Adrian Cochrane
FreeType includes a smoothing subsystem, exposed as a renderer. To ensure text looks good even on the worst monitors.
It's render method, after validation, computes x & y shifts considering the pixel mode, bitmap position, & maybe origin. This shift, if any, is temporarily applied before checking the mode & cleaning up. For `NORMAL` or `LIGHT` modes it considers specially rendering outline overlaps, or defers to the rasterizer. Otherwise it dynamically determines LCD filters to apply.
1/?
Adrian Cochrane
To smooth outline overlaps (when they're not too big) it configures & defers to the rasterizer with a temporary scale, passing a callback tweaking the run-length rasterizer to avoid numeric overflows.
To preprocess LCD rendering it defers to the rasterizer at scale 3 on appropriate axis. With or without, depending on buildflags, multiple translation transforms.
There's a smoothing initializer, deferring to rasterizer's. Other methods defers to core infrastructure.
2/?
Adrian Cochrane
FreeType's smoother subsystem bundles its own "grays" rasterizer.
Aside from some minimal methods fullfilling the interface...
After validation it's render method consults flags & other parameters to compute the bounding box. Before (after some normalizing) iterating over the Y axis & "bands" therein pairing them up, filling intermediate space, decompose outline (with longjump error-handling & maybe no trace-debugging) & halving the width to validate & incorporating into the next bandpair.
3/
Adrian Cochrane
For each scanline, whether within that loop (& it's inner loop as it creates "cells") or in single-scanline fastpath, Grays checks some fastpaths (which they say happens surprisingly often) before iterating over X axis creating new "cells".
For vertical lines Grays iterates over Y axis adding new "cells".
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Sweeping involves iterating over the inner Y axis & cells therein to appropriately call the span renderer, if it's not filling those bytes itself.
Cells have debug output.
6/6 Fin!
Adrian Cochrane
Splitting cubics involves some adds, halving, quartering, & 8th'ing. Via bitshifts. Though I'm not clear on what geometry on what geometry it's implementing.
Conics works similarly, but with step-count & dx precomputed, & using an innerloop with bittwiddling to split the curve. Ofcourse the split formula is simpler. May use compiler intrinsics for that precomputation, based on build flags.
Upon lines it applies clipping & handles special cases before iterating over Y axis.
5/6!
Adrian Cochrane
That decomposition is configured to call a methodtable defining how to handle moves, lines, conics, & cubics in Grays-specific ways. If compiled stand-alone buildflags use copy-pasted version of `FT_Decompose` to call these with appropriate numeric tweaks.
Move-to scales & sets the coordinates, initiating a new "cell" linkedlist.
Upon cubics it tweaks controlpoints checking shortcuts & repeatedly splits the cubic until it can render as a line & iterate to the next split.
4/5?
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