Misc. inline box layout fixes (#207)

See individual commits:

- Fix whitespace collapsing when first item in a span is an inline box
- `<p><img src="..." /> label</p>` *should* have a space between the
image and "label".
- Fix wrapping when layout contains only inline boxes
- Test case for layout with only inline boxes
- Prevent inline boxes from being duplicated when the line ends with an
inline box.
- Fix trailing whitespace computation:
- If the last item on a line is an inline box, then it does not have any
trailing whitespace.

---------

Signed-off-by: Nico Burns <[email protected]>

parley/src/builder.rs

@@ -101,6 +101,7 @@ impl<B: Brush> TreeBuilder<'_, B> {
 
     pub fn push_inline_box(&mut self, mut inline_box: InlineBox) {
         self.lcx.tree_style_builder.push_uncommitted_text(false);
+        self.lcx.tree_style_builder.set_is_span_first(false);
         // TODO: arrange type better here to factor out the index
         inline_box.index = self.lcx.tree_style_builder.current_text_len();
         self.lcx.inline_boxes.push(inline_box);

parley/src/layout/line/greedy.rs

@@ -149,11 +149,12 @@ impl<'a, B: Brush> BreakLines<'a, B> {
 
         // HACK: ignore max_advance for empty layouts
         // Prevents crash when width is too small (https://github.com/linebender/parley/issues/186)
-        let max_advance = if self.layout.data.text_len == 0 {
-            f32::MAX
-        } else {
-            max_advance
-        };
+        let max_advance =
+            if self.layout.data.text_len == 0 && self.layout.data.inline_boxes.is_empty() {
+                f32::MAX
+            } else {
+                max_advance
+            };
 
         // This macro simply calls the `commit_line` with the provided arguments and some parts of self.
         // It exists solely to cut down on the boilerplate for accessing the self variables while
@@ -528,14 +529,10 @@ impl<'a, B: Brush> BreakLines<'a, B> {
             line.metrics.trailing_whitespace = 0.0;
             if !line.item_range.is_empty() {
                 // Note: there may not be a "last run" if there are no runs in the line
-                let last_run = &self
-                    .lines
-                    .line_items
-                    .iter()
-                    .rfind(|item| item.is_text_run());
-                if let Some(last_run) = last_run {
-                    if !last_run.cluster_range.is_empty() {
-                        let cluster = &self.layout.data.clusters[last_run.cluster_range.end - 1];
+                let last_item = &self.lines.line_items.last();
+                if let Some(last_item) = last_item {
+                    if last_item.is_text_run() && !last_item.cluster_range.is_empty() {
+                        let cluster = &self.layout.data.clusters[last_item.cluster_range.end - 1];
                         if cluster.info.whitespace().is_space_or_nbsp() {
                             line.metrics.trailing_whitespace = cluster.advance;
                         }
@@ -726,6 +723,7 @@ fn try_commit_line<B: Brush>(
 
     // Iterate over the items to commit
     // println!("\nCOMMIT LINE");
+    let mut last_item_kind = LayoutItemKind::TextRun;
     for (i, item) in items_to_commit.iter().enumerate() {
         // println!("i = {} index = {} {:?}", i, item.index, item.kind);
 
@@ -745,6 +743,8 @@ fn try_commit_line<B: Brush>(
                     cluster_range: 0..0,
                     text_range: 0..0,
                 });
+
+                last_item_kind = item.kind;
             }
             LayoutItemKind::TextRun => {
                 let run_data = &layout.data.runs[item.index];
@@ -768,6 +768,8 @@ fn try_commit_line<B: Brush>(
                     continue;
                 }
 
+                last_item_kind = item.kind;
+
                 // Push run to line
                 let run = Run::new(layout, 0, 0, run_data, None);
                 let text_range = if run_data.cluster_range.is_empty() {
@@ -825,10 +827,21 @@ fn try_commit_line<B: Brush>(
     });
 
     // Reset state for the new line
+    state.num_spaces = 0;
     state.clusters.start = state.clusters.end;
     state.clusters.end += 1;
-    state.items.start = state.items.end.saturating_sub(1);
-    state.num_spaces = 0;
+
+    state.items.start = match last_item_kind {
+        // For text runs, the first item of line N+1 needs to be the SAME as
+        // the last item for line N. This is because the item (if it a text run
+        // may be split across the two lines with some clusters in line N and some
+        // in line N+1). The item is later filtered out (see `continue` in loop above)
+        // if there are not actually any clusters in line N+1.
+        LayoutItemKind::TextRun => state.items.end.saturating_sub(1),
+        // Inline boxes cannot be spread across multiple lines, so we should set
+        // the first item of line N+1 to be the item AFTER the last item in line N.
+        LayoutItemKind::InlineBox => state.items.end,
+    };
 
     true
 }

parley/src/resolve/tree.rs

@@ -68,6 +68,10 @@ impl<B: Brush> TreeStyleBuilder<B> {
         self.white_space_collapse = white_space_collapse;
     }
 
+    pub(crate) fn set_is_span_first(&mut self, is_span_first: bool) {
+        self.is_span_first = is_span_first;
+    }
+
     pub(crate) fn push_uncommitted_text(&mut self, is_span_last: bool) {
         let span_text: Cow<'_, str> = match self.white_space_collapse {
             WhiteSpaceCollapse::Preserve => Cow::from(&self.uncommitted_text),
@@ -109,6 +113,7 @@ impl<B: Brush> TreeStyleBuilder<B> {
 
         // Nothing to do if there is no uncommitted text.
         if span_text.is_empty() {
+            self.uncommitted_text.clear();
             return;
         }
 

parley/src/tests/test_basic.rs

@@ -40,3 +40,24 @@ fn placing_inboxes() {
         env.with_name(test_case_name).check_layout_snapshot(&layout);
     }
 }
+
+#[test]
+fn only_inboxes_wrap() {
+    let mut env = testenv!();
+
+    let text = "";
+    let mut builder = env.builder(text);
+    for id in 0..10 {
+        builder.push_inline_box(InlineBox {
+            id,
+            index: 0,
+            width: 10.0,
+            height: 10.0,
+        });
+    }
+    let mut layout = builder.build(text);
+    layout.break_all_lines(Some(40.0));
+    layout.align(None, Alignment::Middle);
+
+    env.check_layout_snapshot(&layout);
+}