lib.rs - source
Description: Source of the Rust file `crates/c-api/lib.rs`.

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    // Copyright 2020 the Resvg Authors
    // SPDX-License-Identifier: Apache-2.0 OR MIT

    //! C bindings.

    #![allow(non_camel_case_types)]
    #![warn(missing_docs)]
    #![warn(missing_copy_implementations)]

    use std::ffi::CStr;
    use std::os::raw::c_char;
    use std::slice;

    use resvg::tiny_skia;
    use resvg::usvg;

    /// @brief List of possible errors.
    #[repr(C)]
    #[derive(Copy, Clone)]
    pub enum resvg_error {
        /// Everything is ok.
        OK = 0,
        /// Only UTF-8 content are supported.
        NOT_AN_UTF8_STR,
        /// Failed to open the provided file.
        FILE_OPEN_FAILED,
        /// Compressed SVG must use the GZip algorithm.
        MALFORMED_GZIP,
        /// We do not allow SVG with more than 1_000_000 elements for security reasons.
        ELEMENTS_LIMIT_REACHED,
        /// SVG doesn't have a valid size.
        ///
        /// Occurs when width and/or height are <= 0.
        ///
        /// Also occurs if width, height and viewBox are not set.
        INVALID_SIZE,
        /// Failed to parse an SVG data.
        PARSING_FAILED,
    }

    /// @brief A rectangle representation.
    #[repr(C)]
    #[allow(missing_docs)]
    #[derive(Copy, Clone)]
    pub struct resvg_rect {
        pub x: f32,
        pub y: f32,
        pub width: f32,
        pub height: f32,
    }

    /// @brief A size representation.
    #[repr(C)]
    #[allow(missing_docs)]
    #[derive(Copy, Clone)]
    pub struct resvg_size {
        pub width: f32,
        pub height: f32,
    }

    /// @brief A 2D transform representation.
    #[repr(C)]
    #[allow(missing_docs)]
    #[derive(Copy, Clone)]
    pub struct resvg_transform {
        pub a: f32,
        pub b: f32,
        pub c: f32,
        pub d: f32,
        pub e: f32,
        pub f: f32,
    }

    impl resvg_transform {
        #[inline]
        fn to_tiny_skia(&self) -> tiny_skia::Transform {
            tiny_skia::Transform::from_row(self.a, self.b, self.c, self.d, self.e, self.f)
        }
    }

    /// @brief Creates an identity transform.
    #[no_mangle]
    pub extern "C" fn resvg_transform_identity() -> resvg_transform {
        resvg_transform {
            a: 1.0,
            b: 0.0,
            c: 0.0,
            d: 1.0,
            e: 0.0,
            f: 0.0,
        }
    }

    /// @brief Initializes the library log.
    ///
    /// Use it if you want to see any warnings.
    ///
    /// Must be called only once.
    ///
    /// All warnings will be printed to the `stderr`.
    #[no_mangle]
    pub extern "C" fn resvg_init_log() {
        if let Ok(()) = log::set_logger(&LOGGER) {
            log::set_max_level(log::LevelFilter::Warn);
        }
    }

    /// @brief An SVG to #resvg_render_tree conversion options.
    ///
    /// Also, contains a fonts database used during text to path conversion.
    /// The database is empty by default.
    pub struct resvg_options {
        options: usvg::Options<'static>,
    }

    /// @brief Creates a new #resvg_options object.
    ///
    /// Should be destroyed via #resvg_options_destroy.
    #[no_mangle]
    pub extern "C" fn resvg_options_create() -> *mut resvg_options {
        Box::into_raw(Box::new(resvg_options {
            options: usvg::Options::default(),
        }))
    }

    #[inline]
    fn cast_opt(opt: *mut resvg_options) -> &'static mut usvg::Options<'static> {
        unsafe {
            assert!(!opt.is_null());
            &mut (*opt).options
        }
    }

