extendr_api/graphics/

mod.rs

// ## Resources for Developers
//
// Graphic device is documented in the R-internals. The header file also
// contains the useful information. The code of the graphics package is also useful to
// see what values are used by default (i.e. `GInit`).
//
// - https://cran.r-project.org/doc/manuals/r-devel/R-ints.html
// - https://github.com/wch/r-source/blob/trunk/src/include/R_ext/GraphicsDevice.h
// - https://github.com/wch/r-source/blob/trunk/src/library/graphics/src/graphics.c
//
// While the documents are good, we need to refer to the real implementaions to
// find hints.
//
// - postscript device: https://github.com/wch/r-source/blob/trunk/src/library/grDevices/src/devPS.c
// - svglite package: https://github.com/r-lib/svglite/blob/main/src/devSVG.cpp
// - devout package: https://github.com/coolbutuseless/devout/blob/master/src/rdevice.cpp
//
// For newer features, the blog posts by Paul Murrell might be helpful:
//
// - https://developer.r-project.org/Blog/public/2020/07/15/new-features-in-the-r-graphics-engine/index.html
// - https://developer.r-project.org/Blog/public/2021/12/06/groups-and-paths-and-masks-in-r-graphics/index.html
// - https://developer.r-project.org/Blog/public/2021/12/14/updating-graphics-devices-for-r-4.2.0/index.html

//! Graphic Device Operations
//!
//! ## Control an existing graphic device
//!
//! TODO
//!
//! ## Implement a new graphic device
//!
//! The following two things are needed to implement a graphic device.
//!
//! - [DeviceDriver] trait: the actual implementation of graphic device methods.
//! - [DeviceDescriptor] struct: the parameters that might differ per device
//!   instance (e.g. sizes, and colors).
//!
//! For example, the following code implements a simple graphic device that shows a message when it's
//! activated (and ignores everything else).
//!
//! ```
//! use extendr_api::{
//!     graphics::{DeviceDescriptor, DeviceDriver, DevDesc},
//!     prelude::*,
//! };
//!
//! struct MyDevice<'a> {
//!     welcome_message: &'a str,
//! }
//!
//! impl<'a> DeviceDriver for MyDevice<'a> {
//!     fn activate(&mut self, _dd: DevDesc) {
//!         let welcome_message = self.welcome_message;
//!         rprintln!("message from device: {welcome_message}");
//!     }
//! }
//!
//! /// Create a new device.
//! ///
//! /// @export
//! #[extendr]
//! fn my_device(welcome_message: String) {
//!     let device_driver = MyDevice {
//!         welcome_message: welcome_message.as_str(),
//!     };
//!     
//!     let device_descriptor = DeviceDescriptor::new();
//!     let device = device_driver.create_device::<MyDevice>(device_descriptor, "my device");
//! }
//! ```
//!
//! This can be called from R.
//!
//! ```r
//! my_device("I'm so active!!!")
//! #> message from device: I'm so active!!!
//! ```

use crate::*;
use libR_sys::*;

// These are used in the callback functions.
pub use libR_sys::{DevDesc, R_GE_gcontext};

pub mod color;
pub mod device_descriptor;
pub mod device_driver;

use color::Color;
pub use device_descriptor::*;
pub use device_driver::*;

pub struct Context {
    context: R_GE_gcontext,
    xscale: (f64, f64),
    yscale: (f64, f64),
    offset: (f64, f64),
    scalar: f64,
}

#[derive(Clone, Debug, PartialEq)]
pub struct Device {
    inner: pGEDevDesc,
}

#[derive(Clone, Debug, PartialEq)]
pub struct Pattern {
    inner: Robj,
}

#[derive(Clone, Debug, PartialEq)]
pub struct TextMetric {
    pub ascent: f64,
    pub descent: f64,
    pub width: f64,
}

