[macOS] Fix DelayFrameSwapping and optimise Vsync logic (#307)

* Support macOS 10.15 and 11
* Enable VSync option on macOS. Use "swapOnVSync" logic from other wsi
* Limit `mainui_rend_frame()` to 5 iterations max: 4 renders and the final swap

core/rend/gui.cpp

@@ -1432,9 +1432,7 @@ static void gui_display_settings()
 		    	}
 		    	OptionCheckbox("Widescreen Game Cheats", config::WidescreenGameHacks,
 		    			"Modify the game so that it displays in 16:9 anamorphic format and use horizontal screen stretching. Only some games are supported.");
-#ifndef __APPLE__
 		    	OptionCheckbox("VSync", config::VSync, "Synchronizes the frame rate with the screen refresh rate. Recommended");
-#endif
 		    	OptionCheckbox("Show FPS Counter", config::ShowFPS, "Show on-screen frame/sec counter");
 		    	OptionCheckbox("Show VMU In-game", config::FloatVMUs, "Show the VMU LCD screens while in-game");
 		    	OptionCheckbox("Rotate Screen 90°", config::Rotate90, "Rotate the screen 90° counterclockwise");

shell/apple/emulator-osx/emulator-osx/EmuGLView.swift

@@ -10,7 +10,8 @@ import Cocoa
 
 class EmuGLView: NSOpenGLView, NSWindowDelegate {
 
-    var backingRect:NSRect?
+    var backingRect: NSRect?
+    var swapOnVSync = emu_vsync_enabled()
     
     override var acceptsFirstResponder: Bool {
         return true;
@@ -20,19 +21,22 @@ class EmuGLView: NSOpenGLView, NSWindowDelegate {
         super.draw(dirtyRect)
         backingRect = convertToBacking(dirtyRect)
         
-        if emu_fast_forward() == false {
+        if swapOnVSync {
             draw()
         }
     }
     
     func draw() {
-        var sync: GLint = emu_fast_forward() ? 0 : 1
-        CGLSetParameter(openGLContext!.cglContextObj!, kCGLCPSwapInterval, &sync)
+        if swapOnVSync == (emu_fast_forward() || !emu_vsync_enabled()) {
+            swapOnVSync = (!emu_fast_forward() && emu_vsync_enabled())
+            var sync: GLint = swapOnVSync ? 1 : 0
+            CGLSetParameter(openGLContext!.cglContextObj!, kCGLCPSwapInterval, &sync)
+        }
         
         if let backingRect = backingRect {
             openGLContext!.makeCurrentContext()
-            if (emu_single_frame(Int32(backingRect.width), Int32(backingRect.height)) != 0) {
-                openGLContext!.flushBuffer()
+            if emu_single_frame(Int32(backingRect.width), Int32(backingRect.height)) {
+                openGLContext!.flushBuffer() //Swap for macOS
             }
         }
     }
@@ -80,11 +84,11 @@ class EmuGLView: NSOpenGLView, NSWindowDelegate {
 		if (!emu_renderer_enabled()) {
 			NSApplication.shared.terminate(self)
 		}
-        else if (emu_frame_pending()) {
-            if emu_fast_forward() {
-                self.draw()
-            } else {
+        else if emu_frame_pending() {
+            if swapOnVSync {
                 self.needsDisplay = true
+            } else {
+                self.draw()
             }
         }
     }

shell/apple/emulator-osx/emulator-osx/emulator-osx-Bridging-Header.h

@@ -19,7 +19,8 @@ void emu_dc_term();
 void emu_gui_open_settings();
 bool emu_renderer_enabled();
 bool emu_fast_forward();
-int emu_single_frame(int w, int h);
+bool emu_vsync_enabled();
+bool emu_single_frame(int w, int h);
 void emu_gles_init(int width, int height);
 int emu_reicast_init();
 void emu_key_input(UInt16 keyCode, bool pressed, UInt32 modifierFlags);

shell/apple/emulator-osx/emulator-osx/osx-main.mm

@@ -131,14 +131,27 @@ bool emu_fast_forward()
     return settings.input.fastForwardMode;
 }
 
-int emu_single_frame(int w, int h)
+bool emu_vsync_enabled()
 {
-    if (!emu_frame_pending())
-        return 0;
+    return config::VSync;
+}
 
+bool emu_single_frame(int w, int h)
+{
     screen_width = w;
     screen_height = h;
-    return (int)mainui_rend_frame();
+    
+    //For DelayFrameSwapping: use while loop to call multple mainui_rend_frame() until rend_swap_frame(u32 fb_r_sof1)
+    int counter = 0;
+    while (mainui_enabled && counter < 5)
+    {
+        counter++;
+        if (mainui_rend_frame())
+        {
+            return true;
+        }
+    }
+    return false;
 }
 
 void emu_gles_init(int width, int height)