The following patches are included:
## J2D: Rewrite text rendering
This patch rewrites text rendering for `J2D::DrawString` to now construct
a texture atlas for all ASCII-range glyphs in the FT font face, instead
of constructing a texture for every glyph.
This improves text rendering performance for several reasons:
1. Binding textures is relatively expensive as the GPU is required to do
a context switch for internal data like texture parameters, and also
cannot optimize for accesses to the same texture across draw calls.
This patch removes the need to call `glBindTexture` more than once per
call to `J2D::DrawString`.
2. As a consequence of the above, all glyphs for a given string can now
be rendered in a single call to `glDrawArrays`. This is done by storing
the cached texture coordinates on `CachedGlyph` and constructing a full
array of vertices and texture coordinates for the entire string at
once, resulting in only /one/ set of client-to-device attribute
uploads and only one draw call, instead of being required to upload
attribute data for each glyph separately.
## FontCache: Use map for efficient glyph lookup
This patch updates `CachedFont` to now use an `std::map` for cached glyphs,
instead of an `std::vector`. `std::map` allows O(log n) lookup, whereas
`std::vector` only allows O(n) lookup.
Note: `std::unordered_map` technically has better lookup complexity here,
with amortized O(1) lookup. However, hashmaps have a higher inherent
overhead than red-black trees so this would only be viable when going
above around 1000 entries, which should never happen here for ASCII
glyphs.
Co-authored-by: Ori Sky Farrell <ori.sky.farrell+git@gmail.com>
Reviewed-on: #23
Co-authored-by: ori_sky <redacted@ori.mx>
Co-committed-by: ori_sky <redacted@ori.mx>