    /// @brief Sets a directory that will be used during relative paths resolving.
    ///
    /// Expected to be the same as the directory that contains the SVG file,
    /// but can be set to any.
    ///
    /// Must be UTF-8. Can be set to NULL.
    ///
    /// Default: NULL
    #[no_mangle]
    pub extern "C" fn resvg_options_set_resources_dir(opt: *mut resvg_options, path: *const c_char) {
        if path.is_null() {
            cast_opt(opt).resources_dir = None;
        } else {
            cast_opt(opt).resources_dir = Some(cstr_to_str(path).unwrap().into());
        }
    }

    /// @brief Sets the target DPI.
    ///
    /// Impact units conversion.
    ///
    /// Default: 96
    #[no_mangle]
    pub extern "C" fn resvg_options_set_dpi(opt: *mut resvg_options, dpi: f32) {
        cast_opt(opt).dpi = dpi;
    }

    /// @brief Provides the content of a stylesheet that will be used when resolving CSS attributes.
    ///
    /// Must be UTF-8. Can be set to NULL.
    ///
    /// Default: NULL
    #[no_mangle]
    pub extern "C" fn resvg_options_set_stylesheet(opt: *mut resvg_options, content: *const c_char) {
        if content.is_null() {
            cast_opt(opt).style_sheet = None;
        } else {
            cast_opt(opt).style_sheet = Some(cstr_to_str(content).unwrap().into());
        }
    }

    /// @brief Sets the default font family.
    ///
    /// Will be used when no `font-family` attribute is set in the SVG.
    ///
    /// Must be UTF-8. NULL is not allowed.
    ///
    /// Default: Times New Roman
    #[no_mangle]
    pub extern "C" fn resvg_options_set_font_family(opt: *mut resvg_options, family: *const c_char) {
        cast_opt(opt).font_family = cstr_to_str(family).unwrap().to_string();
    }

    /// @brief Sets the default font size.
    ///
    /// Will be used when no `font-size` attribute is set in the SVG.
    ///
    /// Default: 12
    #[no_mangle]
    pub extern "C" fn resvg_options_set_font_size(opt: *mut resvg_options, size: f32) {
        cast_opt(opt).font_size = size;
    }

    /// @brief Sets the `serif` font family.
    ///
    /// Must be UTF-8. NULL is not allowed.
    ///
    /// Has no effect when the `text` feature is not enabled.
    ///
    /// Default: Times New Roman
    #[no_mangle]
    #[allow(unused_variables)]
    pub extern "C" fn resvg_options_set_serif_family(opt: *mut resvg_options, family: *const c_char) {
        #[cfg(feature = "text")]
        {
            cast_opt(opt)
                .fontdb_mut()
                .set_serif_family(cstr_to_str(family).unwrap().to_string());
        }
    }

    /// @brief Sets the `sans-serif` font family.
    ///
    /// Must be UTF-8. NULL is not allowed.
    ///
    /// Has no effect when the `text` feature is not enabled.
    ///
    /// Default: Arial
    #[no_mangle]
    #[allow(unused_variables)]
    pub extern "C" fn resvg_options_set_sans_serif_family(
        opt: *mut resvg_options,
        family: *const c_char,
    ) {
        #[cfg(feature = "text")]
        {
            cast_opt(opt)
                .fontdb_mut()
                .set_sans_serif_family(cstr_to_str(family).unwrap().to_string());
        }
    }

    /// @brief Sets the `cursive` font family.
    ///
    /// Must be UTF-8. NULL is not allowed.
    ///
    /// Has no effect when the `text` feature is not enabled.
    ///
    /// Default: Comic Sans MS
    #[no_mangle]
    #[allow(unused_variables)]
    pub extern "C" fn resvg_options_set_cursive_family(opt: *mut resvg_options, family: *const c_char) {
        #[cfg(feature = "text")]
        {
            cast_opt(opt)
                .fontdb_mut()
                .set_cursive_family(cstr_to_str(family).unwrap().to_string());
        }
    }

