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Rendering considerations.

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This commit is contained in:
Alexei Podtelezhnikov 2019-05-20 23:09:59 -04:00
parent b0522701f8
commit 141e3173db
2 changed files with 20 additions and 3 deletions
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9
ChangeLog
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@ -195,6 +195,11 @@
the chord. The cubic distances, however, decrease less predictably
but are easy enough to calculate on each step.
The new algorithm produces slightly larger number of splits, which is
compensated by its simplicity. The overall rendering performance is
improved by 1-2%. The larger number of splits does not necessarily
result in higher quality, which stays comparable.
* src/smooth/ftgrays.c (gray_render_cubic): Replace the split
condition.
@ -209,6 +214,10 @@
Optimize Bézier bisections.
This change makes bisections faster by 20-30%. When inlined into
`gray_render_cubic', this makes the function faster by 10% and is
noticeable in the overall rendering performance.
* src/raster/ftraster.c (Split_Conic, Split_Cubic): Use shifts and
refactor.
* src/smooth/ftgrays.c (gray_split_conic, gray_split_cubic): Ditto.

14
src/smooth/ftgrays.c
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@ -45,7 +45,7 @@
* This is a new anti-aliasing scan-converter for FreeType 2. The
* algorithm used here is _very_ different from the one in the standard
* `ftraster' module. Actually, `ftgrays' computes the _exact_
* coverage of the outline on each pixel cell.
* coverage of the outline on each pixel cell by straight segments.
*
* It is based on ideas that I initially found in Raph Levien's
* excellent LibArt graphics library (see https://www.levien.com/libart
@ -58,6 +58,14 @@
* different way, and I don't use sorted vector paths. Also, it doesn't
* use floating point values.
*
* Bézier segments are flattened by splitting them until their deviation
* from straight line becomes much smaller than a pixel. Therefore, the
* pixel coverage by a Bézier curve is calculated approximately. To
* estimate the deviation, we use the distance from the control point
* to the conic chord centre or the cubic chord trisection. These
* distances vanish fast after each split. In the conic case, they vanish
* predictably and the number of necessary splits can be calculated.
*
* This renderer has the following advantages:
*
* - It doesn't need an intermediate bitmap. Instead, one can supply a
@ -67,7 +75,7 @@
* callback.
*
* - A perfect anti-aliaser, i.e., it computes the _exact_ coverage on
* each pixel cell.
* each pixel cell by straight segments.
*
* - It performs a single pass on the outline (the `standard' FT2
* renderer makes two passes).
@ -75,7 +83,7 @@
* - It can easily be modified to render to _any_ number of gray levels
* cheaply.
*
* - For small (< 20) pixel sizes, it is faster than the standard
* - For small (< 80) pixel sizes, it is faster than the standard
* renderer.
*
*/