Support images in HTML export (#6578)

2 files changed, 105 insertions, 5 deletions

diff --git a/crates/typst-html/src/css.rs b/crates/typst-html/src/css.rs
index 2b659188..6c84cba0 100644
--- a/crates/typst-html/src/css.rs
+++ b/crates/typst-html/src/css.rs
@@ -1,11 +1,72 @@
 //! Conversion from Typst data types into CSS data types.
 
-use std::fmt::{self, Display};
+use std::fmt::{self, Display, Write};
 
-use typst_library::layout::Length;
+use ecow::EcoString;
+use typst_library::html::{attr, HtmlElem};
+use typst_library::layout::{Length, Rel};
 use typst_library::visualize::{Color, Hsl, LinearRgb, Oklab, Oklch, Rgb};
 use typst_utils::Numeric;
 
+/// Additional methods for [`HtmlElem`].
+pub trait HtmlElemExt {
+    /// Adds the styles to an element if the property list is non-empty.
+    fn with_styles(self, properties: Properties) -> Self;
+}
+
+impl HtmlElemExt for HtmlElem {
+    /// Adds CSS styles to an element.
+    fn with_styles(self, properties: Properties) -> Self {
+        if let Some(value) = properties.into_inline_styles() {
+            self.with_attr(attr::style, value)
+        } else {
+            self
+        }
+    }
+}
+
+/// A list of CSS properties with values.
+#[derive(Debug, Default)]
+pub struct Properties(EcoString);
+
+impl Properties {
+    /// Creates an empty list.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Adds a new property to the list.
+    pub fn push(&mut self, property: &str, value: impl Display) {
+        if !self.0.is_empty() {
+            self.0.push_str("; ");
+        }
+        write!(&mut self.0, "{property}: {value}").unwrap();
+    }
+
+    /// Adds a new property in builder-style.
+    #[expect(unused)]
+    pub fn with(mut self, property: &str, value: impl Display) -> Self {
+        self.push(property, value);
+        self
+    }
+
+    /// Turns this into a string suitable for use as an inline `style`
+    /// attribute.
+    pub fn into_inline_styles(self) -> Option<EcoString> {
+        (!self.0.is_empty()).then_some(self.0)
+    }
+}
+
+pub fn rel(rel: Rel) -> impl Display {
+    typst_utils::display(move |f| match (rel.abs.is_zero(), rel.rel.is_zero()) {
+        (false, false) => {
+            write!(f, "calc({}% + {})", rel.rel.get(), length(rel.abs))
+        }
+        (true, false) => write!(f, "{}%", rel.rel.get()),
+        (_, true) => write!(f, "{}", length(rel.abs)),
+    })
+}
+
 pub fn length(length: Length) -> impl Display {
     typst_utils::display(move |f| match (length.abs.is_zero(), length.em.is_zero()) {
         (false, false) => {
diff --git a/crates/typst-html/src/rules.rs b/crates/typst-html/src/rules.rs
index f361bfbb..5bf25e79 100644
--- a/crates/typst-html/src/rules.rs
+++ b/crates/typst-html/src/rules.rs
@@ -3,12 +3,12 @@ use std::num::NonZeroUsize;
 use ecow::{eco_format, EcoVec};
 use typst_library::diag::warning;
 use typst_library::foundations::{
-    Content, NativeElement, NativeRuleMap, ShowFn, StyleChain, Target,
+    Content, NativeElement, NativeRuleMap, ShowFn, Smart, StyleChain, Target,
 };
 use typst_library::html::{attr, tag, HtmlAttrs, HtmlElem, HtmlTag};
 use typst_library::introspection::{Counter, Locator};
 use typst_library::layout::resolve::{table_to_cellgrid, Cell, CellGrid, Entry};
-use typst_library::layout::OuterVAlignment;
+use typst_library::layout::{OuterVAlignment, Sizing};
 use typst_library::model::{
     Attribution, CiteElem, CiteGroup, Destination, EmphElem, EnumElem, FigureCaption,
     FigureElem, HeadingElem, LinkElem, LinkTarget, ListElem, ParbreakElem, QuoteElem,
@@ -18,6 +18,9 @@ use typst_library::text::{
     HighlightElem, LinebreakElem, OverlineElem, RawElem, RawLine, SpaceElem, StrikeElem,
     SubElem, SuperElem, UnderlineElem,
 };
+use typst_library::visualize::ImageElem;
+
+use crate::css::{self, HtmlElemExt};
 
 /// Register show rules for the [HTML target](Target::Html).
 pub fn register(rules: &mut NativeRuleMap) {
@@ -47,6 +50,9 @@ pub fn register(rules: &mut NativeRuleMap) {
     rules.register(Html, HIGHLIGHT_RULE);
     rules.register(Html, RAW_RULE);
     rules.register(Html, RAW_LINE_RULE);
+
+    // Visualize.
+    rules.register(Html, IMAGE_RULE);
 }
 
 const STRONG_RULE: ShowFn<StrongElem> = |elem, _, _| {
@@ -338,7 +344,7 @@ fn show_cellgrid(grid: CellGrid, styles: StyleChain) -> Content {
 fn show_cell(tag: HtmlTag, cell: &Cell, styles: StyleChain) -> Content {
     let cell = cell.body.clone();
     let Some(cell) = cell.to_packed::<TableCell>() else { return cell };
-    let mut attrs = HtmlAttrs::default();
+    let mut attrs = HtmlAttrs::new();
     let span = |n: NonZeroUsize| (n != NonZeroUsize::MIN).then(|| n.to_string());
     if let Some(colspan) = span(cell.colspan.get(styles)) {
         attrs.push(attr::colspan, colspan);
@@ -409,3 +415,36 @@ const RAW_RULE: ShowFn<RawElem> = |elem, _, styles| {
 };
 
 const RAW_LINE_RULE: ShowFn<RawLine> = |elem, _, _| Ok(elem.body.clone());
+
+const IMAGE_RULE: ShowFn<ImageElem> = |elem, engine, styles| {
+    let image = elem.decode(engine, styles)?;
+
+    let mut attrs = HtmlAttrs::new();
+    attrs.push(attr::src, typst_svg::convert_image_to_base64_url(&image));
+
+    if let Some(alt) = elem.alt.get_cloned(styles) {
+        attrs.push(attr::alt, alt);
+    }
+
+    let mut inline = css::Properties::new();
+
+    // TODO: Exclude in semantic profile.
+    if let Some(value) = typst_svg::convert_image_scaling(image.scaling()) {
+        inline.push("image-rendering", value);
+    }
+
+    // TODO: Exclude in semantic profile?
+    match elem.width.get(styles) {
+        Smart::Auto => {}
+        Smart::Custom(rel) => inline.push("width", css::rel(rel)),
+    }
+
+    // TODO: Exclude in semantic profile?
+    match elem.height.get(styles) {
+        Sizing::Auto => {}
+        Sizing::Rel(rel) => inline.push("height", css::rel(rel)),
+        Sizing::Fr(_) => {}
+    }
+
+    Ok(HtmlElem::new(tag::img).with_attrs(attrs).with_styles(inline).pack())
+};