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Diffstat (limited to 'src/sdf/ftsdf.c')
| -rw-r--r-- | src/sdf/ftsdf.c | 77 |
1 files changed, 77 insertions, 0 deletions
diff --git a/src/sdf/ftsdf.c b/src/sdf/ftsdf.c index 29bc0c3ca..1edb00064 100644 --- a/src/sdf/ftsdf.c +++ b/src/sdf/ftsdf.c @@ -9,6 +9,83 @@ /************************************************************************** * + * A brief technical overview of how the SDF rasterizer works + * ---------------------------------------------------------- + * + * [Notes]: + * * SDF stands for Signed Distance Field everywhere. + * + * * This renderer generates SDF directly from outlines. There is + * another renderer called 'bsdf', which converts bitmaps to SDF; see + * file `ftbsdf.c` for more. + * + * * The basic idea of generating the SDF is taken from Viktor Chlumsky's + * research paper. + * + * Chlumsky, Viktor: Shape Decomposition for Multi-channel Distance + * Fields. Master's thesis. Czech Technical University in Prague, + * Faculty of InformationTechnology, 2015. + * + * For more information: https://github.com/Chlumsky/msdfgen + * + * ======================================================================== + * + * Generating SDF from outlines is pretty straightforward. + * + * (1) We have a set of contours that make the outline of a shape/glyph. + * Each contour comprises of several edges, with three types of edges. + * + * * line segments + * * conic Bezier curves + * * cubic Bezier curves + * + * (2) Apart from the outlines we also have a two-dimensional grid, namely + * the bitmap that is used to represent the final SDF data. + * + * (3) In order to generate SDF, our task is to find shortest signed + * distance from each grid point to the outline. The 'signed + * distance' means that if the grid point is filled by any contour + * then its sign is positive, otherwise it is negative. The pseudo + * code is as follows. + * + * ``` + * foreach grid_point (x, y): + * { + * int min_dist = INT_MAX; + * + * foreach contour in outline: + * { + * foreach edge in contour: + * { + * // get shortest distance from point (x, y) to the edge + * d = get_min_dist(x, y, edge); + * + * if (d < min_dist) + * min_dist = d; + * } + * + * bitmap[x, y] = min_dist; + * } + * } + * ``` + * + * (4) After running this algorithm the bitmap contain sinformation about the closest + * point from each point to the outline of the shape. Of course, + * while this is the most straightforward way of generating SDF, we + * use various optimizations in this rasterizer. See the + * `sdf_generate_*' functions in this file for all details. + * + * The optimization currently used by default is subdivision; see + * function `sdf_generate_subdivision` for more. + * + * Also, to see how we compute the shortest distance from a point to + * each type of edge, check out the `get_min_distance_*' functions. + * + */ + + + /************************************************************************** + * * for tracking used memory * */ |