diff options
Diffstat (limited to 'src/smooth/ftgrays.c')
| -rw-r--r-- | src/smooth/ftgrays.c | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/src/smooth/ftgrays.c b/src/smooth/ftgrays.c index 8f87f8483..4efc0d083 100644 --- a/src/smooth/ftgrays.c +++ b/src/smooth/ftgrays.c @@ -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. * */ |