diff options
Diffstat (limited to 'libass/ass_rasterizer.c')
| -rw-r--r-- | libass/ass_rasterizer.c | 25 |
1 files changed, 23 insertions, 2 deletions
diff --git a/libass/ass_rasterizer.c b/libass/ass_rasterizer.c index bf217a7..05463de 100644 --- a/libass/ass_rasterizer.c +++ b/libass/ass_rasterizer.c @@ -85,6 +85,27 @@ void rasterizer_done(ASS_Rasterizer *rst) } +/* + * Tiled Rasterization Algorithm + * + * 1) Convert splines into polylines using recursive subdivision. + * + * 2) Determine which segments of resulting polylines fall into each tile. + * That's done through recursive splitting of segment array with horizontal or vertical lines. + * Each individual segment can lie fully left(top) or right(bottom) from the splitting line or cross it. + * In the latter case copies of such segment go to both output arrays. Also winding count + * of the top-left corner of the second result rectangle gets calculated simultaneously with splitting. + * Winding count of the first result rectangle is the same as of the source rectangle. + * + * 3) When the splitting is done to the tile level, there are 3 possible outcome: + * - Tile doesn't have segments at all--fill it with solid color in accordance with winding count. + * - Tile have only 1 segment--use simple half-plane filling algorithm. + * - Generic case with 2 or more segments. + * In the latter case each segment gets rasterized as right trapezoid into buffer + * with additive or subtractive blending. + */ + + typedef struct { int32_t x, y; } OutlinePoint; @@ -169,7 +190,7 @@ static inline int add_line(ASS_Rasterizer *rst, OutlinePoint pt0, OutlinePoint p /** * \brief Add quadratic spline to polyline - * Preforms recursive subdivision if necessary. + * Performs recursive subdivision if necessary. */ static int add_quadratic(ASS_Rasterizer *rst, OutlinePoint pt0, OutlinePoint pt1, OutlinePoint pt2) @@ -195,7 +216,7 @@ static int add_quadratic(ASS_Rasterizer *rst, /** * \brief Add cubic spline to polyline - * Preforms recursive subdivision if necessary. + * Performs recursive subdivision if necessary. */ static int add_cubic(ASS_Rasterizer *rst, OutlinePoint pt0, OutlinePoint pt1, OutlinePoint pt2, OutlinePoint pt3) |