//! Graphics state for the TrueType interpreter.
use super::{
round::RoundState,
zone::{Zone, ZonePointer},
F26Dot6, HintingMode, Point,
};
use core::ops::{Deref, DerefMut};
/// Describes the axis to which a measurement or point movement operation
/// applies.
#[derive(Copy, Clone, PartialEq, Eq, Default, Debug)]
pub enum CoordAxis {
#[default]
Both,
X,
Y,
}
/// Context in which instructions are executed.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html>
#[derive(Debug)]
pub struct GraphicsState<'a> {
/// Fields of the graphics state that persist between calls to the interpreter.
pub retained: RetainedGraphicsState,
/// A unit vector whose direction establishes an axis along which
/// distances are measured.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#projection%20vector>
pub proj_vector: Point<i32>,
/// Current axis for the projection vector.
pub proj_axis: CoordAxis,
/// A second projection vector set to a line defined by the original
/// outline location of two points. The dual projection vector is used
/// when it is necessary to measure distances from the scaled outline
/// before any instructions were executed.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#dual%20projection%20vector>
pub dual_proj_vector: Point<i32>,
/// Current axis for the dual projection vector.
pub dual_proj_axis: CoordAxis,
/// A unit vector that establishes an axis along which points can move.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#freedom%20vector>
pub freedom_vector: Point<i32>,
/// Current axis for point movement.
pub freedom_axis: CoordAxis,
/// Dot product of freedom and projection vectors.
pub fdotp: i32,
/// Determines the manner in which values are rounded.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#round%20state>
pub round_state: RoundState,
/// First reference point.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#rp0>
pub rp0: usize,
/// Second reference point.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#rp1>
pub rp1: usize,
/// Third reference point.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#rp1>
pub rp2: usize,
/// Makes it possible to repeat certain instructions a designated number of
/// times. The default value of one assures that unless the value of loop
/// is altered, these instructions will execute one time.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#loop>
pub loop_counter: u32,
/// First zone pointer.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#zp0>
pub zp0: ZonePointer,
/// Second zone pointer.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#zp1>
pub zp1: ZonePointer,
/// Third zone pointer.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#zp2>
pub zp2: ZonePointer,
/// Outline data for each zone.
///
/// This array contains the twilight and glyph zones, in that order.
pub zones: [Zone<'a>; 2],
/// True if the current glyph is a composite.
pub is_composite: bool,
/// If true, enables a set of backward compatibility heuristics that
/// prevent certain modifications to the outline. The purpose is to
/// support "modern" vertical only hinting that attempts to preserve
/// outline shape and metrics in the horizontal direction. This is
/// enabled by default, but fonts (and specific glyphs) can opt out
/// of this behavior using the INSTCTRL instruction. In practice,
/// opting out is usually only done by "ClearType native" fonts.
///
/// See <https://learn.microsoft.com/en-us/typography/cleartype/truetypecleartype>
/// for more background and some gory details.
///
/// Defaults to true.
///
/// See <https://gitlab.freedesktop.org/freetype/freetype/-/blob/57617782464411201ce7bbc93b086c1b4d7d84a5/src/truetype/ttinterp.h#L344>
pub backward_compatibility: bool,
/// If true, enables more strict error checking.
///
/// Defaults to false.
///
/// See <https://gitlab.freedesktop.org/freetype/freetype/-/blob/57617782464411201ce7bbc93b086c1b4d7d84a5/src/truetype/ttinterp.h#L195>
pub is_pedantic: bool,
/// Set to true when IUP has been executed in the horizontal direction.
pub did_iup_x: bool,
/// Set to true when IUP has been executed in the vertical direction.
pub did_iup_y: bool,
}
impl<'a> GraphicsState<'a> {
/// Returns the factor for scaling unscaled points to pixels.
///
/// For composite glyphs, "unscaled" points are already scaled so we
/// return the identity.
pub fn unscaled_to_pixels(&self) -> i32 {
if self.is_composite {
1 << 16
} else {
self.scale
}
}
/// Resets the non-retained portions of the graphics state.
pub fn reset(&mut self) {
let GraphicsState {
retained,
zones,
is_composite,
..
