Enum FontColorTransferFunction 

pub enum FontColorTransferFunction {
    Off,
    Gamma(f32),
    TwoCoverageMinusCoverageSq,
}

How to convert font coverage values into alpha and color values.

epaint stores all glyphs in the font atlas as white (with varying opacity), so that egui can reuse the same glyph for different text colors (with a simple color multiplication in the shader).

Because of this simplification, we need to apply a non-linear ramp to the glyph colors before writing them into the font atlas, as a way to compensate.

This whole thing is less than rigorous.

It would be better to either render all text colors into the font atlas (which would require more atlas space, but would allow for more accurate rendering of colored text and emojis), or do the color compensation in the shader, based on the active text color.

When experimenting, use https://fonts.google.com/specimen/Ubuntu to compare to a ground truth.

See https://hikogui.org/2022/10/24/the-trouble-with-anti-aliasing.html for related analysis.

Variants

Off

Use the raw RGBA values from the font rasterizer, without any conversion.

This is the required mode for colored emojis etc.

This mode looks good for black-on-white text, i.e. light mode.

Gamma(f32)

alpha = coverage^gamma.

Gamma=1 looks good for black-on-white text, i.e. light mode.

TwoCoverageMinusCoverageSq

alpha = 2 * coverage - coverage^2

This looks good for white-on-black text, i.e. dark mode.

Very similar to a gamma of 0.5, but produces sharper text. See https://www.desmos.com/calculator/w0ndf5blmn for a comparison to gamma=0.5.

Implementations

impl FontColorTransferFunction

pub const LIGHT_MODE_DEFAULT: Self = Self::Off

A good-looking default for light mode (black-on-white text).

pub const DARK_MODE_DEFAULT: Self = Self::TwoCoverageMinusCoverageSq

A good-looking default for dark mode (white-on-black text).

pub fn to_atlas_color(self, input_color: Color32) -> Color32

How to convert a white color written by the font rasterizer into a color to be written into the font atlas.

pub fn alpha_from_coverage(self, coverage: f32) -> f32

Convert coverage to alpha.

pub fn color_from_coverage(self, coverage: f32) -> Color32

pub fn to_gamma(self) -> f32

Convert this into the closest gamma exponent

Trait Implementations

impl Clone for FontColorTransferFunction

fn clone(&self) -> FontColorTransferFunction

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for FontColorTransferFunction

impl Debug for FontColorTransferFunction

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for FontColorTransferFunction

fn default() -> FontColorTransferFunction

Returns the “default value” for a type.

impl PartialEq for FontColorTransferFunction

fn eq(&self, other: &FontColorTransferFunction) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for FontColorTransferFunction