render: resolve relative box edge lengths

crates/obscura-render/src/dom.rs

@@ -448,13 +448,38 @@ pub fn layout_dom_with_images(
                 }
                 inh.box_sizing = style.box_sizing;
 
-                // Percentage padding/margin resolve against the containing
-                // block WIDTH on every side (per CSS: `padding-top:56.25%` in a
-                // 1000px block is 562.5px, not a fraction of the height). The
-                // f32 Edges cannot carry a percentage, so bake the resolved px
-                // back into `padding`/`margin`, which then feed taffy.
+                // Resolve font/viewport-relative box edges now that their
+                // reference sizes are known. Percentage padding/margin then
+                // resolve against the containing block WIDTH on every side
+                // (per CSS: `padding-top:56.25%` in a 1000px block is 562.5px,
+                // not a fraction of the height). Bake the resolved px back into
+                // `padding`/`margin`, which then feed taffy.
                 let cb_w = inh.cb_width;
                 for i in 0..4 {
+                    if let Some(relative) = style.padding_relative[i] {
+                        if let crate::Dimension::Px(px) =
+                            relative.resolve(em_px, root_fs, vw, vh)
+                        {
+                            match i {
+                                0 => style.padding.top = px.max(0.0),
+                                1 => style.padding.right = px.max(0.0),
+                                2 => style.padding.bottom = px.max(0.0),
+                                _ => style.padding.left = px.max(0.0),
+                            }
+                        }
+                    }
+                    if let Some(relative) = style.margin_relative[i] {
+                        if let crate::Dimension::Px(px) =
+                            relative.resolve(em_px, root_fs, vw, vh)
+                        {
+                            match i {
+                                0 => style.margin.top = px,
+                                1 => style.margin.right = px,
+                                2 => style.margin.bottom = px,
+                                _ => style.margin.left = px,
+                            }
+                        }
+                    }
                     if let Some(frac) = style.padding_percent[i] {
                         let px = (frac * cb_w).max(0.0);
                         match i {

crates/obscura-render/src/lib.rs

@@ -197,6 +197,10 @@ pub struct LayoutStyle {
     /// percentage, so this is resolved to px during `dom::layout_dom`'s top-down
     /// pass once the containing-block width is known.
     pub margin_percent: [Option<f32>; 4],
+    /// Font- and viewport-relative margin lengths (top, right, bottom, left).
+    /// These retain their unit until the top-down pass knows the element font
+    /// size, root font size, and viewport dimensions.
+    pub margin_relative: [Option<Dimension>; 4],
     pub padding: Edges,
     /// Percentage padding per side (top, right, bottom, left) as a 0..1
     /// fraction, `None` when the side is a fixed length. All four sides resolve
@@ -206,6 +210,9 @@ pub struct LayoutStyle {
     /// resolved to px in `dom::layout_dom`'s top-down pass and written back into
     /// `padding`, which then feeds taffy as a fixed length.
     pub padding_percent: [Option<f32>; 4],
+    /// Font- and viewport-relative padding lengths (top, right, bottom, left),
+    /// resolved alongside `margin_relative` during the top-down pass.
+    pub padding_relative: [Option<Dimension>; 4],
     pub border: Edges,
     /// `border-radius` (uniform; the first value of the shorthand). Rounds the
     /// background fill and border. In px after resolution.

crates/obscura-render/src/style.rs

@@ -1672,12 +1672,31 @@ fn set_margin_side(style: &mut LayoutStyle, idx: usize, value: &str) {
     let is_auto = v.eq_ignore_ascii_case("auto");
     if let Some(frac) = percent_fraction(v) {
         style.margin_percent[idx] = Some(frac);
+        style.margin_relative[idx] = None;
         set_margin_px(&mut style.margin, idx, 0.0);
         style.margin_auto[idx] = false;
         return;
     }
-    let px = if is_auto { 0.0 } else { px(value).unwrap_or(0.0) };
+    let dimension = dimension_value(v);
+    match dimension {
+        crate::Dimension::Px(px) => {
             set_margin_px(&mut style.margin, idx, px);
+            style.margin_relative[idx] = None;
+        }
+        crate::Dimension::Em(_)
+        | crate::Dimension::Rem(_)
+        | crate::Dimension::Vw(_)
+        | crate::Dimension::Vh(_)
+        | crate::Dimension::Vmin(_)
+        | crate::Dimension::Vmax(_) => {
+            set_margin_px(&mut style.margin, idx, 0.0);
+            style.margin_relative[idx] = Some(dimension);
+        }
+        _ => {
+            set_margin_px(&mut style.margin, idx, 0.0);
+            style.margin_relative[idx] = None;
+        }
+    }
     style.margin_auto[idx] = is_auto;
     style.margin_percent[idx] = None;
 }
@@ -1696,15 +1715,32 @@ fn set_margin_px(margin: &mut Edges, idx: usize, px: f32) {
 /// recorded in `padding_percent` and resolved against the containing-block
 /// width during the top-down pass; a length is stored directly.
 fn set_padding_side(style: &mut LayoutStyle, idx: usize, value: &str) {
-    if let Some(frac) = percent_fraction(value.trim()) {
+    let value = value.trim();
+    if let Some(frac) = percent_fraction(value) {
         style.padding_percent[idx] = Some(frac);
+        style.padding_relative[idx] = None;
         set_padding_px(&mut style.padding, idx, 0.0);
         return;
     }
-    if let Some(px) = px(value) {
+    let dimension = dimension_value(value);
+    match dimension {
+        crate::Dimension::Px(px) => {
             set_padding_px(&mut style.padding, idx, px);
+            style.padding_relative[idx] = None;
             style.padding_percent[idx] = None;
         }
+        crate::Dimension::Em(_)
+        | crate::Dimension::Rem(_)
+        | crate::Dimension::Vw(_)
+        | crate::Dimension::Vh(_)
+        | crate::Dimension::Vmin(_)
+        | crate::Dimension::Vmax(_) => {
+            set_padding_px(&mut style.padding, idx, 0.0);
+            style.padding_relative[idx] = Some(dimension);
+            style.padding_percent[idx] = None;
+        }
+        _ => {}
+    }
 }
 
 fn set_padding_px(padding: &mut Edges, idx: usize, px: f32) {
@@ -2202,6 +2238,20 @@ mod tests {
         assert!(!s.margin_auto[3]);
     }
 
+    #[test]
+    fn relative_box_edges_remain_unresolved() {
+        let s = compute_style(
+            "div",
+            Some("font-size:20px;margin:15vh auto 2em 10vw;padding:1rem 2vmin"),
+        );
+        assert_eq!(s.margin_relative[0], Some(crate::Dimension::Vh(15.0)));
+        assert!(s.margin_auto[1]);
+        assert_eq!(s.margin_relative[2], Some(crate::Dimension::Em(2.0)));
+        assert_eq!(s.margin_relative[3], Some(crate::Dimension::Vw(10.0)));
+        assert_eq!(s.padding_relative[0], Some(crate::Dimension::Rem(1.0)));
+        assert_eq!(s.padding_relative[1], Some(crate::Dimension::Vmin(2.0)));
+    }
+
     #[test]
     fn ua_defaults_and_ignore_unknown() {
         let s = compute_style("span", Some("color: red; ; bogus: ; display: none"));