} = core::mem::take(self);
*self = GraphicsState {
retained,
zones,
is_composite,
..Default::default()
};
self.update_projection_state();
}
/// Resets the retained portion of the graphics state to default
/// values while saving the user instance settings.
pub fn reset_retained(&mut self) {
let scale = self.scale;
let ppem = self.ppem;
let mode = self.mode;
self.retained = RetainedGraphicsState {
scale,
ppem,
mode,
..Default::default()
}
}
}
impl Default for GraphicsState<'_> {
fn default() -> Self {
// For table of default values, see <https://learn.microsoft.com/en-us/typography/opentype/spec/tt_graphics_state>
// All vectors are set to the x-axis (normalized in 2.14)
let vector = Point::new(0x4000, 0);
Self {
retained: RetainedGraphicsState::default(),
proj_vector: vector,
proj_axis: CoordAxis::Both,
dual_proj_vector: vector,
dual_proj_axis: CoordAxis::Both,
freedom_vector: vector,
freedom_axis: CoordAxis::Both,
fdotp: 0x4000,
round_state: RoundState::default(),
rp0: 0,
rp1: 0,
rp2: 0,
loop_counter: 1,
zp0: ZonePointer::default(),
zp1: ZonePointer::default(),
zp2: ZonePointer::default(),
zones: [Zone::default(), Zone::default()],
is_composite: false,
backward_compatibility: true,
is_pedantic: false,
did_iup_x: false,
did_iup_y: false,
}
}
}
/// The persistent graphics state.
///
/// Some of the graphics state is set by the control value program and
/// persists between runs of the interpreter. This struct captures that
/// state.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html>
#[derive(Copy, Clone, Debug)]
pub struct RetainedGraphicsState {
/// Controls whether the sign of control value table entries will be
/// changed to match the sign of the actual distance measurement with
/// which it is compared.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#auto%20flip>
pub auto_flip: bool,
/// Limits the regularizing effects of control value table entries to
/// cases where the difference between the table value and the measurement
/// taken from the original outline is sufficiently small.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#control_value_cut-in>
pub control_value_cutin: F26Dot6,
/// Establishes the base value used to calculate the range of point sizes
/// to which a given DELTAC[] or DELTAP[] instruction will apply.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#delta%20base>
pub delta_base: u16,
/// Determines the range of movement and smallest magnitude of movement
/// (the step) in a DELTAC[] or DELTAP[] instruction.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#delta%20shift>
pub delta_shift: u16,
/// Makes it possible to turn off instructions under some circumstances.
/// When set to TRUE, no instructions will be executed
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#instruct%20control>
pub instruct_control: u8,
/// Establishes the smallest possible value to which a distance will be
/// rounded.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#minimum%20distance>
pub min_distance: F26Dot6,
/// Determines whether the interpreter will activate dropout control for
/// the current glyph.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#scan%20control>
pub scan_control: bool,
/// Type associated with `scan_control`.
pub scan_type: i32,
/// The distance difference below which the interpreter will replace a
/// CVT distance or an actual distance in favor of the single width value.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#single_width_cut_in>
pub single_width_cutin: F26Dot6,
/// The value used in place of the control value table distance or the
/// actual distance value when the difference between that distance and
/// the single width value is less than the single width cut-in.
///
/// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#single_width_value>
pub single_width: F26Dot6,
/// The user requested hinting mode.
pub mode: HintingMode,
/// The scale factor for the current instance. Conversion from font units
/// to 26.6 for current ppem.
pub scale: i32,
/// The nominal pixels per em value for the current instance.
pub ppem: i32,
/// True if a rotation is being applied.
pub is_rotated: bool,
/// True if a non-uniform scale is being applied.
pub is_stretched: bool,
}
impl RetainedGraphicsState {
pub fn new(scale: i32, ppem: i32, mode: HintingMode) -> Self {
Self {
scale,
ppem,
mode,
..Default::default()
}
}
}
impl Default for RetainedGraphicsState {
fn default() -> Self {
// For table of default values, see <https://learn.microsoft.com/en-us/typography/opentype/spec/tt_graphics_state>
Self {
auto_flip: true,
// 17/16 pixels in 26.6
// (17 * 64 / 16) = 68
control_value_cutin: F26Dot6::from_bits(68),
delta_base: 9,
delta_shift: 3,
instruct_control: 0,
// 1 pixel in 26.6
min_distance: F26Dot6::from_bits(64),
scan_control: false,
scan_type: 0,
single_width_cutin: F26Dot6::ZERO,
single_width: F26Dot6::ZERO,
mode: Default::default(),
scale: 0,
ppem: 0,
is_rotated: false,
is_stretched: false,
}
}
}
impl Deref for GraphicsState<'_> {
type Target = RetainedGraphicsState;
fn deref(&self) -> &Self::Target {
&self.retained
}
}
impl DerefMut for GraphicsState<'_> {
fn deref_mut(&mut self) -> &mut Self::Target {
&mut self.retained
}
}
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