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[smooth] Sub-banding protocol revision.

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Rasterization sub-banding is utilized at large sizes while using
rather small fixed memory pool. Indeed it is possible to make an
educated guess how much memory is necessary at a given size for a
given glyph. It turns out that, for large majority of European glyphs,
you should store about 8 times more boundary pixels than their height.
Or, vice versa, if your memory pool can hold 800 pixels the band
height should be 100 and you should sub-band anything larger than
that. Should you still run out of memory, FreeType bisects the band
but you have wasted some time. This is what has been implemented in
FreeType since the beginning.

It was overlooked, however, that the top band could grow to twice the
default band size leading to unnecessary memory overflows there. This
commit fixes that. Now the bands are distributed more evenly and
cannot exceed the default size.

Now the magic number 8 is really suitable for rather simple European
scripts. For complex Chinese logograms the magic number should be 13
but that is subject for another day.

* src/smooth/ftgrays.c (gray_convert_glyph): Revise sub-banding
protocol.
This commit is contained in:
Alexei Podtelezhnikov 2016-07-08 00:16:07 -04:00
parent 783cbcd67d
commit 4a2f8f1faf
2 changed files with 39 additions and 11 deletions
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27
ChangeLog
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@ -1,3 +1,30 @@
2016-07-08 Alexei Podtelezhnikov <apodtele@gmail.com>
[smooth] Sub-banding protocol revision.
Rasterization sub-banding is utilized at large sizes while using
rather small fixed memory pool. Indeed it is possible to make an
educated guess how much memory is necessary at a given size for a
given glyph. It turns out that, for large majority of European glyphs,
you should store about 8 times more boundary pixels than their height.
Or, vice versa, if your memory pool can hold 800 pixels the band
height should be 100 and you should sub-band anything larger than
that. Should you still run out of memory, FreeType bisects the band
but you have wasted some time. This is what has been implemented in
FreeType since the beginning.
It was overlooked, however, that the top band could grow to twice the
default band size leading to unnecessary memory overflows there. This
commit fixes that. Now the bands are distributed more evenly and
cannot exceed the default size.
Now the magic number 8 is really suitable for rather simple European
scripts. For complex Chinese logograms the magic number should be 13
but that is subject for another day.
* src/smooth/ftgrays.c (gray_convert_glyph): Revise sub-banding
protocol.
2016-07-07 suzuki toshiya <mpsuzuki@hiroshima-u.ac.jp>
[mac] Fix Savannah bug #48417.

23
src/smooth/ftgrays.c
View File

@ -1893,27 +1893,28 @@ typedef ptrdiff_t FT_PtrDist;
gray_convert_glyph( RAS_ARG )
{
TCell buffer[FT_MAX_GRAY_POOL];
const int band_size = FT_MAX_GRAY_POOL / 8;
gray_TBand bands[32];
gray_TBand* band;
int n, num_bands;
TCoord band_size = FT_MAX_GRAY_POOL / 8;
int num_bands;
TCoord min, max, max_y;
gray_TBand bands[32]; /* enough to accommodate bisections */
gray_TBand* band;
/* set up vertical bands */
num_bands = (int)( ( ras.max_ey - ras.min_ey ) / band_size );
if ( num_bands == 0 )
num_bands = 1;
if ( num_bands >= 39 )
num_bands = 39;
if ( ras.count_ey > band_size )
{
/* two divisions rounded up */
num_bands = (int)( ( ras.count_ey + band_size - 1) / band_size );
band_size = ( ras.count_ey + num_bands - 1 ) / num_bands;
}
min = ras.min_ey;
max_y = ras.max_ey;
for ( n = 0; n < num_bands; n++, min = max )
for (; min < max_y; min = max )
{
max = min + band_size;
if ( n == num_bands - 1 || max > max_y )
if ( max > max_y )
max = max_y;
bands[0].min = min;