    /// @brief Sets the `fantasy` font family.
    ///
    /// Must be UTF-8. NULL is not allowed.
    ///
    /// Has no effect when the `text` feature is not enabled.
    ///
    /// Default: Papyrus on macOS, Impact on other OS'es
    #[no_mangle]
    #[allow(unused_variables)]
    pub extern "C" fn resvg_options_set_fantasy_family(opt: *mut resvg_options, family: *const c_char) {
        #[cfg(feature = "text")]
        {
            cast_opt(opt)
                .fontdb_mut()
                .set_fantasy_family(cstr_to_str(family).unwrap().to_string());
        }
    }

    /// @brief Sets the `monospace` font family.
    ///
    /// Must be UTF-8. NULL is not allowed.
    ///
    /// Has no effect when the `text` feature is not enabled.
    ///
    /// Default: Courier New
    #[no_mangle]
    #[allow(unused_variables)]
    pub extern "C" fn resvg_options_set_monospace_family(
        opt: *mut resvg_options,
        family: *const c_char,
    ) {
        #[cfg(feature = "text")]
        {
            cast_opt(opt)
                .fontdb_mut()
                .set_monospace_family(cstr_to_str(family).unwrap().to_string());
        }
    }

    /// @brief Sets a comma-separated list of languages.
    ///
    /// Will be used to resolve a `systemLanguage` conditional attribute.
    ///
    /// Example: en,en-US.
    ///
    /// Must be UTF-8. Can be NULL.
    ///
    /// Default: en
    #[no_mangle]
    pub extern "C" fn resvg_options_set_languages(opt: *mut resvg_options, languages: *const c_char) {
        if languages.is_null() {
            cast_opt(opt).languages = Vec::new();
            return;
        }

        let languages_str = match cstr_to_str(languages) {
            Some(v) => v,
            None => return,
        };

        let mut languages = Vec::new();
        for lang in languages_str.split(',') {
            languages.push(lang.trim().to_string());
        }

        cast_opt(opt).languages = languages;
    }

    /// @brief A shape rendering method.
    #[repr(C)]
    #[allow(missing_docs)]
    #[derive(Copy, Clone)]
    pub enum resvg_shape_rendering {
        OPTIMIZE_SPEED,
        CRISP_EDGES,
        GEOMETRIC_PRECISION,
    }

    /// @brief Sets the default shape rendering method.
    ///
    /// Will be used when an SVG element's `shape-rendering` property is set to `auto`.
    ///
    /// Default: `RESVG_SHAPE_RENDERING_GEOMETRIC_PRECISION`
    #[no_mangle]
    pub extern "C" fn resvg_options_set_shape_rendering_mode(
        opt: *mut resvg_options,
        mode: resvg_shape_rendering,
    ) {
        cast_opt(opt).shape_rendering = match mode as i32 {
            0 => usvg::ShapeRendering::OptimizeSpeed,
            1 => usvg::ShapeRendering::CrispEdges,
            2 => usvg::ShapeRendering::GeometricPrecision,
            _ => return,
        }
    }

    /// @brief A text rendering method.
    #[repr(C)]
    #[allow(missing_docs)]
    #[derive(Copy, Clone)]
    pub enum resvg_text_rendering {
        OPTIMIZE_SPEED,
        OPTIMIZE_LEGIBILITY,
        GEOMETRIC_PRECISION,
    }

    /// @brief Sets the default text rendering method.
    ///
    /// Will be used when an SVG element's `text-rendering` property is set to `auto`.
    ///
    /// Default: `RESVG_TEXT_RENDERING_OPTIMIZE_LEGIBILITY`
    #[no_mangle]
    pub extern "C" fn resvg_options_set_text_rendering_mode(
        opt: *mut resvg_options,
        mode: resvg_text_rendering,
    ) {
        cast_opt(opt).text_rendering = match mode as i32 {
            0 => usvg::TextRendering::OptimizeSpeed,
            1 => usvg::TextRendering::OptimizeLegibility,
            2 => usvg::TextRendering::GeometricPrecision,
            _ => return,
        }
    }

