fix: distinguish grab and grabbing cursors (#1154)

On macOS, there is a difference between a "grab" cursor and a "grabbing"
cursor, where "grab" is an open-hand cursor used during a hover, and
"grabbing" is a closed-hand cursor used on a click. These, and other
native MacOS cursors, can be seen at the [NSCursor documentation](https://developer.apple.com/documentation/appkit/nscursor?language=objc).

See https://github.com/hecrj/iced/issues/9 for the motivation for this
PR.

CHANGELOG.md

@@ -6,6 +6,7 @@
 - On iOS, fix improper `msg_send` usage that was UB and/or would break if `!` is stabilized.
 - On Windows, unset `maximized` when manually changing the window's position or size.
 - On Windows, add touch pressure information for touch events.
+- On macOS, differentiate between `CursorIcon::Grab` and `CursorIcon::Grabbing`.
 - On Wayland, fix event processing sometimes stalling when using OpenGL with vsync.
 
 # 0.20.0 Alpha 3 (2019-08-14)

src/platform_impl/macos/util/cursor.rs

@@ -15,10 +15,12 @@ pub enum Cursor {
 
 impl From<CursorIcon> for Cursor {
     fn from(cursor: CursorIcon) -> Self {
+        // See native cursors at https://developer.apple.com/documentation/appkit/nscursor?language=objc.
         match cursor {
             CursorIcon::Arrow | CursorIcon::Default => Cursor::Native("arrowCursor"),
             CursorIcon::Hand => Cursor::Native("pointingHandCursor"),
-            CursorIcon::Grabbing | CursorIcon::Grab => Cursor::Native("closedHandCursor"),
+            CursorIcon::Grab => Cursor::Native("openHandCursor"),
+            CursorIcon::Grabbing => Cursor::Native("closedHandCursor"),
             CursorIcon::Text => Cursor::Native("IBeamCursor"),
             CursorIcon::VerticalText => Cursor::Native("IBeamCursorForVerticalLayout"),
             CursorIcon::Copy => Cursor::Native("dragCopyCursor"),

src/window.rs

@@ -760,7 +760,9 @@ pub enum CursorIcon {
     Alias,
     Copy,
     NoDrop,
+    /// Indicates something can be grabbed.
     Grab,
+    /// Indicates something is grabbed.
     Grabbing,
     AllScroll,
     ZoomIn,