/// A row-major array of pixels. One pixel is 32-bit, whose each byte represents
/// alpha, blue, green, and red in the order.
#[derive(Clone, Debug, PartialEq)]
pub struct Raster<P: AsRef<[u32]>> {
    pub pixels: P,
    pub width: usize,
}

impl Device {
    pub(crate) fn inner(&self) -> pGEDevDesc {
        self.inner
    }

    // pub(crate) fn asref(&self) -> &GEDevDesc {
    //     unsafe { &*self.inner }
    // }

    // pub(crate) fn dev(&self) -> &DevDesc {
    //     unsafe { &*self.asref().dev }
    // }
}

#[derive(PartialEq, Debug, Clone)]
pub enum LineEnd {
    Round,
    Butt,
    Square,
}

#[derive(PartialEq, Debug, Clone)]
pub enum LineJoin {
    Round,
    Mitre,
    Bevel,
}

#[derive(PartialEq, Debug, Clone)]
pub enum LineType {
    Blank,
    Solid,
    Dashed,
    Dotted,
    DotDash,
    LongDash,
    TwoDash,
}

#[derive(PartialEq, Debug, Clone)]
pub enum Unit {
    Device,
    Normalized,
    Inches,
    CM,
}

#[derive(PartialEq, Debug, Clone)]
pub enum FontFace {
    Plain,
    Bold,
    Italic,
    BoldItalic,
    Symbol,
}

impl From<LineEnd> for R_GE_lineend {
    fn from(value: LineEnd) -> Self {
        match value {
            LineEnd::Round => Self::GE_ROUND_CAP,
            LineEnd::Butt => Self::GE_BUTT_CAP,
            LineEnd::Square => Self::GE_SQUARE_CAP,
        }
    }
}

impl From<LineJoin> for R_GE_linejoin {
    fn from(value: LineJoin) -> Self {
        match value {
            LineJoin::Round => Self::GE_ROUND_JOIN,
            LineJoin::Mitre => Self::GE_MITRE_JOIN,
            LineJoin::Bevel => Self::GE_BEVEL_JOIN,
        }
    }
}

impl LineType {
    fn to_i32(&self) -> i32 {
        match self {
            Self::Blank => LTY_BLANK as _,
            Self::Solid => LTY_SOLID as _,
            Self::Dashed => LTY_DASHED as _,
            Self::Dotted => LTY_DOTTED as _,
            Self::DotDash => LTY_DOTDASH as _,
            Self::LongDash => LTY_LONGDASH as _,
            Self::TwoDash => LTY_TWODASH as _,
        }
    }
}

impl FontFace {
    fn to_i32(&self) -> i32 {
        match self {
            Self::Plain => 1,
            Self::Bold => 2,
            Self::Italic => 3,
            Self::BoldItalic => 4,
            Self::Symbol => 5,
        }
    }
}

fn unit_to_ge(unit: Unit) -> GEUnit {
    match unit {
        Unit::Device => GEUnit::GE_DEVICE,
        Unit::Normalized => GEUnit::GE_NDC,
        Unit::Inches => GEUnit::GE_INCHES,
        Unit::CM => GEUnit::GE_CM,
    }
}

impl Context {
    pub fn from_device(dev: &Device, unit: Unit) -> Self {
        #[allow(unused_unsafe)]
        unsafe {
            let offset = dev.to_device_coords((0., 0.), unit.clone());
            let mut xscale = dev.to_device_coords((1., 0.), unit.clone());
            let mut yscale = dev.to_device_coords((0., 1.), unit);
            xscale.0 -= offset.0;
            xscale.1 -= offset.1;
            yscale.0 -= offset.0;
            yscale.1 -= offset.1;

            // sqrt(abs(det(m)))
            let scalar = (xscale.0 * yscale.1 - xscale.1 * yscale.0).abs().sqrt();

            let mut context = R_GE_gcontext {
                col: Color::rgb(0xff, 0xff, 0xff).to_i32(),
                fill: Color::rgb(0xc0, 0xc0, 0xc0).to_i32(),
                gamma: 1.0,
                lwd: 1.0,
                lty: 0,
                lend: R_GE_lineend::GE_ROUND_CAP,
                ljoin: R_GE_linejoin::GE_ROUND_JOIN,
                lmitre: 10.0,
                cex: 1.0,
                ps: 14.0,
                lineheight: 1.0,
                fontface: 1,
                fontfamily: [0; 201],

