Use a custom I-beam mouse cursor for pre-Mojave OS versions

Prevoiusly, #859 removed the custom high-contrast I-beam mouse cursor in
favor of using the system-default I-beam cursor. However, it mostly
worked well on 10.14 Mojave or above, as the cursor is designed with
dark mode in mind and works well on both bright and dark backgrounds.
Since this doesn't work well on older macOS versions, add back the
custom cursor and only enable it on those older macOS versions.

Fix #910.

src/MacVim/MMTextViewHelper.m

@@ -1028,6 +1028,38 @@ KeyboardInputSourcesEqual(TISInputSourceRef a, TISInputSourceRef b)
 
 - (void)setCursor
 {
+    static NSCursor *ibeamCursor = nil;
+
+    if (!ibeamCursor) {
+        if (floor(NSAppKitVersionNumber) >= NSAppKitVersionNumber10_14)
+        {
+            // macOS 10.14 (Mojave) introduced dark mode, and seems to have
+            // added a thick white border around the system I-beam cursor,
+            // which makes it legible across bright and dark background. Just
+            // use it.
+            ibeamCursor = [NSCursor IBeamCursor];
+        }
+        else
+        {
+            // Pre-Mojave versions the I-beam cursors doesn't have the strong
+            // white background and is hard to read on dark background. Use a
+            // custom I-beam cursor that has better contrast against dark
+            // backgrounds.
+            NSImage *ibeamImage = [NSImage imageNamed:@"ibeam"];
+            if (ibeamImage) {
+                NSSize size = [ibeamImage size];
+                NSPoint hotSpot = { size.width*.5f, size.height*.5f };
+                
+                ibeamCursor = [[NSCursor alloc]
+                               initWithImage:ibeamImage hotSpot:hotSpot];
+            }
+            if (!ibeamCursor) {
+                ASLogWarn(@"Failed to load custom Ibeam cursor");
+                ibeamCursor = [NSCursor IBeamCursor];
+            }
+        }
+    }
+
     // This switch should match mshape_names[] in misc2.c.
     //
     // We don't fill every shape here. Only the ones that make sense and have
@@ -1037,7 +1069,7 @@ KeyboardInputSourcesEqual(TISInputSourceRef a, TISInputSourceRef b)
             [[NSCursor arrowCursor] set]; break;
         //case 1: // blank
         case 2: // beam
-            [[NSCursor IBeamCursor] set]; break;
+            [ibeamCursor set]; break;
         case 3: // updown
         case 4: // udsizing
             [[NSCursor resizeUpDownCursor] set]; break;

src/MacVim/MacVim.h

@@ -48,6 +48,9 @@
 #ifndef NSAppKitVersionNumber10_13
 # define NSAppKitVersionNumber10_13 1561
 #endif
+#ifndef NSAppKitVersionNumber10_14
+# define NSAppKitVersionNumber10_14 1671
+#endif
 
 #if MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_12
 // Deprecated constants in 10.12 SDK

src/MacVim/MacVim.xcodeproj/project.pbxproj

@@ -53,6 +53,7 @@
 		1DCD00D30E50B2B700460166 /* Undo.png in Resources */ = {isa = PBXBuildFile; fileRef = 1DCD00BE0E50B2B700460166 /* Undo.png */; };
 		1DD04DEC0C529C5E006CDC2B /* Credits.rtf in Resources */ = {isa = PBXBuildFile; fileRef = 1DD04DEB0C529C5E006CDC2B /* Credits.rtf */; };
 		1DD0C20C0C60FFB4008CD84A /* gvimrc in Copy Vim Runtime Files */ = {isa = PBXBuildFile; fileRef = 1DD0C20A0C60FF9A008CD84A /* gvimrc */; };
+		1DD3D51E0D82D4C9006E4320 /* ibeam.png in Resources */ = {isa = PBXBuildFile; fileRef = 1DD3D51D0D82D4C9006E4320 /* ibeam.png */; };
 		1DD66ECE0C803D3600EBDAB3 /* MMApplication.m in Sources */ = {isa = PBXBuildFile; fileRef = 1DD66ECC0C803D3600EBDAB3 /* MMApplication.m */; };
 		1DD9F5E50C85D60500E8D5A5 /* SystemColors.plist in Resources */ = {isa = PBXBuildFile; fileRef = 1DD9F5E40C85D60500E8D5A5 /* SystemColors.plist */; };
 		1DE3F8E70D50F80500052B9E /* Preferences.nib in Resources */ = {isa = PBXBuildFile; fileRef = 1DE3F8E50D50F80500052B9E /* Preferences.nib */; };
@@ -228,6 +229,7 @@
 		1DCD00BE0E50B2B700460166 /* Undo.png */ = {isa = PBXFileReference; lastKnownFileType = image.png; name = Undo.png; path = Toolbar/Undo.png; sourceTree = "<group>"; };
 		1DD04DEB0C529C5E006CDC2B /* Credits.rtf */ = {isa = PBXFileReference; lastKnownFileType = text.rtf; path = Credits.rtf; sourceTree = "<group>"; };
 		1DD0C20A0C60FF9A008CD84A /* gvimrc */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text; path = gvimrc; sourceTree = "<group>"; };
+		1DD3D51D0D82D4C9006E4320 /* ibeam.png */ = {isa = PBXFileReference; lastKnownFileType = image.png; path = ibeam.png; sourceTree = "<group>"; };
 		1DD66ECB0C803D3600EBDAB3 /* MMApplication.h */ = {isa = PBXFileReference; fileEncoding = 30; lastKnownFileType = sourcecode.c.h; path = MMApplication.h; sourceTree = "<group>"; };
 		1DD66ECC0C803D3600EBDAB3 /* MMApplication.m */ = {isa = PBXFileReference; fileEncoding = 30; lastKnownFileType = sourcecode.c.objc; path = MMApplication.m; sourceTree = "<group>"; };
 		1DD9F5E40C85D60500E8D5A5 /* SystemColors.plist */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.plist.xml; path = SystemColors.plist; sourceTree = "<group>"; };
@@ -554,6 +556,7 @@
 				1D8BEA73104992290069B072 /* FindAndReplace.nib */,
 				0395A8A90D72D88B00881434 /* General.png */,
 				1D22374A0E45DF4800E6FFFF /* Advanced.png */,
+				1DD3D51D0D82D4C9006E4320 /* ibeam.png */,
 				1D0F11480D58C77800D5DA09 /* Font */,
 				1DE9726C0C48050600F96A9F /* Toolbar */,
 				1DD9F5E40C85D60500E8D5A5 /* SystemColors.plist */,
@@ -842,6 +845,7 @@
 				1DD9F5E50C85D60500E8D5A5 /* SystemColors.plist in Resources */,
 				1DE3F8E70D50F80500052B9E /* Preferences.nib in Resources */,
 				0395A8AA0D72D88B00881434 /* General.png in Resources */,
+				1DD3D51E0D82D4C9006E4320 /* ibeam.png in Resources */,
 				1D22374B0E45DF4800E6FFFF /* Advanced.png in Resources */,
 				1DCD00BF0E50B2B700460166 /* Attention.png in Resources */,
 				1DCD00C00E50B2B700460166 /* Copy.png in Resources */,