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1. Adrian Cochrane (alcinnz@floss.social)'s status on Tuesday, 21-Feb-2023 03:52:18 JST Adrian Cochrane

   FreeType's core logic to compute a signed-distance-field for a vector outline *with overlaps*, after additional validation & initialization, involves counting contours, allocating sidetables to store auxiliary info based on that count, iterate over the contours carefully geometrically decomposing the path & tracing the outline into the output bitmap, iterates again over all pixels tested against all contours to fill in their values, & cleans up.

   1/3?

   • Adrian Cochrane (alcinnz@floss.social)'s status on Tuesday, 21-Feb-2023 04:10:00 JST Adrian Cochrane

     in reply to

     If there's no overlaps to consider only a fraction of that work needs to be done. Namely what I phrased as "decomposing the path & tracing the outline into the output bitmap", without need for its outerloop.

     This is split into substeps: splitting the shape & generating the bounding box.

     There's some legacy functions that are commented due to memory issues.

     The vast majority of the code goes into efficiently computing different tweening functions. There's also debugging functions.

     2/4?

   • Adrian Cochrane (alcinnz@floss.social)'s status on Tuesday, 21-Feb-2023 04:12:12 JST Adrian Cochrane

     in reply to

     Generating the bounding-box, after initialization & validation, involves iterating over the contours & their edges. Foreach it computes a bounding box whose pixels it iterates over, to compute edge distances according to a choice of (often nontrivial) tweening functions & squareroots them. A final pixel iteration fills in missing values. Literal corner-cases are handled specially.

     Splitting a shape involves iterating over a contour & their edges handling each edge-type differently.

     3/3.5?

   • Adrian Cochrane (alcinnz@floss.social)'s status on Tuesday, 21-Feb-2023 04:21:39 JST Adrian Cochrane

     in reply to

     Lines are cloned. Conics are recursively subdivided based on a computed split-point, or allocating two new edges in the base-case. As for cubics, ofcourse computing splitpoints differently.

     Results are collected into a new contour.

     P.S. The mainloop for handling overlaps contour orientation is taken into account, so there's a function to compute that.

     P.P.S. The bounding-box computation differs based on edgetype.

     P.P.P.S. There's a method table to interpret paths.

     4/4 Fin for FreeType SDF!