                #[cfg(use_r_ge_version_14)]
                patternFill: R_NilValue,
            };

            context
                .fontfamily
                .iter_mut()
                .zip(b"Helvetica".iter())
                .for_each(|(d, s)| *d = *s as i8);

            Self {
                context,
                xscale,
                yscale,
                offset,
                scalar,
            }
        }
    }

    /// Set the line or text color of a primitive.
    pub fn color(&mut self, col: Color) -> &mut Self {
        self.context.col = col.to_i32();
        self
    }

    /// Set the fill color of a primitive.
    pub fn fill(&mut self, fill: Color) -> &mut Self {
        self.context.fill = fill.to_i32();
        self
    }

    /// Set the gamma of the device. `out_color = in_color ** gamma`
    pub fn gamma(&mut self, gamma: f64) -> &mut Self {
        self.context.gamma = gamma;
        self
    }

    /// Set the width of the line in chosen units.
    pub fn line_width(&mut self, lwd: f64) -> &mut Self {
        self.context.lwd = (lwd * self.scalar).max(1.0);
        self
    }

    /// Set the type of the line.
    /// ```ignore
    /// Blank    => <invisible>
    /// Solid    => ------
    /// Dashed   => - - - -
    /// Dotted   => . . . .
    /// DotDash  => . - . -
    /// LongDash => --  --
    /// TwoDash  => . . - -
    /// ```
    pub fn line_type(&mut self, lty: LineType) -> &mut Self {
        self.context.lty = lty.to_i32();
        self
    }

    /// Set the line end type.
    /// ```ignore
    ///   LineEnd::RoundCap
    ///   LineEnd::ButtCap  
    ///   LineEnd::SquareCap
    /// ```
    pub fn line_end(&mut self, lend: LineEnd) -> &mut Self {
        self.context.lend = lend.into();
        self
    }

    /// Set the line join type.
    /// ```ignore
    ///   LineJoin::RoundJoin
    ///   LineJoin::MitreJoin
    ///   LineJoin::BevelJoin
    /// ```
    pub fn line_join(&mut self, ljoin: LineJoin) -> &mut Self {
        self.context.ljoin = ljoin.into();
        self
    }

    pub fn point_size(&mut self, ps: f64) -> &mut Self {
        self.context.ps = ps;
        self
    }

    /// Set the line miter limit - the point where the line becomes a bevel join.
    pub fn line_mitre(&mut self, lmitre: f64) -> &mut Self {
        self.context.lmitre = lmitre * self.scalar;
        self
    }

    /// Set the line height for text.
    pub fn line_height(&mut self, lineheight: f64) -> &mut Self {
        self.context.lineheight = lineheight;
        self
    }

    // pub fn char_extra_size(&mut self, cex: f64) -> &mut Self {
    //     self.context.cex = cex;
    //     self
    // }

    /// Set the font face.
    /// ```ignore
    ///   FontFace::PlainFont
    ///   FontFace::BoldFont
    ///   FontFace::ItalicFont
    ///   FontFace::BoldItalicFont
    ///   FontFace::SymbolFont
    /// ```
    pub fn font_face(&mut self, fontface: FontFace) -> &mut Self {
        self.context.fontface = fontface.to_i32();
        self
    }

    //
    pub fn font_family(&mut self, fontfamily: &str) -> &mut Self {
        let maxlen = self.context.fontfamily.len() - 1;

        for c in self.context.fontfamily.iter_mut() {
            *c = 0;
        }

        for (i, b) in fontfamily.bytes().enumerate().take(maxlen) {
            self.context.fontfamily[i] = b as std::os::raw::c_char;
        }
        self
    }

