zoom: a magnifier cursor (zoom-in), a grabbing hand while dragging

docs/test-checklist.md

@@ -54,6 +54,7 @@ image, a cancel brought the thumbnail back, and a swipe still dismissed it.
 ## Zoom (Phase 4)
 
 - [ ] `valw zoom` → the focused output freezes at 1×; Esc and `q` leave, nothing saved, exit 0, thumbnails come back.
+- [ ] The pointer is a magnifier (zoom-in) over the zoom, a grabbing hand while dragging, the magnifier again after.
 - [ ] Wheel zooms towards the pointer (the point under it stays put), smoothly, up to 32×; pixels stay crisp.
 - [ ] Touchpad scrolling zooms smoothly too.
 - [ ] Left drag pans 1:1 and never shows anything outside the screenshot; the cursor turns into a grabbing hand.

src/zoom/mod.rs

@@ -238,8 +238,8 @@ impl Zoom {
             let p = (event.position.0 * self.ratio, event.position.1 * self.ratio);
             match event.kind {
                 PointerEventKind::Enter { serial } => {
-                    if let Some(cursor) = cursor {
-                        cursor.set_shape(serial, Shape::Default);
+                    if let Some(device) = cursor {
+                        device.set_shape(serial, self::cursor(self.panning.is_some()));
                     }
                     self.pointer = p;
                 }
@@ -249,8 +249,8 @@ impl Zoom {
                     ..
                 } => {
                     self.panning = Some(p);
-                    if let Some(cursor) = cursor {
-                        cursor.set_shape(serial, Shape::Grabbing);
+                    if let Some(device) = cursor {
+                        device.set_shape(serial, self::cursor(true));
                     }
                 }
                 PointerEventKind::Release {
@@ -259,8 +259,8 @@ impl Zoom {
                     ..
                 } => {
                     self.panning = None;
-                    if let Some(cursor) = cursor {
-                        cursor.set_shape(serial, Shape::Default);
+                    if let Some(device) = cursor {
+                        device.set_shape(serial, self::cursor(false));
                     }
                 }
                 PointerEventKind::Motion { .. } => {
@@ -320,10 +320,26 @@ impl Zoom {
     }
 }
 
+/// The pointer over a zoom: a magnifier, so it reads as zoom mode, and a
+/// grabbing hand while dragging the view.
+fn cursor(panning: bool) -> Shape {
+    if panning {
+        Shape::Grabbing
+    } else {
+        Shape::ZoomIn
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
 
+    #[test]
+    fn the_cursor_says_zoom_and_grabs_while_dragging() {
+        assert_eq!(cursor(false), Shape::ZoomIn);
+        assert_eq!(cursor(true), Shape::Grabbing);
+    }
+
     #[test]
     fn keys() {
         assert_eq!(command(Keysym::Escape), Some(Command::Leave));