    /// @brief A image rendering method.
    #[repr(C)]
    #[allow(missing_docs)]
    #[derive(Copy, Clone)]
    pub enum resvg_image_rendering {
        OPTIMIZE_QUALITY,
        OPTIMIZE_SPEED,
    }

    /// @brief Sets the default image rendering method.
    ///
    /// Will be used when an SVG element's `image-rendering` property is set to `auto`.
    ///
    /// Default: `RESVG_IMAGE_RENDERING_OPTIMIZE_QUALITY`
    #[no_mangle]
    pub extern "C" fn resvg_options_set_image_rendering_mode(
        opt: *mut resvg_options,
        mode: resvg_image_rendering,
    ) {
        cast_opt(opt).image_rendering = match mode as i32 {
            0 => usvg::ImageRendering::OptimizeQuality,
            1 => usvg::ImageRendering::OptimizeSpeed,
            _ => return,
        }
    }

    /// @brief Loads a font data into the internal fonts database.
    ///
    /// Prints a warning into the log when the data is not a valid TrueType font.
    ///
    /// Has no effect when the `text` feature is not enabled.
    #[no_mangle]
    #[allow(unused_variables)]
    pub extern "C" fn resvg_options_load_font_data(
        opt: *mut resvg_options,
        data: *const c_char,
        len: usize,
    ) {
        #[cfg(feature = "text")]
        {
            let data = unsafe { slice::from_raw_parts(data as *const u8, len) };
            cast_opt(opt).fontdb_mut().load_font_data(data.to_vec())
        }
    }

    /// @brief Loads a font file into the internal fonts database.
    ///
    /// Prints a warning into the log when the data is not a valid TrueType font.
    ///
    /// Has no effect when the `text` feature is not enabled.
    ///
    /// @return #resvg_error with RESVG_OK, RESVG_ERROR_NOT_AN_UTF8_STR or RESVG_ERROR_FILE_OPEN_FAILED
    #[no_mangle]
    #[allow(unused_variables)]
    pub extern "C" fn resvg_options_load_font_file(
        opt: *mut resvg_options,
        file_path: *const c_char,
    ) -> i32 {
        #[cfg(feature = "text")]
        {
            let file_path = match cstr_to_str(file_path) {
                Some(v) => v,
                None => return resvg_error::NOT_AN_UTF8_STR as i32,
            };

            if cast_opt(opt).fontdb_mut().load_font_file(file_path).is_ok() {
                resvg_error::OK as i32
            } else {
                resvg_error::FILE_OPEN_FAILED as i32
            }
        }

        #[cfg(not(feature = "text"))]
        {
            resvg_error::OK as i32
        }
    }

    /// @brief Loads system fonts into the internal fonts database.
    ///
    /// This method is very IO intensive.
    ///
    /// This method should be executed only once per #resvg_options.
    ///
    /// The system scanning is not perfect, so some fonts may be omitted.
    /// Please send a bug report in this case.
    ///
    /// Prints warnings into the log.
    ///
    /// Has no effect when the `text` feature is not enabled.
    #[no_mangle]
    #[allow(unused_variables)]
    pub extern "C" fn resvg_options_load_system_fonts(opt: *mut resvg_options) {
        #[cfg(feature = "text")]
        {
            cast_opt(opt).fontdb_mut().load_system_fonts();
        }
    }

    /// @brief Destroys the #resvg_options.
    #[no_mangle]
    pub extern "C" fn resvg_options_destroy(opt: *mut resvg_options) {
        unsafe {
            assert!(!opt.is_null());
            let _ = Box::from_raw(opt);
        };
    }

