The previous implementation is correct but it is too complex.
The revised algorithm is based on the fact that each split moves
the control points closer to the trisection points on the chord.
The corresponding distances are good surrogates for the curve
deviation from the straight line.
This cubic flattening algorithm is somewhat similar to the conic
algorithm based the distance from the control point to the middle of
the chord. The cubic distances, however, decrease less predictably
but are easy enough to calculate on each step.
* src/smooth/ftgrays.c (gray_render_cubic): Replace the split
condition.
* src/raster/ftraster.c [STANDALONE] (FT_Outline_Get_CBox): Add
function.
[!STANDALONE]: Include FT_OUTLINE_H.
(ft_black_render): Compute CBox and reject glyphs larger than
0xFFFF x 0xFFFF.
* src/smooth/ftgrays.c (gray_raster_render): Reject glyphs larger
than 0xFFFF x 0xFFFF.
This monster commit was created by applying Nikhil's scripts
`docconverter.py' and `markify.py' to all C header and source files,
followed up by minor manual clean-up.
No change in functionality, of course.
I used commit f7419907bc6044b9b7057f9789866426c804ba82 from
https://github.com/nikramakrishnan/freetype-docs.git.
The robust rendering of estra large glyphs came with unbearable cost.
The old way of bisecting should fail but fail faster.
* src/smooth/ftgrays.c (gray_convert_glyph): Switch back to bisecting
in y-direction.
*/* [FT_CONFIG_OPTION_PIC]: Remove all code guarded by this
preprocessor symbol.
*/*: Replace `XXX_GET' macros (which could be either a function in
PIC mode or an array in non-PIC mode) with `xxx' arrays.
* include/freetype/internal/ftpic.h, src/autofit/afpic.c,
src/autofit/afpic.h, src/base/basepic.c, src/base/basepic.h,
src/base/ftpic.c, src/cff/cffpic.c, src/cff/cffpic.h,
src/pshinter/pshpic.c, src/pshinter/pshpic.h, src/psnames/pspic.c,
src/psnames/pspic.h, src/raster/rastpic.c, src/raster/rastpic.h,
src/sfnt/sfntpic.c, src/sfnt/sfntpic.h, src/smooth/ftspic.c,
src/smooth/ftspic.h, src/truetype/ttpic.c, src/truetype/ttpic.h:
Removed.
We used to split large glyphs into horizontal bands and continue
bisecting them still horizontally if that was not enough. This is
guaranteed to fail when a single scanline cannot fit into the
rendering memory pool. Now we bisect the bands vertically so that
the smallest unit is a column of the band height, which is guranteed
to fit into memory.
* src/smooth/ftgrays.c (gray_convert_glyph): Implement it.
At large sizes almost but not exactly horizontal segments can quickly
drain the rendering pool. This patch at least avoids filling the pool
with trivial cells. Beyond this, we can only increase the pool size.
Reported, analyzed, and tested by Colin Fahey.
* src/smooth/ftgrays.c (gray_set_cell): Do not record trivial cells.
* src/smooth/ftgrays.c [STANDALONE] (OVERFLOW_ADD_LONG,
OVERFLOW_SUB_LONG, OVERFLOW_MUL_LONG, NEG_LONG): New macros.
[!STANDALONE]: Include FT_INTERNAL_CALC_H.
(gray_render_cubic): Use those macros where appropriate.
We don't need some divisions if a line segments stays within a single
row or a single column of pixels.
* src/smooth/ftgrays.c (gray_render_line) [FT_LONG64]: Make divisions
conditional.
The algorithm calls `gray_set_cell' at the start of each new contour
or when the contours cross the cell boundaries. Double-checking for
that is wasteful.
* src/smooth/ftgrays.c (gray_set_cell): Remove check for a new cell.
(gray_convert_glyph): Remove initialization introduced by 44b172e88.
Alexei Podtelezhnikov