From 193e30deb541f4c7e8d73390d7003f7497f994cd Mon Sep 17 00:00:00 2001
From: SGavrl <277843151+SGavrl@users.noreply.github.com>
Date: Thu, 2 Jul 2026 19:47:08 +0000
Subject: [PATCH] feat(render): implement basic CSS cascade matching from
 <style> blocks

---
 Cargo.lock                         |  1 +
 crates/obscura-render/Cargo.toml   |  1 +
 crates/obscura-render/src/dom.rs   | 90 +++++++++++++++++++++++++++---
 crates/obscura-render/src/paint.rs | 14 ++---
 crates/obscura-render/src/style.rs |  4 +-
 5 files changed, 93 insertions(+), 17 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index c5ecce9..2472a3f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1880,6 +1880,7 @@ version = "0.1.0"
 dependencies = [
  "ab_glyph",
  "base64",
+ "cssparser",
  "image",
  "obscura-dom",
  "taffy",
diff --git a/crates/obscura-render/Cargo.toml b/crates/obscura-render/Cargo.toml
index 937c02f..9ddbe9f 100644
--- a/crates/obscura-render/Cargo.toml
+++ b/crates/obscura-render/Cargo.toml
@@ -20,5 +20,6 @@ ab_glyph = { workspace = true, optional = true }
 image = { version = "0.24", default-features = false, features = ["jpeg", "png", "webp"], optional = true }
 ureq = { version = "2.9", default-features = false, features = ["tls"], optional = true }
 base64 = { workspace = true, optional = true }
+cssparser = "0.34"
 [lib]
 path = "src/lib.rs"
diff --git a/crates/obscura-render/src/dom.rs b/crates/obscura-render/src/dom.rs
index c51ba75..eaf28fb 100644
--- a/crates/obscura-render/src/dom.rs
+++ b/crates/obscura-render/src/dom.rs
@@ -11,15 +11,57 @@ use std::collections::HashMap;
 use obscura_dom::tree::{DomTree, NodeId};
 use taffy::prelude::*;
 
-use crate::{compute_style, Rect, to_taffy_style};
+use crate::{Rect, to_taffy_style};
 
 /// Per-element border boxes after layout, in viewport coordinates.
 pub struct DomLayout {
     pub rects: HashMap<NodeId, Rect>,
+    pub styles: HashMap<NodeId, crate::LayoutStyle>,
 }
 
 /// Lay out a DOM tree within `viewport` (width, height) in CSS pixels.
 pub fn layout_dom(tree: &DomTree, viewport: (f32, f32)) -> DomLayout {
+    let mut css_rules = Vec::new();
+    for nid in tree.descendants(tree.document()) {
+        if let Some(node) = tree.get_node(nid) {
+            if let Some(elem) = node.as_element() {
+                if elem.local.as_ref() == "style" {
+                    let css = tree.text_content(nid);
+                    css_rules.extend(parse_simple_css(&css));
+                }
+            }
+        }
+    }
+
+    let mut styles: HashMap<NodeId, crate::LayoutStyle> = HashMap::new();
+    for nid in tree.descendants(tree.document()) {
+        if let Some(node) = tree.get_node(nid) {
+            if let Some(elem) = node.as_element() {
+                styles.insert(nid, crate::style::ua_style(elem.local.as_ref()));
+            }
+        }
+    }
+
+    for (selector, decls) in &css_rules {
+        if let Ok(matched) = tree.query_selector_all(selector) {
+            for nid in matched {
+                if let Some(style) = styles.get_mut(&nid) {
+                    crate::style::apply_inline(style, decls);
+                }
+            }
+        }
+    }
+
+    for nid in tree.descendants(tree.document()) {
+        if let Some(node) = tree.get_node(nid) {
+            if let Some(inline) = node.get_attribute("style") {
+                if let Some(style) = styles.get_mut(&nid) {
+                    crate::style::apply_inline(style, inline);
+                }
+            }
+        }
+    }
+
     let mut taffy_tree: TaffyTree = TaffyTree::new();
     let mut id_map: HashMap<taffy::NodeId, NodeId> = HashMap::new();
 
