Fix 10.12 transparent title bar, and 10.14 'transparency' issues

Change the code that sets window's backgroundColor to Mojave (10.14)
only. Right now, we are creating windows with the flag
NSWindowStyleMaskTexturedBackground which is actually deprecated, and it
had the annoying effect of auto-setting transparent title bars in Sierra
SDKs. When the previous change set the background color of the window it
also made the title bar color change as well. Now, the background color
is only set for Mojave so those earlier platforms won't be affected.

Also fix the 'transparency' setting in Mojave. Since in Mojave the
rendering is done through layers now, we need to make sure the layers
are all transparent other than the text view that's trying to blend on
top of the desktop (this is why we needed to set the window background
color to begin with). There *is* one hack where we have to set the
window background with 0.001 alpha because if you set to 0, the whole
border disappears the the window behaves sluggishly.

In the future, consider removing NSWindowStyleMaskTexturedBackground
since it's been deprecated for a while. One issue is that without it the
system title bar has this annoying gray/black line and it doesn't look
as neat. It's a minor aesthetics issue though and if in the future it
gets completely deprecated it's not a big deal. Alternatively, consider
using a transparent title bar and use customized theming.

Also, fix a regression where zoom button was not working properly in
pre-Mojave, due to [NSAnimationContext beginGrouping] being improperly
called.

Fix #799.

src/MacVim/MMBackend.m

@@ -1187,7 +1187,7 @@ extern GuiFont gui_mch_retain_font(GuiFont font);
 {
     NSMutableData *data = [NSMutableData data];
     [data appendBytes:&fuoptions length:sizeof(int)];
-    bg = MM_COLOR(bg);
+    bg = MM_COLOR_WITH_TRANSP(bg,p_transp);
     [data appendBytes:&bg length:sizeof(int)];
     [self queueMessage:EnterFullScreenMsgID data:data];
 }

src/MacVim/MMCoreTextView.m

@@ -452,7 +452,7 @@ defaultAdvanceForFont(NSFont *font)
 
 - (void)setFrameSize:(NSSize)newSize {
     if (!NSEqualSizes(newSize, self.bounds.size)) {
-        if (!drawPending && !cgBufferDrawEnabled) {
+        if (!drawPending && !cgBufferDrawEnabled && drawData.count == 0) {
             // When resizing a window, it will invalidate the buffer and cause
             // MacVim to draw black until we get the draw commands from Vim and
             // we draw them out in drawRect. Use beginGrouping to stop the

src/MacVim/MMVimView.m

@@ -497,14 +497,12 @@ enum {
 
     CALayer *backedLayer = [self layer];
     if (backedLayer) {
-        // This would only trigger in 10.14 where all views are layer-backed.
-        //
-        // Note: This doesn't do much now. Should fix this class to use
-        // updateLayer: instead of drawRect: at a later time, which would draw
-        // the background color automatically. When we do that we can remove the
-        // hack at drawKnobSlotInRect: since it would overlay properly without
-        // needing to manually draw the background color itself.
-        [backedLayer setBackgroundColor:[back CGColor]];
+        // This only happens in 10.14+, where everything is layer-backed by
+        // default. Since textView draws itself as a separate layer, we don't
+        // want this layer to draw anything. This is especially important with
+        // 'transparency' where there's alpha blending and we don't want this
+        // layer to be in the way and double-blending things.
+        [backedLayer setBackgroundColor:CGColorGetConstantColor(kCGColorClear)];
     }
 
     for (NSUInteger i = 0, count = [scrollbars count]; i < count; ++i) {
@@ -1005,10 +1003,10 @@ enum {
     // show through rendering artifacts (e.g. if guioption 'k' is on, and you
     // turn off the bar bar, the artiacts will show through in the overlay).
     //
-    // Note: This should ideally be done on MMVimView itself by setting a background
-    // color. This would be fixed at a later time by telling the view to just
-    // use the background color form the backed CALayer (mandated since Mojave
-    // 10.14).
+    // Note: Another way to fix this is to make sure to draw the underlying
+    // MMVimView or the window with the proper color so the scrollbar would just
+    // draw on top, but this doesn't work properly right now, and it's difficult
+    // to get that to work with the 'transparency' setting as well.
     MMVimView *vimView = [self target];
     NSColor *defaultBackgroundColor = [[vimView textView] defaultBackgroundColor];
     [defaultBackgroundColor setFill];

src/MacVim/MMWindowController.m

@@ -543,7 +543,39 @@
     [decoratedWindow setOpaque:isOpaque];
     if (fullScreenWindow)
         [fullScreenWindow setOpaque:isOpaque];
-    [decoratedWindow setBackgroundColor:back];
+
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_14
+    if (@available(macos 10.14, *)) {
+        // We usually don't really need to change the background color of the
+        // window, but in 10.14+ we switched to using layer-backed drawing.
+        // That's fine except when we set 'transparency' to non-zero. The alpha
+        // is set on the text view, but it won't work if drawn on top of a solid
+        // window, so we need to set a transparency color here to make the
+        // transparency show through.
+        if ([back alphaComponent] == 1) {
+            // Here, any solid color would do, but setting it with "back" has an
+            // interesting effect where the title bar gets subtly tinted by it
+            // as well, so do that. (Note that this won't play well in <=10.12
+            // since we are using the deprecated
+            // NSWindowStyleMaskTexturedBackground which makes the titlebars
+            // transparent in those. Consider not using textured background.)
+            [decoratedWindow setBackgroundColor:back];
+            if (fullScreenWindow) {
+                [fullScreenWindow setBackgroundColor:back];
+            }
+        } else {
+            // HACK! We really want a transparent background color to avoid
+            // double blending the transparency, but setting alpha=0 leads to
+            // the window border disappearing and also drag-to-resize becomes a
+            // lot slower. So hack around it by making it virtually transparent.
+            NSColor *clearColor = [back colorWithAlphaComponent:0.001];
+            [decoratedWindow setBackgroundColor:clearColor];
+            if (fullScreenWindow) {
+                [fullScreenWindow setBackgroundColor:clearColor];
+            }
+        }
+    }
+#endif
 
     [vimView setDefaultColorsBackground:back foreground:fore];
 }
@@ -758,8 +790,16 @@
         // times during startup.
         [fullScreenWindow release];
 
+        NSColor *fullscreenBg = back;
+
+        // See setDefaultColorsBackground: for why set a transparent
+        // background color, and why 0.001 instead of 0.
+        if ([fullscreenBg alphaComponent] != 1) {
+            fullscreenBg = [fullscreenBg colorWithAlphaComponent:0.001];
+        }
+
         fullScreenWindow = [[MMFullScreenWindow alloc]
-            initWithWindow:decoratedWindow view:vimView backgroundColor:back];
+            initWithWindow:decoratedWindow view:vimView backgroundColor:fullscreenBg];
         [fullScreenWindow setOptions:fuoptions];
         [fullScreenWindow setRepresentedFilename:
             [decoratedWindow representedFilename]];
@@ -1544,7 +1584,7 @@
     BOOL windowTextured = ([decoratedWindow styleMask] &
                             NSWindowStyleMaskTexturedBackground) != 0;
     BOOL hideSeparator  = NO;
-    
+
     if (floor(NSAppKitVersionNumber) >= NSAppKitVersionNumber10_10) {
         // The tabline separator is mostly an old feature and not necessary
         // modern macOS versions.