Make it easier to grab the handle of a floating scroll bar (#4754)

Should solve https://github.com/rerun-io/rerun/issues/6700

crates/egui/src/containers/scroll_area.rs

@@ -966,17 +966,22 @@ impl Prepared {
             // top/bottom of a horizontal scroll (d==0).
             // left/rigth of a vertical scroll (d==1).
             let mut cross = if scroll_style.floating {
+                // The bounding rect of a fully visible bar.
+                // When we hover this area, we should show the full bar:
                 let max_bar_rect = if d == 0 {
-                    outer_rect.with_min_y(outer_rect.max.y - scroll_style.allocated_width())
+                    outer_rect.with_min_y(outer_rect.max.y - outer_margin - scroll_style.bar_width)
                 } else {
-                    outer_rect.with_min_x(outer_rect.max.x - scroll_style.allocated_width())
+                    outer_rect.with_min_x(outer_rect.max.x - outer_margin - scroll_style.bar_width)
                 };
+
                 let is_hovering_bar_area = is_hovering_outer_rect
                     && ui.rect_contains_pointer(max_bar_rect)
                     || state.scroll_bar_interaction[d];
+
                 let is_hovering_bar_area_t = ui
                     .ctx()
                     .animate_bool_responsive(id.with((d, "bar_hover")), is_hovering_bar_area);
+
                 let width = show_factor
                     * lerp(
                         scroll_style.floating_width..=scroll_style.bar_width,

crates/egui/src/style.rs

@@ -1163,9 +1163,9 @@ impl Default for Spacing {
 impl Default for Interaction {
     fn default() -> Self {
         Self {
+            interact_radius: 5.0,
             resize_grab_radius_side: 5.0,
             resize_grab_radius_corner: 10.0,
-            interact_radius: 5.0,
             show_tooltips_only_when_still: true,
             tooltip_delay: 0.5,
             tooltip_grace_time: 0.2,