    // TODO: use resvg::Tree
    /// @brief An opaque pointer to the rendering tree.
    pub struct resvg_render_tree(pub usvg::Tree);

    /// @brief Creates #resvg_render_tree from file.
    ///
    /// .svg and .svgz files are supported.
    ///
    /// See #resvg_is_image_empty for details.
    ///
    /// @param file_path UTF-8 file path.
    /// @param opt Rendering options. Must not be NULL.
    /// @param tree Parsed render tree. Should be destroyed via #resvg_tree_destroy.
    /// @return #resvg_error
    #[no_mangle]
    pub extern "C" fn resvg_parse_tree_from_file(
        file_path: *const c_char,
        opt: *const resvg_options,
        tree: *mut *mut resvg_render_tree,
    ) -> i32 {
        let file_path = match cstr_to_str(file_path) {
            Some(v) => v,
            None => return resvg_error::NOT_AN_UTF8_STR as i32,
        };

        let raw_opt = unsafe {
            assert!(!opt.is_null());
            &*opt
        };

        let file_data = match std::fs::read(file_path) {
            Ok(tree) => tree,
            Err(_) => return resvg_error::FILE_OPEN_FAILED as i32,
        };

        let utree = usvg::Tree::from_data(&file_data, &raw_opt.options);

        let utree = match utree {
            Ok(tree) => tree,
            Err(e) => return convert_error(e) as i32,
        };

        let tree_box = Box::new(resvg_render_tree(utree));
        unsafe {
            *tree = Box::into_raw(tree_box);
        }

        resvg_error::OK as i32
    }

    /// @brief Creates #resvg_render_tree from data.
    ///
    /// See #resvg_is_image_empty for details.
    ///
    /// @param data SVG data. Can contain SVG string or gzip compressed data. Must not be NULL.
    /// @param len Data length.
    /// @param opt Rendering options. Must not be NULL.
    /// @param tree Parsed render tree. Should be destroyed via #resvg_tree_destroy.
    /// @return #resvg_error
    #[no_mangle]
    pub extern "C" fn resvg_parse_tree_from_data(
        data: *const c_char,
        len: usize,
        opt: *const resvg_options,
        tree: *mut *mut resvg_render_tree,
    ) -> i32 {
        let data = unsafe { slice::from_raw_parts(data as *const u8, len) };

        let raw_opt = unsafe {
            assert!(!opt.is_null());
            &*opt
        };

        let utree = usvg::Tree::from_data(data, &raw_opt.options);

        let utree = match utree {
            Ok(tree) => tree,
            Err(e) => return convert_error(e) as i32,
        };

        let tree_box = Box::new(resvg_render_tree(utree));
        unsafe {
            *tree = Box::into_raw(tree_box);
        }

        resvg_error::OK as i32
    }

    /// @brief Checks that tree has any nodes.
    ///
    /// @param tree Render tree.
    /// @return Returns `true` if tree has no nodes.
    #[no_mangle]
    pub extern "C" fn resvg_is_image_empty(tree: *const resvg_render_tree) -> bool {
        let tree = unsafe {
            assert!(!tree.is_null());
            &*tree
        };

        !tree.0.root().has_children()
    }

    /// @brief Returns an image size.
    ///
    /// The size of an image that is required to render this SVG.
    ///
    /// Note that elements outside the viewbox will be clipped. This is by design.
    /// If you want to render the whole SVG content, use #resvg_get_image_bbox instead.
    ///
    /// @param tree Render tree.
    /// @return Image size.
    #[no_mangle]
    pub extern "C" fn resvg_get_image_size(tree: *const resvg_render_tree) -> resvg_size {
        let tree = unsafe {
            assert!(!tree.is_null());
            &*tree
        };

        let size = tree.0.size();

        resvg_size {
            width: size.width(),
            height: size.height(),
        }
    }

