DragValue improvements (#274)

* Display ResizeHorizontal cursor on hover

* Adapt the URL open command to the platform

With this new version we use $OSTYPE bash env var to query what OS
are we running on.

- On Linux, ex: Fedora, we use `xdg-open`
- On Windows, ex: msys, we use `start`
- For other other variants we try to use `open`

We should update this script when we notice that `open` is not
available on a particular platform.

(cherry picked from commit b3aa4982f683d961c21fd18e9ffc1fdf5fba0783)

* Add slow speed mode for `DragValue`

The slow speed mode is disabled by default. It can be activated
or deactivated using `DragValue::slow_speed()`.

When active the `Shift` key can be used to have a better control
over the value, `DragValue::speed` / 10.0 increments.

* Display `ResizeHorizontal` cursor while dragging too

* Apply review suggestion

Shorter and in line with the rest of the code base

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

* Add `Modifiers::shift_only` for better code clarity

* Make slow speed always enabled

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

egui/src/data/input.rs

@@ -153,13 +153,20 @@ pub struct Modifiers {
 }
 
 impl Modifiers {
+    #[inline(always)]
     pub fn is_none(&self) -> bool {
         self == &Self::default()
     }
 
+    #[inline(always)]
     pub fn any(&self) -> bool {
         !self.is_none()
     }
+
+    #[inline(always)]
+    pub fn shift_only(&self) -> bool {
+        self.shift && !(self.alt || self.command)
+    }
 }
 
 /// Keyboard keys.

egui/src/widgets/drag_value.rs

@@ -217,10 +217,15 @@ impl<'a> Widget for DragValue<'a> {
             max_decimals,
         } = self;
 
+        let is_slow_speed = ui.input().modifiers.shift_only();
+
         let value = get(&mut get_set_value);
         let value = clamp_to_range(value, clamp_range.clone());
         let aim_rad = ui.input().aim_radius() as f64;
+
         let auto_decimals = (aim_rad / speed.abs()).log10().ceil().clamp(0.0, 15.0) as usize;
+        let auto_decimals = auto_decimals + is_slow_speed as usize;
+
         let max_decimals = max_decimals.unwrap_or(auto_decimals + 2);
         let auto_decimals = auto_decimals.clamp(min_decimals, max_decimals);
         let value_text = if value == 0.0 {
@@ -262,21 +267,30 @@ impl<'a> Widget for DragValue<'a> {
                 .sense(Sense::click_and_drag())
                 .text_style(TextStyle::Monospace)
                 .wrap(false);
+
             let response = ui.add_sized(ui.spacing().interact_size, button);
-            let response = response.on_hover_text(format!(
-                "{}{}{}\nDrag to edit or click to enter a value.",
-                prefix,
-                value as f32, // Show full precision value on-hover. TODO: figure out f64 vs f32
-                suffix
-            ));
+            let response = response
+                .on_hover_cursor(CursorIcon::ResizeHorizontal)
+                .on_hover_text(format!(
+                    "{}{}{}\nDrag to edit or click to enter a value.\nPress 'Shift' while dragging for better control.",
+                    prefix,
+                    value as f32, // Show full precision value on-hover. TODO: figure out f64 vs f32
+                    suffix
+                ));
 
             if response.clicked() {
                 ui.memory().request_focus(kb_edit_id);
                 ui.memory().drag_value.edit_string = None; // Filled in next frame
             } else if response.dragged() {
+                ui.output().cursor_icon = CursorIcon::ResizeHorizontal;
+
                 let mdelta = response.drag_delta();
                 let delta_points = mdelta.x - mdelta.y; // Increase to the right and up
+
+                let speed = if is_slow_speed { speed / 10.0 } else { speed };
+
                 let delta_value = delta_points as f64 * speed;
+
                 if delta_value != 0.0 {
                     let mut drag_state = std::mem::take(&mut ui.memory().drag_value);