The AccelGlyphCache code used by the D3D and OGL pipelines is very basic and
currently only holds glyph images whose dimensions are no more than 16 pixels in
either direction. This means that any glyph larger than 16x16 pixels is not
cached and is rendered through a less efficient code path. We should investigate
using a more sophisticated caching and texture packing algorithm to improve
performance of rendering large glyphs.