    /// Set the transform as a 3x2 matrix.
    pub fn transform(
        &mut self,
        xscale: (f64, f64),
        yscale: (f64, f64),
        offset: (f64, f64),
    ) -> &mut Self {
        self.xscale = xscale;
        self.yscale = yscale;
        self.offset = offset;
        self
    }

    pub(crate) fn context(&self) -> pGEcontext {
        unsafe { std::mem::transmute(&self.context) }
    }

    // Affine transform.
    pub(crate) fn t(&self, xy: (f64, f64)) -> (f64, f64) {
        (
            self.offset.0 + xy.0 * self.xscale.0 + xy.1 * self.yscale.0,
            self.offset.1 + xy.0 * self.xscale.1 + xy.1 * self.yscale.1,
        )
    }

    // Affine relative transform (width, height).
    pub(crate) fn trel(&self, wh: (f64, f64)) -> (f64, f64) {
        (
            wh.0 * self.xscale.0 + wh.1 * self.yscale.0,
            wh.0 * self.xscale.1 + wh.1 * self.yscale.1,
        )
    }

    // Scalar transform (eg. radius etc).
    pub(crate) fn ts(&self, value: f64) -> f64 {
        value * self.scalar
    }

    // Inverse scalar transform (eg. text width etc).
    pub(crate) fn its(&self, value: f64) -> f64 {
        value / self.scalar
    }

    pub(crate) fn tmetric(&self, tm: TextMetric) -> TextMetric {
        TextMetric {
            ascent: tm.ascent / self.scalar,
            descent: tm.descent / self.scalar,
            width: tm.width / self.scalar,
        }
    }
}

#[allow(non_snake_case)]
impl Device {
    /// Get the current device.
    pub fn current() -> Result<Device> {
        // At present we can't trap an R error from a function
        // that does not return a SEXP.
        unsafe {
            Ok(Device {
                inner: GEcurrentDevice(),
            })
        }
    }

    /// Enable device rendering.
    pub fn mode_on(&self) -> Result<()> {
        unsafe {
            if Rf_NoDevices() != 0 {
                Err(Error::NoGraphicsDevices(Robj::from(())))
            } else {
                GEMode(1, self.inner());
                Ok(())
            }
        }
    }

    /// Disable device rendering and flush.
    pub fn mode_off(&self) -> Result<()> {
        unsafe {
            if Rf_NoDevices() != 0 {
                Err(Error::NoGraphicsDevices(Robj::from(())))
            } else {
                GEMode(0, self.inner());
                Ok(())
            }
        }
    }

    /// Get the device number for this device.
    pub fn device_number(&self) -> i32 {
        unsafe { GEdeviceNumber(self.inner()) }
    }

    /// Get a device by number.
    pub fn get_device(number: i32) -> Result<Device> {
        unsafe {
            if number < 0 || number >= Rf_NumDevices() {
                Err(Error::NoGraphicsDevices(Robj::from(())))
            } else {
                Ok(Device {
                    inner: GEgetDevice(number),
                })
            }
        }
    }

    /// Convert device coordinates into a specified unit.
    /// This is usually done by the API.
    pub fn from_device_coords(&self, value: (f64, f64), from: Unit) -> (f64, f64) {
        let from = unit_to_ge(from);
        unsafe {
            (
                GEfromDeviceX(value.0, from, self.inner()),
                GEfromDeviceY(value.1, from, self.inner()),
            )
        }
    }

    /// Convert a specified unit coordinates into device coordinates.
    /// This is usually done by the API.
    pub fn to_device_coords(&self, value: (f64, f64), to: Unit) -> (f64, f64) {
        if to == Unit::Device {
            value
        } else {
            let to = unit_to_ge(to);
            unsafe {
                (
                    GEtoDeviceX(value.0, to, self.inner()),
                    GEtoDeviceY(value.1, to, self.inner()),
                )
            }
        }
    }

