Mojave workarounds from dosbox-x:
https://github.com/joncampbell123/dosbox-x/commit/fdf6061c05dcb35a1ea111ad5b75ade350059df3
https://github.com/joncampbell123/dosbox-x/commit/347ffff35507177a2004a62e28493126d5f4dc81
https://github.com/joncampbell123/dosbox-x/commit/53e3ab2306ba2f2724ca3cb9f2c27608313c1ea5
https://github.com/joncampbell123/dosbox-x/commit/2c683142151171ba28a603b0724b6663bcd8ed98

diff --git a/src/video/quartz/SDL_QuartzVideo.m b/src/video/quartz/SDL_QuartzVideo.m
--- a/src/video/quartz/SDL_QuartzVideo.m
+++ b/src/video/quartz/SDL_QuartzVideo.m
@@ -938,10 +938,14 @@ static SDL_Surface* QZ_SetVideoFullScree
     mode_flags = current->flags;
 
     /* Set app state, hide cursor if necessary, ... */
     QZ_DoActivate(this);
 
+    [ window_view setNeedsDisplay:YES ];
+    [ [ qz_window contentView ] setNeedsDisplay:YES ];
+    [ qz_window displayIfNeeded ];
+
     return current;
 
     /* Since the blanking window covers *all* windows (even force quit) correct recovery is crucial */
 ERR_NO_GL:      goto ERR_DOUBLEBUF;  /* this goto is to stop a compiler warning on newer SDKs. */
 ERR_DOUBLEBUF:  QZ_RestoreDisplayMode(this);
@@ -1114,10 +1118,14 @@ static SDL_Surface* QZ_SetVideoWindowed 
     }
 
     /* Save flags to ensure correct teardown */
     mode_flags = current->flags;
 
+    [ window_view setNeedsDisplay:YES ];
+    [ [ qz_window contentView ] setNeedsDisplay:YES ];
+    [ qz_window displayIfNeeded ];
+
     /* Fade in again (asynchronously) if we came from a fullscreen mode and faded to black */
     if (fade_token != kCGDisplayFadeReservationInvalidToken) {
         CGDisplayFade (fade_token, 0.5, kCGDisplayBlendSolidColor, kCGDisplayBlendNormal, 0.0, 0.0, 0.0, FALSE);
         CGReleaseDisplayFadeReservation (fade_token);
     }
@@ -1153,11 +1161,17 @@ static SDL_Surface* QZ_SetVideoModeInter
             return NULL;
     }
 
     if (qz_window != nil) {
         nsgfx_context = [NSGraphicsContext graphicsContextWithWindow:qz_window];
-        [NSGraphicsContext setCurrentContext:nsgfx_context];
+        if (nsgfx_context != NULL) {
+            [NSGraphicsContext setCurrentContext:nsgfx_context];
+        }
+        else {
+            /* Whoops, looks like Mojave doesn't support this anymore */
+            fprintf(stderr,"Unable to obtain graphics context for NSWindow (Mojave behavior)\n");
+        }
     }
 
     /* Setup the new pixel format */
     {
         int amask = 0,
@@ -1498,23 +1512,32 @@ static void QZ_DrawResizeIcon (_THIS)
             
         SDL_BlitSurface (resize_icon, NULL, SDL_VideoSurface, &icon_rect);
     }
 }
 
-static void QZ_UpdateRects (_THIS, int numRects, SDL_Rect *rects)
+static SDL_VideoDevice *last_this = NULL;
+
+void QZ_UpdateRectsOnDrawRect (/*TODO: NSRect from drawRect*/)
 {
+    SDL_VideoDevice *this = last_this; /* HACK */
+
+    if (this == NULL) return;
+    if (SDL_VideoSurface == NULL)
+        return;
+
     if (SDL_VideoSurface->flags & SDL_OPENGLBLIT) {
-        QZ_GL_SwapBuffers (this);
+        /* TODO? */
     }
     else if ( [ qz_window isMiniaturized ] ) {
     
         /* Do nothing if miniaturized */
     }
     
     else {
         NSGraphicsContext *ctx = [NSGraphicsContext currentContext];
+        /* NTS: nsgfx_context == NULL will occur on Mojave, may be non-NULL on older versions of OS X */
-        if (ctx != nsgfx_context) { /* uhoh, you might be rendering from another thread... */
+        if (nsgfx_context != NULL && ctx != nsgfx_context) { /* uhoh, you might be rendering from another thread... */
             [NSGraphicsContext setCurrentContext:nsgfx_context];
             ctx = nsgfx_context;
         }
         CGContextRef cgc = (CGContextRef) [ctx graphicsPort];
         QZ_DrawResizeIcon (this);
@@ -1526,10 +1549,28 @@ static void QZ_UpdateRects (_THIS, int n
         CGImageRelease(image);
         CGContextFlush (cgc);
     }
 }
 
+static void QZ_UpdateRects (_THIS, int numRects, SDL_Rect *rects)
+{
+    last_this = this; /* HACK */
+
+    if (SDL_VideoSurface->flags & SDL_OPENGLBLIT) {
+        QZ_GL_SwapBuffers (this);
+        /* TODO? */
+    }
+    else if ( [ qz_window isMiniaturized ] ) {
+        /* Do nothing if miniaturized */
+    }
+    else {
+        [ window_view setNeedsDisplay:YES ];
+        [ [ qz_window contentView ] setNeedsDisplay:YES ];
+        [ qz_window displayIfNeeded ];
+    }
+}
+
 static void QZ_VideoQuit (_THIS)
 {
     CGDisplayFadeReservationToken fade_token = kCGDisplayFadeReservationInvalidToken;
 
     /* Restore gamma settings */
diff --git a/src/video/quartz/SDL_QuartzWindow.h b/src/video/quartz/SDL_QuartzWindow.h
--- a/src/video/quartz/SDL_QuartzWindow.h
+++ b/src/video/quartz/SDL_QuartzWindow.h
@@ -45,7 +45,8 @@ typedef unsigned int NSUInteger;
 - (BOOL)windowShouldClose:(id)sender;
 @end
 
 /* Subclass of NSView to set cursor rectangle */
 @interface SDL_QuartzView : NSView
+- (void)drawRect:(NSRect)dirtyRect;
 - (void)resetCursorRects;
 @end
diff --git a/src/video/quartz/SDL_QuartzWindow.m b/src/video/quartz/SDL_QuartzWindow.m
--- a/src/video/quartz/SDL_QuartzWindow.m
+++ b/src/video/quartz/SDL_QuartzWindow.m
@@ -218,10 +218,17 @@ static void QZ_SetPortAlphaOpaque () {
 
 @end
 
 @implementation SDL_QuartzView
 
+void QZ_UpdateRectsOnDrawRect(/*TODO: NSRect from drawRect*/);
+
+- (void)drawRect:(NSRect)dirtyRect
+{
+    QZ_UpdateRectsOnDrawRect();
+}
+
 - (void)resetCursorRects
 {
     SDL_Cursor *sdlc = SDL_GetCursor();
     if (sdlc != NULL && sdlc->wm_cursor != NULL) {
         [self addCursorRect: [self visibleRect] cursor: sdlc->wm_cursor->nscursor];