To split a glyph's extent region to three sub-boxes
as below.
left box 2 x h
center box (w-4) x h
right box 2 x h
Take a simple glyph A as an example:
*
__* *__
*****
* *
~~ ~~
The left box and right boxes are both 2 x 2. The center box
is 2 x 4.
The left box has two bitmaps 0001'b and 0010'b to indicate
the real inked area.
The right box also has two bitmaps 0010'b and 0001'b.
And then we can check the inked area in left and right boxes with
previous glyph. If the direction is from left to right, then we
need to check the previous right bitmap with current left bitmap.
And if we found the center box has overlapped or we overlap with
not only the previous glyph, we will treat it as real overlapped
and will render the glyphs via mask.
If we only intersect with previous glyph on the left/right edge.
Then we further compute the real overlapped bits. We set a loose
check criteria here, if it has less than two pixel overlapping, we
treat it as non-overlapping.
With this patch, The aa10text boost fom 1660000 to 320000.
Almost double the performance! And the cairo test result is the
same as without this patch.
Signed-off-by: Zhigang Gong <zhigang.gong@linux.intel.com>
c1bd50d58d