internal/graphicsdriver/metal: Make FPS stable by 'presentsWithTransaction'

Closes #1196

internal/graphicsdriver/metal/ca/ca.go

@@ -147,6 +147,13 @@ func (ml MetalLayer) NextDrawable() (MetalDrawable, error) {
 	return MetalDrawable{md}, nil
 }
 
+// PresentsWithTransaction returns a Boolean value that determines whether the layer presents its content using a Core Animation transaction.
+//
+// Reference: https://developer.apple.com/documentation/quartzcore/cametallayer/1478157-presentswithtransaction
+func (ml MetalLayer) PresentsWithTransaction() bool {
+	return C.MetalLayer_PresentsWithTransaction(ml.metalLayer) != 0
+}
+
 // SetFramebufferOnly sets a Boolean value that determines whether the layer’s textures are used only for rendering.
 //
 // https://developer.apple.com/documentation/quartzcore/cametallayer/1478168-framebufferonly
@@ -175,3 +182,10 @@ func (md MetalDrawable) Drawable() unsafe.Pointer { return md.metalDrawable }
 func (md MetalDrawable) Texture() mtl.Texture {
 	return mtl.NewTexture(C.MetalDrawable_Texture(md.metalDrawable))
 }
+
+// Present presents the drawable onscreen as soon as possible.
+//
+// Reference: https://developer.apple.com/documentation/metal/mtldrawable/1470284-present.
+func (md MetalDrawable) Present() {
+	C.MetalDrawable_Present(md.metalDrawable)
+}

internal/graphicsdriver/metal/ca/ca.h

@@ -31,5 +31,7 @@ void MetalLayer_SetDisplaySyncEnabled(void *metalLayer,
 void MetalLayer_SetDrawableSize(void *metalLayer, double width, double height);
 void *MetalLayer_NextDrawable(void *metalLayer);
 void MetalLayer_SetFramebufferOnly(void *metalLayer, uint8_t framebufferOnly);
+uint8_t MetalLayer_PresentsWithTransaction(void *metalLayer);
 
 void *MetalDrawable_Texture(void *drawable);
+void MetalDrawable_Present(void *drawable);

internal/graphicsdriver/metal/ca/ca.m

@@ -85,6 +85,14 @@ void MetalLayer_SetDisplaySyncEnabled(void *metalLayer,
     [((CAMetalLayer *)metalLayer) setDisplaySyncEnabled:displaySyncEnabled];
   }
 #endif
+
+  // setting presentsWithTransaction YES makes the FPS stable (#1196). We're not
+  // sure why...
+  if (displaySyncEnabled) {
+    [((CAMetalLayer *)metalLayer) setPresentsWithTransaction:YES];
+  } else {
+    [((CAMetalLayer *)metalLayer) setPresentsWithTransaction:NO];
+  }
 }
 
 void MetalLayer_SetDrawableSize(void *metalLayer, double width, double height) {
@@ -99,6 +107,14 @@ void *MetalDrawable_Texture(void *metalDrawable) {
   return ((id<CAMetalDrawable>)metalDrawable).texture;
 }
 
+void MetalDrawable_Present(void *metalDrawable) {
+  [((id<CAMetalDrawable>)metalDrawable) present];
+}
+
 void MetalLayer_SetFramebufferOnly(void *metalLayer, uint8_t framebufferOnly) {
   [((CAMetalLayer *)metalLayer) setFramebufferOnly:framebufferOnly];
 }
+
+uint8_t MetalLayer_PresentsWithTransaction(void *metalLayer) {
+  return [((CAMetalLayer *)metalLayer) presentsWithTransaction];
+}

internal/graphicsdriver/metal/graphics.go

@@ -467,10 +467,14 @@ func (g *Graphics) flushIfNeeded(present bool) {
 	}
 	g.flushRenderCommandEncoderIfNeeded()
 
-	if present && g.screenDrawable != (ca.MetalDrawable{}) {
+	if !g.view.presentsWithTransaction() && present && g.screenDrawable != (ca.MetalDrawable{}) {
 		g.cb.PresentDrawable(g.screenDrawable)
 	}
 	g.cb.Commit()
+	if g.view.presentsWithTransaction() && present && g.screenDrawable != (ca.MetalDrawable{}) {
+		g.cb.WaitUntilScheduled()
+		g.screenDrawable.Present()
+	}
 
 	for _, t := range g.tmpTextures {
 		t.Release()

internal/graphicsdriver/metal/mtl/mtl.go

@@ -670,6 +670,13 @@ func (cb CommandBuffer) WaitUntilCompleted() {
 	C.CommandBuffer_WaitUntilCompleted(cb.commandBuffer)
 }
 
+// WaitUntilScheduled blocks execution of the current thread until the command buffer is scheduled.
+//
+// Reference: https://developer.apple.com/documentation/metal/mtlcommandbuffer/1443036-waituntilscheduled.
+func (cb CommandBuffer) WaitUntilScheduled() {
+	C.CommandBuffer_WaitUntilScheduled(cb.commandBuffer)
+}
+
 // MakeRenderCommandEncoder creates an encoder object that can
 // encode graphics rendering commands into this command buffer.
 //

internal/graphicsdriver/metal/mtl/mtl.h

@@ -153,6 +153,7 @@ uint8_t CommandBuffer_Status(void *commandBuffer);
 void CommandBuffer_PresentDrawable(void *commandBuffer, void *drawable);
 void CommandBuffer_Commit(void *commandBuffer);
 void CommandBuffer_WaitUntilCompleted(void *commandBuffer);
+void CommandBuffer_WaitUntilScheduled(void *commandBuffer);
 void *
 CommandBuffer_MakeRenderCommandEncoder(void *commandBuffer,
                                        struct RenderPassDescriptor descriptor);

internal/graphicsdriver/metal/mtl/mtl.m

@@ -188,6 +188,10 @@ void CommandBuffer_WaitUntilCompleted(void *commandBuffer) {
   [(id<MTLCommandBuffer>)commandBuffer waitUntilCompleted];
 }
 
+void CommandBuffer_WaitUntilScheduled(void *commandBuffer) {
+  [(id<MTLCommandBuffer>)commandBuffer waitUntilScheduled];
+}
+
 void *
 CommandBuffer_MakeRenderCommandEncoder(void *commandBuffer,
                                        struct RenderPassDescriptor descriptor) {

internal/graphicsdriver/metal/view.go

@@ -69,7 +69,10 @@ func (v *view) reset() error {
 	// MTLPixelFormatBGRA8Unorm_sRGB, MTLPixelFormatRGBA16Float, MTLPixelFormatBGRA10_XR, or
 	// MTLPixelFormatBGRA10_XR_sRGB.
 	v.ml.SetPixelFormat(mtl.PixelFormatBGRA8UNorm)
-	v.ml.SetMaximumDrawableCount(3)
+
+	// When presentsWithTransaction is YES and triple buffering is enabled, nextDrawing returns immediately once every two times.
+	// This makes FPS doubled. To avoid this, disable the triple buffering.
+	v.ml.SetMaximumDrawableCount(2)
 
 	// The vsync state might be reset. Set the state again (#1364).
 	v.ml.SetDisplaySyncEnabled(v.vsync)
@@ -86,3 +89,7 @@ func (v *view) nextDrawable() ca.MetalDrawable {
 	}
 	return d
 }
+
+func (v *view) presentsWithTransaction() bool {
+	return v.ml.PresentsWithTransaction()
+}