    /// Convert device width/height coordinates into a specified unit.
    /// This is usually done by the API.
    pub fn from_device_wh(&self, value: (f64, f64), from: Unit) -> (f64, f64) {
        let from = unit_to_ge(from);
        unsafe {
            (
                GEfromDeviceWidth(value.0, from, self.inner()),
                GEfromDeviceHeight(value.1, from, self.inner()),
            )
        }
    }

    /// Convert a specified unit width/height coordinates into device coordinates.
    /// This is usually done by the API.
    pub fn to_device_wh(&self, value: (f64, f64), to: Unit) -> (f64, f64) {
        let to = unit_to_ge(to);
        unsafe {
            (
                GEtoDeviceWidth(value.0, to, self.inner()),
                GEtoDeviceHeight(value.1, to, self.inner()),
            )
        }
    }

    /// Start a new page. The page color can be set in advance.
    pub fn new_page(&self, gc: &Context) {
        unsafe { GENewPage(gc.context(), self.inner()) }
    }

    /// Change the clip rectangle.
    pub fn clip(&self, from: (f64, f64), to: (f64, f64), gc: &Context) {
        let from = gc.t(from);
        let to = gc.t(to);
        unsafe { GESetClip(from.0, from.1, to.0, to.1, self.inner()) }
    }

    /// Draw a stroked line. gc.color() is the stroke color.
    pub fn line(&self, from: (f64, f64), to: (f64, f64), gc: &Context) {
        let from = gc.t(from);
        let to = gc.t(to);
        unsafe { GELine(from.0, from.1, to.0, to.1, gc.context(), self.inner()) }
    }

    /// Draw a stroked/filled polyline. gc.color() is the stroke color.
    /// The input is anything yielding (x,y) coordinate pairs.
    /// Polylines are not closed.
    pub fn polyline<T: IntoIterator<Item = (f64, f64)>>(&self, coords: T, gc: &Context) {
        let (mut x, mut y): (Vec<_>, Vec<_>) = coords.into_iter().map(|xy| gc.t(xy)).unzip();
        let xptr = x.as_mut_slice().as_mut_ptr();
        let yptr = y.as_mut_slice().as_mut_ptr();
        unsafe {
            GEPolyline(
                x.len() as std::os::raw::c_int,
                xptr,
                yptr,
                gc.context(),
                self.inner(),
            )
        }
    }

    /// Draw a stroked/filled polygon. gc.color() is the stroke color.
    /// The input is anything yielding (x,y) coordinate pairs.
    /// Polygons are closed.
    pub fn polygon<T: IntoIterator<Item = (f64, f64)>>(&self, coords: T, gc: &Context) {
        let (mut x, mut y): (Vec<_>, Vec<_>) = coords.into_iter().map(|xy| gc.t(xy)).unzip();
        let xptr = x.as_mut_slice().as_mut_ptr();
        let yptr = y.as_mut_slice().as_mut_ptr();
        unsafe {
            GEPolygon(
                x.len() as std::os::raw::c_int,
                xptr,
                yptr,
                gc.context(),
                self.inner(),
            )
        }
    }

    // /// Return a list of (x, y) points generated from a spline.
    // /// The iterator returns ((x, y), s) where s is -1 to 1.
    // pub fn xspline<T: Iterator<Item = ((f64, f64), f64)> + Clone>(
    //     &self,
    //     coords: T,
    //     open: bool,
    //     rep_ends: bool,
    //     draw: bool,
    //     gc: &Context,
    // ) -> Robj {
    //     let (mut x, mut y): (Vec<_>, Vec<_>) = coords
    //         .clone()
    //         .map(|(xy, _s)| gc.t(xy))
    //         .unzip();
    //     let mut s: Vec<_> = coords.map(|(_xy, s)| s).collect();
    //     let xptr = x.as_mut_slice().as_mut_ptr();
    //     let yptr = y.as_mut_slice().as_mut_ptr();
    //     let sptr = s.as_mut_slice().as_mut_ptr();
    //     unsafe {
    //         new_owned(GEXspline(
    //             x.len() as std::os::raw::c_int,
    //             xptr,
    //             yptr,
    //             sptr,
    //             if open { 1 } else { 0 },
    //             if rep_ends { 1 } else { 0 },
    //             if draw { 1 } else { 0 },
    //             gc.context(),
    //             self.inner(),
    //         ))
    //     }
    // }

