Make the Core Text renderer faster

This change reworks `MMCoreTextView` to keep track of the state of the
screen instead of drawing to the screen or to an image. This lets
`drawRect:` draw any part of the view at any time, as needed.

This change came about when the old strategy stopped working: The old
strategy calls `drawRect:` for the entire view to handle any draw
command from the backend, but drew only the changes on top of the old
content of the view. This did not work in new versions of macOS that use
layers, because `drawRect:` is now expected to fill the entire rect with
new content. If it doesn't, the rest of the view will just contain
garbage. bbad3ed worked around this
issue by adding an intermediate CGImage which was preserved between
draws. This fixed the problem but made rendering slower.

With the change, the intermediate image is no longer needed and
rendering is much faster overall, which resolves #796.

As part of this change, font substitution is now handled by Core Text,
which changes which fallback fonts are used in some cases but matches
other macOS apps.

Author: s4y

src/MacVim/MMAppController.m

@@ -248,8 +248,6 @@ + (void)initialize
         [NSNumber numberWithBool:NO],     MMSuppressTerminationAlertKey,
         [NSNumber numberWithBool:YES],    MMNativeFullScreenKey,
         [NSNumber numberWithDouble:0.25], MMFullScreenFadeTimeKey,
-        [NSNumber numberWithBool:NO],     MMUseCGLayerAlwaysKey,
-        @(shouldUseBufferedDrawing()),    MMBufferedDrawingKey,
         [NSNumber numberWithBool:YES],    MMShareFindPboardKey,
         nil];
 

src/MacVim/MMCoreTextView.h

@@ -31,42 +31,13 @@
     BOOL                        antialias;
     BOOL                        ligatures;
     BOOL                        thinStrokes;
-    BOOL                        drawPending;
-    NSMutableArray              *drawData;
 
     MMTextViewHelper            *helper;
 
-    unsigned                    maxlen;
-    CGGlyph                     *glyphs;
-    CGPoint                     *positions;
-    NSMutableArray              *fontCache;
-
-    // Issue draws onto an CGImage that caches the drawn results instead of
-    // directly in drawRect:. This is the default behavior in cases where simply
-    // drawing incrementally in drawRect: doesn't work. Those cases are:
-    // 1. Non-native fullscreen
-    // 2. 10.14+ (views are always layer-backed which means the view buffer will
-    //    be cleared and we can't incrementally draw in drawRect:)
-    //    
-    // This can be configured by setting MMBufferedDrawingKey in user defaults.
-    BOOL                        cgBufferDrawEnabled;
-    BOOL                        cgBufferDrawNeedsUpdateContext;
-    CGContextRef                cgContext;
+    NSMutableDictionary<NSNumber *, NSFont *> *fontVariants;
+    NSMutableSet<NSString *> *characterStrings;
+    NSMutableDictionary<NSNumber *,NSCache<NSString *,id> *> *characterLines;
 
-    // *Deprecated*
-    // Draw onto a CGLayer instead of lazily updating the view's buffer in
-    // drawRect: which is error-prone and relying on undocumented behaviors
-    // (that the OS will preserve the old buffer).
-    //
-    // This is deprecated. Use cgBufferDrawEnabled instead which is more
-    // efficient.
-    //    
-    // This can be configured by setting MMUseCGLayerAlwaysKey in user defaults.
-    BOOL                        cgLayerEnabled;
-    CGLayerRef                  cgLayer;
-    CGContextRef                cgLayerContext;
-    NSLock                      *cgLayerLock;
-
     // These are used in MMCoreTextView+ToolTip.m
     id trackingRectOwner_;              // (not retained)
     void *trackingRectUserData_;
@@ -113,13 +84,10 @@
 - (BOOL)convertPoint:(NSPoint)point toRow:(int *)row column:(int *)column;
 - (NSRect)rectForRow:(int)row column:(int)column numRows:(int)nr
           numColumns:(int)nc;
-- (void)setCGLayerEnabled:(BOOL)enabled;
-- (BOOL)getCGLayerEnabled;
 
 //
 // NSTextView methods
 //
-- (void)setFrameSize:(NSSize)newSize;
 - (void)keyDown:(NSEvent *)event;
 - (void)insertText:(id)string;
 - (void)doCommandBySelector:(SEL)selector;