity())
>             trans.concatenate(fontTransform);
> 

# new helper methods determining whether string is "supported"

1070a1089,1115
>     private boolean isSupportedString(String s) {
>         for (int i = 0; i < s.length(); ++i)
>             if (!isSupportedChar(s.charAt(i)))
>                 return false;
>         return true;
>     }
> 
>     private boolean isSupportedChar(char c) {
>         if (c >= 0x20 && c < 0xFF)
>             return true;
>         return ("\u20AC\u201A\u0192\u201E\u2026\u2020\u2021\u02C6\u2030
\u0160"
>                 + "\u2039\u004F\u017D\u2018\u2019\u201C\u201D\u2022\u2013
\u2014"
>                 + "\u02DC\u2122\u0161\u203A\u006F\u017E\u0178\u00A1\u00A2
\u00A3"
>                 + "\u00A4\u00A5\u00A6\u00A7\u00A8\u00A9
\u00AA\u00AB\u00AC\u002D"
>                 + "\u00AE\u00AF\u00B0\u00B1\u00B2\u00B3\u00B4\u03BC\u00B6
\u00B7"
>                 + "\u00B8\u00B9\u00BA\u00BB\u00BC\u00BD\u00BE\u00BF\u00C0
\u00C1"
>                 + "\u00C2\u00C3\u00C4\u00C5\u00C6\u00C7\u00C8\u00C9
\u00CA\u00CB"
>                 + "\u00CC\u00CD\u00CE\u00CF\u00D0\u00D1\u00D2\u00D3\u00D4
\u00D5"
>                 + "\u00D6\u00D7\u00D8\u00D9
\u00DA\u00DB\u00DC\u00DD\u00DE\u00DF"
>                 + "\u00E0\u00E1\u00E2\u00E3\u00E4\u00E5\u00E6\u00E7\u00E8
\u00E9"
>                 + "\u00EA\u00EB\u00EC\u00ED\u00EE\u00EF\u00F0\u00F1\u00F2
\u00F3"
>                 + "\u00F4\u00F5\u00F6\u00F7\u00F8\u00F9
\u00FA\u00FB\u00FC\u00FD"
>                 + "\u00FE\u00FF\u004F\u006F\u0160\u0161\u0178
\u017D\u017E\u0192"
>                 + "\u2013\u2014\u2018\u2019\u201A\u201C\u201D\u201E\u2020
\u2021"
>                 + "\u2022\u2026\u2030\u2039\u203A\u20AC\u2122").indexOf(c) !
= -1;
>     }
> 
1367a1413
> 
1371a1418,1425
> 
>         // needed for compiling under jdk1.4
> 
>         public java.awt.image.VolatileImage createCompatibleVolatileImage(
>                 int width, int height, int transparency) {
>             return null;
>         }
>