    /// Draw a stroked/filled circle.
    /// gc.color() is the stroke color.
    /// gc.fill() is the fill color.
    pub fn circle(&self, center: (f64, f64), radius: f64, gc: &Context) {
        let center = gc.t(center);
        let radius = gc.ts(radius);
        unsafe { GECircle(center.0, center.1, radius, gc.context(), self.inner()) }
    }

    /// Draw a stroked/filled axis-aligned rectangle.
    /// gc.color() is the stroke color.
    /// gc.fill() is the fill color.
    pub fn rect(&self, from: (f64, f64), to: (f64, f64), gc: &Context) {
        let from = gc.t(from);
        let to = gc.t(to);
        unsafe { GERect(from.0, from.1, to.0, to.1, gc.context(), self.inner()) }
    }

    /// Draw a path with multiple segments.
    /// gc.color() is the stroke color.
    /// gc.fill() is the fill color.
    /// The input is an interator of iterators yielding (x,y) pairs.
    pub fn path<T: IntoIterator<Item = impl IntoIterator<Item = (f64, f64)>>>(
        &self,
        coords: T,
        winding: bool,
        gc: &Context,
    ) {
        let mut x = Vec::new();
        let mut y = Vec::new();
        let mut nper: Vec<std::os::raw::c_int> = Vec::new();
        let coords = coords.into_iter();
        for segment in coords {
            let mut n = 0;
            for xy in segment {
                let xy = gc.t(xy);
                x.push(xy.0);
                y.push(xy.1);
                n += 1;
            }
            nper.push(n);
        }

        let xptr = x.as_mut_slice().as_mut_ptr();
        let yptr = y.as_mut_slice().as_mut_ptr();
        let nperptr = nper.as_mut_slice().as_mut_ptr();
        unsafe {
            GEPath(
                xptr,
                yptr,
                nper.len() as std::os::raw::c_int,
                nperptr,
                winding.into(),
                gc.context(),
                self.inner(),
            )
        }
    }

    /// Screen capture. Returns an integer matrix representing pixels if it is able.
    pub fn capture(&self) -> Robj {
        unsafe { Robj::from_sexp(GECap(self.inner())) }
    }

    /// Draw a bitmap.
    pub fn raster<T: AsRef<[u32]>>(
        &self,
        raster: Raster<T>,
        pos: (f64, f64),
        size: (f64, f64),
        angle: f64,
        interpolate: bool,
        gc: &Context,
    ) {
        let (x, y) = gc.t(pos);
        let (width, height) = gc.trel(size);
        let w = raster.width;
        let pixels = raster.pixels.as_ref();
        let h = pixels.len() / w;
        unsafe {
            let raster = pixels.as_ptr() as *mut u32;
            let w = w as i32;
            let h = h as i32;
            let interpolate = interpolate.into();
            GERaster(
                raster,
                w,
                h,
                x,
                y,
                width,
                height,
                angle,
                interpolate,
                gc.context(),
                self.inner(),
            )
        };
    }

    /// Draw a text string starting at pos.
    /// TODO: do we need to convert units?
    pub fn text<T: AsRef<str>>(
        &self,
        pos: (f64, f64),
        text: T,
        center: (f64, f64),
        rot: f64,
        gc: &Context,
    ) {
        unsafe {
            let (x, y) = gc.t(pos);
            let (xc, yc) = gc.trel(center);
            let text = std::ffi::CString::new(text.as_ref()).unwrap();
            let enc = cetype_t::CE_UTF8;
            GEText(
                x,
                y,
                text.as_ptr(),
                enc,
                xc,
                yc,
                rot,
                gc.context(),
                self.inner(),
            );
        }
    }

