Text Rendering / Clarity: Implement correct gamma correction

[bryphe]

Issue: The font rendering is not as clear as it could be on low-dpi displays.

One contributing factor is that we are not appropriately handling gamma color space. When we render a glyph, freetype gives us back an alpha mask - each pixel is an 8bit value describing the coverage. If a pixel is 50% covered, it is made 50% black.

However, that 50% does not actually translate to 50% brightness - we treat '128' as the halfway point (which it is in linear space), however, in actuality, ~'186' is the halfway point for brightness.

This is described in more detail here:

• https://www.freetype.org/freetype2/docs/text-rendering-general.html

One open question is - does this mean we can't render text with a transparent background? It might be that, for subpixel rendering and for this, we'd need to render text with a solid background (or a known color / map in the background).

Following from the above document, there might be a way to gamma-correct properly w/o knowing the background: https://bel.fi/alankila/lcd/

The goal of this work would be to implement proper gamma-correction - ideally preserving transparent backgrounds for the text, if possible!

[bryphe]

Another good article on gamma correction: https://learnopengl.com/Advanced-Lighting/Gamma-Correction