Reland "Minimal iOS app: Perform present subsequent to flush"

This is a reland of 4e385e2

Original change's description:
> Minimal iOS app: Perform present subsequent to flush
> 
> Currently the backbuffer present is not on the same MTLCommandQueue
> as the flush from Skia, which probably means that it's happening
> concurrently. This can overwhelm the GPU. This CL submits the present
> to the same queue as the flush.
> 
> Change-Id: Ibaf805553931c9dc46368b362a2391425ae3e60e
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/248557
> Reviewed-by: Hal Canary <halcanary@skia.org>
> Commit-Queue: Jim Van Verth <jvanverth@google.com>

Change-Id: I118047630b8936838d5da8ef4307ad5c5e8d2ade
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/248562
Reviewed-by: Hal Canary <halcanary@skia.org>
Commit-Queue: Jim Van Verth <jvanverth@google.com>

Author: jvanverth

experimental/minimal_ios_mtl_skia_app/main.mm

@@ -44,6 +44,7 @@ static void draw_example(SkSurface* surface, const SkPaint& paint, double rotati
 
 @interface AppViewDelegate : NSObject <MTKViewDelegate>
 @property (assign, nonatomic) GrContext* grContext;  // non-owning pointer.
+@property (assign, nonatomic) id<MTLCommandQueue> metalQueue;
 @end
 
 @implementation AppViewDelegate {
@@ -70,7 +71,10 @@ - (void)drawInMTKView:(nonnull MTKView *)view {
     // Must flush *and* present for this to work!
     surface->flush();
     surface = nullptr;
-    [[view currentDrawable] present];
+
+    id<MTLCommandBuffer> commandBuffer = [[self metalQueue] commandBuffer];
+    [commandBuffer presentDrawable:[view currentDrawable]];
+    [commandBuffer commit];
 }
 
 - (void)mtkView:(nonnull MTKView *)view drawableSizeWillChange:(CGSize)size {
@@ -82,6 +86,7 @@ - (void)mtkView:(nonnull MTKView *)view drawableSizeWillChange:(CGSize)size {
 
 @interface AppViewController : UIViewController
 @property (strong, nonatomic) id<MTLDevice> metalDevice;
+@property (strong, nonatomic) id<MTLCommandQueue> metalQueue;
 @end
 
 @implementation AppViewController {
@@ -96,8 +101,9 @@ - (void)viewDidLoad {
     [super viewDidLoad];
     if (!fGrContext) {
         [self setMetalDevice:MTLCreateSystemDefaultDevice()];
+        [self setMetalQueue:[[self metalDevice] newCommandQueue]];
         GrContextOptions grContextOptions;  // set different options here.
-        fGrContext = SkMetalDeviceToGrContext([self metalDevice], grContextOptions);
+        fGrContext = SkMetalDeviceToGrContext([self metalDevice], [self metalQueue], grContextOptions);
     }
     if (![self view] || ![self metalDevice]) {
         NSLog(@"Metal is not supported on this device");
@@ -110,6 +116,7 @@ - (void)viewDidLoad {
     SkMtkViewConfigForSkia(mtkView);
     AppViewDelegate* viewDelegate = [[AppViewDelegate alloc] init];
     [viewDelegate setGrContext:fGrContext.get()];
+    [viewDelegate setMetalQueue:[self metalQueue]];
     [viewDelegate mtkView:mtkView drawableSizeWillChange:[mtkView bounds].size];
     [mtkView setDelegate:viewDelegate];
 }

experimental/skottie_ios/SkMetalViewBridge.h

@@ -12,7 +12,7 @@ template <typename T> class sk_sp;
 
 sk_sp<SkSurface> SkMtkViewToSurface(MTKView*, GrContext*);
 
-sk_sp<GrContext> SkMetalDeviceToGrContext(id<MTLDevice>, const GrContextOptions&);
+sk_sp<GrContext> SkMetalDeviceToGrContext(id<MTLDevice>, id<MTLCommandQueue>, const GrContextOptions&);
 
 void SkMtkViewConfigForSkia(MTKView*);
 

experimental/skottie_ios/SkMetalViewBridge.mm

@@ -41,9 +41,8 @@
     }
 }
 
-sk_sp<GrContext> SkMetalDeviceToGrContext(id<MTLDevice> device, const GrContextOptions& opts) {
-    return GrContext::MakeMetal((void*)device,
-                                (void*)[device newCommandQueue], opts);
+sk_sp<GrContext> SkMetalDeviceToGrContext(id<MTLDevice> device, id<MTLCommandQueue> queue, const GrContextOptions& opts) {
+    return GrContext::MakeMetal((void*)device, (void*)queue, opts);
 }
 
 void SkMtkViewConfigForSkia(MTKView* mtkView) {

experimental/skottie_ios/SkottieMtkView.h

@@ -14,6 +14,9 @@ class GrContext;
 // e.g.: use SkMetalDeviceToGrContext().
 @property (assign) GrContext* grContext;  // non-owning pointer.
 
+// Must be set to a valid MTLCommandQueue. Will be used to present.
+@property (assign) id<MTLCommandQueue> queue;  // non-owning pointer.
+
 // When set, pauses at end of loop.
 @property (assign) BOOL stopAtEnd;
 

experimental/skottie_ios/SkottieMtkView.mm

@@ -63,7 +63,10 @@ - (void)drawRect:(CGRect)rect {
     fAnimation->render(canvas);
     surface->flush();
     surface = nullptr;
-    [[self currentDrawable] present];
+
+    id<MTLCommandBuffer> commandBuffer = [[self queue] commandBuffer];
+    [commandBuffer presentDrawable:[self currentDrawable]];
+    [commandBuffer commit];
 }
 
 - (BOOL)loadAnimation:(NSData*) data {

experimental/skottie_ios/main.mm

@@ -13,6 +13,7 @@
 
 static UIStackView* make_skottie_stack(CGFloat width,
                                        id<MTLDevice> metalDevice,
+                                       id<MTLCommandQueue> metalQueue,
                                        GrContext* grContext) {
     UIStackView* stack = [[UIStackView alloc] init];
     [stack setAxis:UILayoutConstraintAxisVertical];
@@ -35,6 +36,7 @@
             continue;
         }
         [skottieView setDevice:metalDevice];
+        [skottieView setQueue:metalQueue];
         [skottieView setGrContext:grContext];
         SkMtkViewConfigForSkia(skottieView);
         CGSize animSize = [skottieView size];
@@ -52,6 +54,7 @@
 
 @interface AppViewController : UIViewController
     @property (strong) id<MTLDevice> metalDevice;
+    @property (strong) id<MTLCommandQueue> metalQueue;
     @property (strong) UIStackView* stackView;
 @end
 
@@ -76,12 +79,14 @@ - (void)viewDidLoad {
             NSLog(@"Metal is not supported on this device");
             return;
         }
+        [self setMetalQueue:[[self metalDevice] newCommandQueue]];
         GrContextOptions grContextOptions;  // set different options here.
-        fGrContext = SkMetalDeviceToGrContext([self metalDevice], grContextOptions);
+        fGrContext = SkMetalDeviceToGrContext([self metalDevice], [self metalQueue],
+                                              grContextOptions);
     }
 
     [self setStackView:make_skottie_stack([[UIScreen mainScreen] bounds].size.width,
-                                          [self metalDevice], fGrContext.get())];
+                                          [self metalDevice], [self metalQueue], fGrContext.get())];
 
     CGFloat statusBarHeight = [[UIApplication sharedApplication] statusBarFrame].size.height;
     CGSize mainScreenSize = [[UIScreen mainScreen] bounds].size;