    /// Draw a special symbol centered on pos.
    /// See <https://stat.ethz.ch/R-manual/R-devel/library/graphics/html/points.html>
    pub fn symbol(&self, pos: (f64, f64), symbol: i32, size: f64, gc: &Context) {
        unsafe {
            let (x, y) = gc.t(pos);
            GESymbol(x, y, symbol, gc.ts(size), gc.context(), self.inner());
        }
    }

    /// Get the metrics for a single unicode codepoint.
    pub fn char_metric(&self, c: char, gc: &Context) -> TextMetric {
        unsafe {
            let mut res = TextMetric {
                ascent: 0.0,
                descent: 0.0,
                width: 0.0,
            };
            GEMetricInfo(
                c as i32,
                gc.context(),
                &mut res.ascent as *mut f64,
                &mut res.descent as *mut f64,
                &mut res.width as *mut f64,
                self.inner(),
            );
            gc.tmetric(res)
        }
    }

    /// Get the width of a unicode string.
    pub fn text_width<T: AsRef<str>>(&self, text: T, gc: &Context) -> f64 {
        let text = std::ffi::CString::new(text.as_ref()).unwrap();
        let enc = cetype_t::CE_UTF8;
        unsafe { gc.its(GEStrWidth(text.as_ptr(), enc, gc.context(), self.inner())) }
    }

    /// Get the height of a unicode string.
    pub fn text_height<T: AsRef<str>>(&self, text: T, gc: &Context) -> f64 {
        let text = std::ffi::CString::new(text.as_ref()).unwrap();
        let enc = cetype_t::CE_UTF8;
        unsafe { gc.its(GEStrHeight(text.as_ptr(), enc, gc.context(), self.inner())) }
    }

    /// Get the metrics for a unicode string.
    pub fn text_metric<T: AsRef<str>>(&self, text: T, gc: &Context) -> TextMetric {
        let text = std::ffi::CString::new(text.as_ref()).unwrap();
        let enc = cetype_t::CE_UTF8;
        unsafe {
            let mut res = TextMetric {
                ascent: 0.0,
                descent: 0.0,
                width: 0.0,
            };
            GEStrMetric(
                text.as_ptr(),
                enc,
                gc.context(),
                &mut res.ascent as *mut f64,
                &mut res.descent as *mut f64,
                &mut res.width as *mut f64,
                self.inner(),
            );
            gc.tmetric(res)
        }
    }

    /// Get the width of a mathematical expression.
    pub fn math_text_width(&self, expr: &Robj, gc: &Context) -> f64 {
        unsafe { gc.its(GEExpressionWidth(expr.get(), gc.context(), self.inner())) }
    }

    /// Get the height of a mathematical expression.
    pub fn math_text_height(&self, expr: &Robj, gc: &Context) -> f64 {
        unsafe { gc.its(GEExpressionHeight(expr.get(), gc.context(), self.inner())) }
    }

    /// Get the metrics for a mathematical expression.
    pub fn math_text_metric(&self, expr: &Robj, gc: &Context) -> TextMetric {
        unsafe {
            let mut res = TextMetric {
                ascent: 0.0,
                descent: 0.0,
                width: 0.0,
            };
            GEExpressionMetric(
                expr.get(),
                gc.context(),
                &mut res.ascent as *mut f64,
                &mut res.descent as *mut f64,
                &mut res.width as *mut f64,
                self.inner(),
            );
            gc.tmetric(res)
        }
    }

    /// Draw a mathematical expression.
    pub fn math_text(
        &self,
        expr: &Robj,
        pos: (f64, f64),
        center: (f64, f64),
        rot: f64,
        gc: &Context,
    ) {
        unsafe {
            let (x, y) = gc.t(pos);
            let (xc, yc) = gc.trel(center);
            GEMathText(x, y, expr.get(), xc, yc, rot, gc.context(), self.inner());
        }
    }
}