grafx - Extensible Java Graphics Package Code

Optimzing the flat polygon fill routine for custom pix branch. It's just a
copy and paste, with setPix() modified to setPixCust().

I think I'm done with the fillPolygon() optimization now. Took out the last
branch, which was the check for 'odd'. Jumping ahead on the linked list
instead. It's much more straightforward, and it's equivalent, but may be a bit
less intuitive to read.

Simplifying fillPolygon() by taking out the explicit use of 'even' or 'odd'.
Now it's implicit with the 'node0 = node1.nextEdge'. There is no difference in
the logic. It's equivalent, I checked with my modeling skills.

Gradually simplifying the 2D fillPolygon() as well.

in 2D graphics, simplifying polygon fill a little bit by using 'odd' instead of
'even' in local variable name.

Removing one excessive 'if' branch, which checks that 'xStart < xEnd'. We go
ahead and do the expensive setup computations even if this isn't the case,
because that zero-length scanline for the part of the polygon is rather rare.

Oops, in polygon fill optimization changing nomenclature:
y0 -> z0
y1 -> z1
These were named incorrectly even though the code is the same.

Still simplifying the polygon fill, bit by bit.

Further optimizations in polygon filling, avoiding repeated array lookup.

Adding m_offset to RasterDepthGraphics but as I was incorporating it I realized
that there may be some performance gains to be had in fillPolygon(), the
simplest version of that method.