Fix scrollbar markers in large files (#10181)

Andrew Lygin created 2 years ago

#10080 introduced a minor change in how the min marker height is
enforced. Before the change, it was applied to the aggregated marker,
but after the change it's applied to each individual marker before
aggregation.

The difference is not noticeable on small files, where even single row
markers are higher than `MIN_MARKER_HEIGHT`, but it leads to visible
differences in large files with repeating blocks of highlighted and
not-highlighted blocks, like in [this
case](https://github.com/zed-industries/zed/pull/9080#issuecomment-2006796376).

This PR fixes how the `MIN_MARKER_HEIGHT` is applied.

Before the fix:

<img width="727" alt="zed-scroll-markers-before"
src="https://github.com/zed-industries/zed/assets/2101250/a1c34746-af4f-4054-8de2-edabf3db7cee">

After the fix:

<img width="736" alt="zed-scroll-markers-after"
src="https://github.com/zed-industries/zed/assets/2101250/b9ee843d-055e-42a6-af26-e7fd4f7729f8">


Release Notes:

- N/A

/cc @mrnugget

Change summary

crates/editor/src/element.rs | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

Detailed changes

crates/editor/src/element.rs

@@ -3875,10 +3875,7 @@ impl ScrollbarLayout {
             .into_iter()
             .map(|range| {
                 let start_y = self.first_row_y_offset + range.start as f32 * self.row_height;
-                let mut end_y = self.first_row_y_offset + (range.end + 1) as f32 * self.row_height;
-                if end_y - start_y < Self::MIN_MARKER_HEIGHT {
-                    end_y = start_y + Self::MIN_MARKER_HEIGHT;
-                }
+                let end_y = self.first_row_y_offset + (range.end + 1) as f32 * self.row_height;
                 ColoredRange {
                     start: start_y,
                     end: end_y,
@@ -3889,11 +3886,14 @@ impl ScrollbarLayout {
 
         let mut quads = Vec::new();
         while let Some(mut pixel_range) = background_pixel_ranges.next() {
+            pixel_range.end = pixel_range
+                .end
+                .max(pixel_range.start + Self::MIN_MARKER_HEIGHT);
             while let Some(next_pixel_range) = background_pixel_ranges.peek() {
                 if pixel_range.end >= next_pixel_range.start
                     && pixel_range.color == next_pixel_range.color
                 {
-                    pixel_range.end = next_pixel_range.end;
+                    pixel_range.end = next_pixel_range.end.max(pixel_range.end);
                     background_pixel_ranges.next();
                 } else {
                     break;