    /// @brief Returns an object bounding box.
    ///
    /// This bounding box does not include objects stroke and filter regions.
    /// This is what SVG calls "absolute object bonding box".
    ///
    /// If you're looking for a "complete" bounding box see #resvg_get_image_bbox
    ///
    /// @param tree Render tree.
    /// @param bbox Image's object bounding box.
    /// @return `false` if an image has no elements.
    #[no_mangle]
    pub extern "C" fn resvg_get_object_bbox(
        tree: *const resvg_render_tree,
        bbox: *mut resvg_rect,
    ) -> bool {
        let tree = unsafe {
            assert!(!tree.is_null());
            &*tree
        };

        if let Some(r) = tree.0.root().abs_bounding_box().to_non_zero_rect() {
            unsafe {
                *bbox = resvg_rect {
                    x: r.x(),
                    y: r.y(),
                    width: r.width(),
                    height: r.height(),
                }
            }

            true
        } else {
            false
        }
    }

    /// @brief Returns an image bounding box.
    ///
    /// This bounding box contains the maximum SVG dimensions.
    /// It's size can be bigger or smaller than #resvg_get_image_size
    /// Use it when you want to avoid clipping of elements that are outside the SVG viewbox.
    ///
    /// @param tree Render tree.
    /// @param bbox Image's bounding box.
    /// @return `false` if an image has no elements.
    #[no_mangle]
    pub extern "C" fn resvg_get_image_bbox(
        tree: *const resvg_render_tree,
        bbox: *mut resvg_rect,
    ) -> bool {
        let tree = unsafe {
            assert!(!tree.is_null());
            &*tree
        };

        // `abs_layer_bounding_box` returns 0x0x1x1 for empty groups, so we need additional checks.
        if tree.0.root().has_children() || !tree.0.root().filters().is_empty() {
            let r = tree.0.root().abs_layer_bounding_box();
            unsafe {
                *bbox = resvg_rect {
                    x: r.x(),
                    y: r.y(),
                    width: r.width(),
                    height: r.height(),
                }
            }

            true
        } else {
            false
        }
    }

    /// @brief Returns `true` if a renderable node with such an ID exists.
    ///
    /// @param tree Render tree.
    /// @param id Node's ID. UTF-8 string. Must not be NULL.
    /// @return `true` if a node exists.
    /// @return `false` if a node doesn't exist or ID isn't a UTF-8 string.
    /// @return `false` if a node exists, but not renderable.
    #[no_mangle]
    pub extern "C" fn resvg_node_exists(tree: *const resvg_render_tree, id: *const c_char) -> bool {
        let id = match cstr_to_str(id) {
            Some(v) => v,
            None => {
                log::warn!("Provided ID is no an UTF-8 string.");
                return false;
            }
        };

        let tree = unsafe {
            assert!(!tree.is_null());
            &*tree
        };

        tree.0.node_by_id(id).is_some()
    }

    /// @brief Returns node's transform by ID.
    ///
    /// @param tree Render tree.
    /// @param id Node's ID. UTF-8 string. Must not be NULL.
    /// @param transform Node's transform.
    /// @return `true` if a node exists.
    /// @return `false` if a node doesn't exist or ID isn't a UTF-8 string.
    /// @return `false` if a node exists, but not renderable.
    #[no_mangle]
    pub extern "C" fn resvg_get_node_transform(
        tree: *const resvg_render_tree,
        id: *const c_char,
        transform: *mut resvg_transform,
    ) -> bool {
        let id = match cstr_to_str(id) {
            Some(v) => v,
            None => {
                log::warn!("Provided ID is no an UTF-8 string.");
                return false;
            }
        };

        let tree = unsafe {
            assert!(!tree.is_null());
            &*tree
        };

        if let Some(node) = tree.0.node_by_id(id) {
            let abs_ts = node.abs_transform();

