//! Rounding state.
use super::{super::F26Dot6, graphics::GraphicsState};
/// Rounding strategies supported by the interpreter.
#[derive(Copy, Clone, PartialEq, Eq, Default, Debug)]
pub enum RoundMode {
/// Distances are rounded to the closest grid line.
///
/// Set by `RTG` instruction.
#[default]
Grid,
/// Distances are rounded to the nearest half grid line.
///
/// Set by `RTHG` instruction.
HalfGrid,
/// Distances are rounded to the closest half or integer pixel.
///
/// Set by `RTDG` instruction.
DoubleGrid,
/// Distances are rounded down to the closest integer grid line.
///
/// Set by `RDTG` instruction.
DownToGrid,
/// Distances are rounded up to the closest integer pixel boundary.
///
/// Set by `RUTG` instruction.
UpToGrid,
/// Rounding is turned off.
///
/// Set by `ROFF` instruction.
Off,
/// Allows fine control over the effects of the round state variable by
/// allowing you to set the values of three components of the round_state:
/// period, phase, and threshold.
///
/// More formally, maps the domain of 26.6 fixed point numbers into a set
/// of discrete values that are separated by equal distances.
///
/// Set by `SROUND` instruction.
Super,
/// Analogous to `Super`. The grid period is sqrt(2)/2 pixels rather than 1
/// pixel. It is useful for measuring at a 45 degree angle with the
/// coordinate axes.
///
/// Set by `S45ROUND` instruction.
Super45,
}
/// Graphics state that controls rounding.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#round%20state>
#[derive(Copy, Clone, Debug)]
pub struct RoundState {
pub mode: RoundMode,
pub threshold: i32,
pub phase: i32,
pub period: i32,
}
impl Default for RoundState {
fn default() -> Self {
Self {
mode: RoundMode::Grid,
threshold: 0,
phase: 0,
period: 64,
}
}
}
impl RoundState {
pub fn round(&self, distance: F26Dot6) -> F26Dot6 {
use super::math;
use RoundMode::*;
let distance = distance.to_bits();
let result = match self.mode {
// <https://gitlab.freedesktop.org/freetype/freetype/-/blob/57617782464411201ce7bbc93b086c1b4d7d84a5/src/truetype/ttinterp.c#L1958>
HalfGrid => {
if distance >= 0 {
(math::floor(distance) + 32).max(0)
} else {
(-(math::floor(-distance) + 32)).min(0)
}
}
// <https://gitlab.freedesktop.org/freetype/freetype/-/blob/57617782464411201ce7bbc93b086c1b4d7d84a5/src/truetype/ttinterp.c#L1913>
Grid => {
if distance >= 0 {
math::round(distance).max(0)
} else {
(-math::round(-distance)).min(0)
}
}
// <https://gitlab.freedesktop.org/freetype/freetype/-/blob/57617782464411201ce7bbc93b086c1b4d7d84a5/src/truetype/ttinterp.c#L2094>
DoubleGrid => {
if distance >= 0 {
math::round_pad(distance, 32).max(0)
} else {
(-math::round_pad(-distance, 32)).min(0)
}
}
// <https://gitlab.freedesktop.org/freetype/freetype/-/blob/57617782464411201ce7bbc93b086c1b4d7d84a5/src/truetype/ttinterp.c#L2005>
DownToGrid => {
if distance >= 0 {
math::floor(distance).max(0)
} else {
(-math::floor(-distance)).min(0)
}
}
// <https://gitlab.freedesktop.org/freetype/freetype/-/blob/57617782464411201ce7bbc93b086c1b4d7d84a5/src/truetype/ttinterp.c#L2049>
UpToGrid => {
if distance >= 0 {
math::ceil(distance).max(0)
} else {
(-math::ceil(-distance)).min(0)
}
}
// <https://gitlab.freedesktop.org/freetype/freetype/-/blob/57617782464411201ce7bbc93b086c1b4d7d84a5/src/truetype/ttinterp.c#L2145>
Super => {
if distance >= 0 {
let val =
((distance + (self.threshold - self.phase)) & -self.period) + self.phase;
if val < 0 {
self.phase
} else {
val
}
} else {
let val =
-(((self.threshold - self.phase) - distance) & -self.period) - self.phase;
if val > 0 {
-self.phase
} else {
val
}
}
}
// <https://gitlab.freedesktop.org/freetype/freetype/-/blob/57617782464411201ce7bbc93b086c1b4d7d84a5/src/truetype/ttinterp.c#L2199>
Super45 => {
if distance >= 0 {
let val = (((distance + (self.threshold - self.phase)) / self.period)
* self.period)
+ self.phase;
if val < 0 {
self.phase
} else {
val
}
} else {
let val = -((((self.threshold - self.phase) - distance) / self.period)
* self.period)
- self.phase;
if val > 0 {
-self.phase
} else {
val
}
}
}
// <https://gitlab.freedesktop.org/freetype/freetype/-/blob/57617782464411201ce7bbc93b086c1b4d7d84a5/src/truetype/ttinterp.c#L1870>
Off => distance,
};
F26Dot6::from_bits(result)
}
}
impl GraphicsState<'_> {
pub fn round(&self, distance: F26Dot6) -> F26Dot6 {
self.round_state.round(distance)
}
}
#[cfg(test)]
mod tests {
use super::{F26Dot6, RoundMode, RoundState};
#[test]
fn round_to_grid() {
round_cases(
RoundMode::Grid,
&[(0, 0), (32, 64), (-32, -64), (64, 64), (50, 64)],
);
}
#[test]
fn round_to_half_grid() {
round_cases(
RoundMode::HalfGrid,
&[(0, 32), (32, 32), (-32, -32), (64, 96), (50, 32)],
);
}
#[test]
fn round_to_double_grid() {
round_cases(
RoundMode::DoubleGrid,
&[(0, 0), (32, 32), (-32, -32), (64, 64), (50, 64)],
);
}
#[test]
fn round_down_to_grid() {
round_cases(
RoundMode::DownToGrid,
&[(0, 0), (32, 0), (-32, 0), (64, 64), (50, 0)],
);
}
#[test]
fn round_up_to_grid() {
round_cases(
RoundMode::UpToGrid,
&[(0, 0), (32, 64), (-32, -64), (64, 64), (50, 64)],
);
}
#[test]
fn round_off() {
round_cases(
RoundMode::Off,
&[(0, 0), (32, 32), (-32, -32), (64, 64), (50, 50)],
);
}
fn round_cases(mode: RoundMode, cases: &[(i32, i32)]) {
for (value, expected) in cases.iter().copied() {
let value = F26Dot6::from_bits(value);
let expected = F26Dot6::from_bits(expected);
let state = RoundState {
mode,
..Default::default()
};
let result = state.round(value);
assert_eq!(
result, expected,
"mismatch in rounding: {mode:?}({value}) = {result} (expected {expected})"
);
}
}
}
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