@@ -32,7 +74,7 @@ pub fn layout_dom(tree: &DomTree, viewport: (f32, f32)) -> DomLayout {
 
     let mut rects = HashMap::new();
     if let Some(root_id) = root {
-        if let Some(taffy_root) = build(tree, root_id, &mut taffy_tree, &mut id_map) {
+        if let Some(taffy_root) = build(tree, root_id, &mut taffy_tree, &mut id_map, &styles) {
             let _ = taffy_tree.compute_layout(
                 taffy_root,
                 taffy::Size {
@@ -55,7 +97,39 @@ pub fn layout_dom(tree: &DomTree, viewport: (f32, f32)) -> DomLayout {
             }
         }
     }
-    DomLayout { rects }
+    DomLayout { rects, styles }
+}
+
+fn parse_simple_css(css: &str) -> Vec<(String, String)> {
+    let mut rules = Vec::new();
+    let mut current_selector = String::new();
+    let mut current_decls = String::new();
+    let mut in_block = false;
+
+    for c in css.chars() {
+        if c == '{' && !in_block {
+            in_block = true;
+        } else if c == '}' && in_block {
+            in_block = false;
+            let sel = current_selector.trim();
+            let decls = current_decls.trim();
+            for s in sel.split(',') {
+                let s = s.trim();
+                if !s.is_empty() {
+                    rules.push((s.to_string(), decls.to_string()));
+                }
+            }
+            current_selector.clear();
+            current_decls.clear();
+        } else {
+            if in_block {
+                current_decls.push(c);
+            } else {
+                current_selector.push(c);
+            }
+        }
+    }
+    rules
 }
 
 fn build(
@@ -63,17 +137,17 @@ fn build(
     id: NodeId,
     taffy_tree: &mut TaffyTree,
     id_map: &mut HashMap<taffy::NodeId, NodeId>,
+    styles: &HashMap<NodeId, crate::LayoutStyle>,
 ) -> Option<taffy::NodeId> {
     let node = tree.get_node(id)?;
-    let name = node.as_element()?;
-    let tag = name.local.as_ref();
-    let style = compute_style(tag, node.get_attribute("style"));
-    let taffy_style = to_taffy_style(&style);
+    let _name = node.as_element()?;
+    let style = styles.get(&id)?;
+    let taffy_style = to_taffy_style(style);
 
     let child_ids: Vec<taffy::NodeId> = tree
         .children(id)
         .into_iter()
-        .filter_map(|cid| build(tree, cid, taffy_tree, id_map))
+        .filter_map(|cid| build(tree, cid, taffy_tree, id_map, styles))
         .collect();
 
     let taffy_id = if child_ids.is_empty() {
diff --git a/crates/obscura-render/src/paint.rs b/crates/obscura-render/src/paint.rs
index 7d098c0..bbc14f8 100644
--- a/crates/obscura-render/src/paint.rs
+++ b/crates/obscura-render/src/paint.rs
@@ -46,7 +46,10 @@ pub fn paint_dom(tree: &DomTree, viewport: (f32, f32)) -> Option<Pixmap> {
             None => continue,
         };
         
-        let style = crate::compute_style(name.local.as_ref(), node.get_attribute("style"));
+        let style = match laid.styles.get(&nid) {
+            Some(s) => s,
+            None => continue,
+        };
         
         if let Some(bg) = style.background_color {
             let mut path = PathBuilder::new();
@@ -119,12 +122,9 @@ fn paint_text_node(
     };
     
     // Find parent element to get geometry and color
-    let parent_id = node.parent?;
-    let parent = tree.get_node(parent_id)?;
-    let parent_name = parent.as_element()?;
-    
-    let rect = laid.rects.get(&parent_id)?;
-    let style = crate::compute_style(parent_name.local.as_ref(), parent.get_attribute("style"));
+    let parent = node.parent?;
+    let rect = laid.rects.get(&parent)?;
+    let style = laid.styles.get(&parent)?;
     // Default color to black if not specified.
     let color = style.color.unwrap_or([0, 0, 0, 255]);
     
diff --git a/crates/obscura-render/src/style.rs b/crates/obscura-render/src/style.rs
index d134ab9..3fd2f98 100644
--- a/crates/obscura-render/src/style.rs
+++ b/crates/obscura-render/src/style.rs
@@ -22,12 +22,12 @@ pub fn compute_style(tag: &str, inline_css: Option<&str>) -> LayoutStyle {
 
 /// Built-in UA defaults. Inline elements currently map to block layout; real
 /// inline/text layout arrives with the text/paint phase.
-fn ua_style(tag: &str) -> LayoutStyle {
+pub fn ua_style(tag: &str) -> LayoutStyle {
     let _ = tag;
     LayoutStyle { display: Display::Block, ..Default::default() }
 }
 
-fn apply_inline(style: &mut LayoutStyle, css: &str) {
+pub fn apply_inline(style: &mut LayoutStyle, css: &str) {
     for raw in css.split(';') {
         let decl = raw.trim();
         if decl.is_empty() {