            unsafe {
                *transform = resvg_transform {
                    a: abs_ts.sx,
                    b: abs_ts.ky,
                    c: abs_ts.kx,
                    d: abs_ts.sy,
                    e: abs_ts.tx,
                    f: abs_ts.ty,
                }
            }

            return true;
        }

        false
    }

    /// @brief Returns node's bounding box in canvas coordinates by ID.
    ///
    /// @param tree Render tree.
    /// @param id Node's ID. Must not be NULL.
    /// @param bbox Node's bounding box.
    /// @return `false` if a node with such an ID does not exist
    /// @return `false` if ID isn't a UTF-8 string.
    /// @return `false` if ID is an empty string
    #[no_mangle]
    pub extern "C" fn resvg_get_node_bbox(
        tree: *const resvg_render_tree,
        id: *const c_char,
        bbox: *mut resvg_rect,
    ) -> bool {
        get_node_bbox(tree, id, bbox, &|node| node.abs_bounding_box())
    }

    /// @brief Returns node's bounding box, including stroke, in canvas coordinates by ID.
    ///
    /// @param tree Render tree.
    /// @param id Node's ID. Must not be NULL.
    /// @param bbox Node's bounding box.
    /// @return `false` if a node with such an ID does not exist
    /// @return `false` if ID isn't a UTF-8 string.
    /// @return `false` if ID is an empty string
    #[no_mangle]
    pub extern "C" fn resvg_get_node_stroke_bbox(
        tree: *const resvg_render_tree,
        id: *const c_char,
        bbox: *mut resvg_rect,
    ) -> bool {
        get_node_bbox(tree, id, bbox, &|node| node.abs_stroke_bounding_box())
    }

    fn get_node_bbox(
        tree: *const resvg_render_tree,
        id: *const c_char,
        bbox: *mut resvg_rect,
        f: &dyn Fn(&usvg::Node) -> usvg::Rect,
    ) -> bool {
        let id = match cstr_to_str(id) {
            Some(v) => v,
            None => {
                log::warn!("Provided ID is no an UTF-8 string.");
                return false;
            }
        };

        if id.is_empty() {
            log::warn!("Node ID must not be empty.");
            return false;
        }

        let tree = unsafe {
            assert!(!tree.is_null());
            &*tree
        };

        match tree.0.node_by_id(id) {
            Some(node) => {
                let r = f(node);
                unsafe {
                    *bbox = resvg_rect {
                        x: r.x(),
                        y: r.y(),
                        width: r.width(),
                        height: r.height(),
                    }
                }
                true
            }
            None => {
                log::warn!("No node with '{}' ID is in the tree.", id);
                false
            }
        }
    }

    /// @brief Destroys the #resvg_render_tree.
    #[no_mangle]
    pub extern "C" fn resvg_tree_destroy(tree: *mut resvg_render_tree) {
        unsafe {
            assert!(!tree.is_null());
            let _ = Box::from_raw(tree);
        };
    }

    fn cstr_to_str(text: *const c_char) -> Option<&'static str> {
        let text = unsafe {
            assert!(!text.is_null());
            CStr::from_ptr(text)
        };

        text.to_str().ok()
    }

    fn convert_error(e: usvg::Error) -> resvg_error {
        match e {
            usvg::Error::NotAnUtf8Str => resvg_error::NOT_AN_UTF8_STR,
            usvg::Error::MalformedGZip => resvg_error::MALFORMED_GZIP,
            usvg::Error::ElementsLimitReached => resvg_error::ELEMENTS_LIMIT_REACHED,
            usvg::Error::InvalidSize => resvg_error::INVALID_SIZE,
            usvg::Error::ParsingFailed(_) => resvg_error::PARSING_FAILED,
        }
    }

