Regarding rasterizing glyphs from a font, FreeType is hooked up to Splash's path-building methods.
There's "Pattern" subclasses for computing the colour at a given pixel.
There's a linked stack of drawing state, closely resembling the one Poppler reimplemented for itself.
There's a scanline algorithm implemented for intersecting geometries, thus implementing clipping, as managed by a seperate class. Taking shortcuts for rectangles.
alcinnz