    /// @brief Renders the #resvg_render_tree onto the pixmap.
    ///
    /// @param tree A render tree.
    /// @param transform A root SVG transform. Can be used to position SVG inside the `pixmap`.
    /// @param width Pixmap width.
    /// @param height Pixmap height.
    /// @param pixmap Pixmap data. Should have width*height*4 size and contain
    ///               premultiplied RGBA8888 pixels.
    #[no_mangle]
    pub extern "C" fn resvg_render(
        tree: *const resvg_render_tree,
        transform: resvg_transform,
        width: u32,
        height: u32,
        pixmap: *mut c_char,
    ) {
        let tree = unsafe {
            assert!(!tree.is_null());
            &*tree
        };

        let pixmap_len = width as usize * height as usize * tiny_skia::BYTES_PER_PIXEL;
        let pixmap: &mut [u8] =
            unsafe { std::slice::from_raw_parts_mut(pixmap as *mut u8, pixmap_len) };
        let mut pixmap = tiny_skia::PixmapMut::from_bytes(pixmap, width, height).unwrap();

        resvg::render(&tree.0, transform.to_tiny_skia(), &mut pixmap)
    }

    /// @brief Renders a Node by ID onto the image.
    ///
    /// @param tree A render tree.
    /// @param id Node's ID. Must not be NULL.
    /// @param transform A root SVG transform. Can be used to position SVG inside the `pixmap`.
    /// @param width Pixmap width.
    /// @param height Pixmap height.
    /// @param pixmap Pixmap data. Should have width*height*4 size and contain
    ///               premultiplied RGBA8888 pixels.
    /// @return `false` when `id` is not a non-empty UTF-8 string.
    /// @return `false` when the selected `id` is not present.
    /// @return `false` when an element has a zero bbox.
    #[no_mangle]
    pub extern "C" fn resvg_render_node(
        tree: *const resvg_render_tree,
        id: *const c_char,
        transform: resvg_transform,
        width: u32,
        height: u32,
        pixmap: *mut c_char,
    ) -> bool {
        let tree = unsafe {
            assert!(!tree.is_null());
            &*tree
        };

        let id = match cstr_to_str(id) {
            Some(v) => v,
            None => return false,
        };

        if id.is_empty() {
            log::warn!("Node with an empty ID cannot be rendered.");
            return false;
        }

        if let Some(node) = tree.0.node_by_id(id) {
            let pixmap_len = width as usize * height as usize * tiny_skia::BYTES_PER_PIXEL;
            let pixmap: &mut [u8] =
                unsafe { std::slice::from_raw_parts_mut(pixmap as *mut u8, pixmap_len) };
            let mut pixmap = tiny_skia::PixmapMut::from_bytes(pixmap, width, height).unwrap();

            resvg::render_node(node, transform.to_tiny_skia(), &mut pixmap).is_some()
        } else {
            log::warn!("A node with '{}' ID wasn't found.", id);
            false
        }
    }

    /// A simple stderr logger.
    static LOGGER: SimpleLogger = SimpleLogger;
    struct SimpleLogger;
    impl log::Log for SimpleLogger {
        fn enabled(&self, metadata: &log::Metadata) -> bool {
            metadata.level() <= log::LevelFilter::Warn
        }

        fn log(&self, record: &log::Record) {
            if self.enabled(record.metadata()) {
                let target = if record.target().len() > 0 {
                    record.target()
                } else {
                    record.module_path().unwrap_or_default()
                };

                let line = record.line().unwrap_or(0);
                let args = record.args();

                match record.level() {
                    log::Level::Error => eprintln!("Error (in {}:{}): {}", target, line, args),
                    log::Level::Warn => eprintln!("Warning (in {}:{}): {}", target, line, args),
                    log::Level::Info => eprintln!("Info (in {}:{}): {}", target, line, args),
                    log::Level::Debug => eprintln!("Debug (in {}:{}): {}", target, line, args),
                    log::Level::Trace => eprintln!("Trace (in {}:{}): {}", target, line, args),
                }
            }
        }

        fn flush(&self) {}
    }