Factors out the stuff of deferred action interleaving, as I suspect it'll come in handy.

ClockReceiver/ClockDeferrer.hpp

@@ -0,0 +1,84 @@
+//
+//  ClockDeferrer.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 23/08/2018.
+//  Copyright © 2018 Thomas Harte. All rights reserved.
+//
+
+#ifndef ClockDeferrer_h
+#define ClockDeferrer_h
+
+#include <vector>
+
+/*!
+	A ClockDeferrer maintains a list of ordered actions and the times at which
+	they should happen, and divides a total execution period up into the portions
+	that occur between those actions, triggering each action when it is reached.
+
+	@c Class should be a class that implements @c advance(TimeUnit), to advance
+	that amount of time.
+*/
+template <typename TimeUnit> class ClockDeferrer {
+	public:
+		/// Constructs a ClockDeferrer that will call target.advance in between deferred actions.
+		ClockDeferrer(std::function<void(TimeUnit)> &&target) : target_(std::move(target)) {}
+
+		/*!
+			Schedules @c action to occur in @c delay units of time.
+
+			Actions must be scheduled in the order they will occur. It is undefined behaviour
+			to schedule them out of order.
+		*/
+		void defer(TimeUnit delay, const std::function<void(void)> &action) {
+			pending_actions_.emplace_back(delay, action);
+		}
+
+		/*!
+			Runs for @c length units of time.
+
+			The target's @c advance will be called with one or more periods that add up to @c length;
+			any scheduled actions will be called between periods.
+		*/
+		void run_for(TimeUnit length) {
+			// If there are no pending actions, just run for the entire length.
+			// This should be the normal branch.
+			if(pending_actions_.empty()) {
+				target_(length);
+				return;
+			}
+
+			// Divide the time to run according to the pending actions.
+			while(length > TimeUnit(0)) {
+				TimeUnit next_period = pending_actions_.empty() ? length : std::min(length, pending_actions_[0].delay);
+				target_(next_period);
+				length -= next_period;
+
+				off_t performances = 0;
+				for(auto &action: pending_actions_) {
+					action.delay -= next_period;
+					if(!action.delay) {
+						action.action();
+						++performances;
+					}
+				}
+				if(performances) {
+					pending_actions_.erase(pending_actions_.begin(), pending_actions_.begin() + performances);
+				}
+			}
+		}
+
+	private:
+		std::function<void(TimeUnit)> target_;
+
+		// The list of deferred actions.
+		struct DeferredAction {
+			TimeUnit delay;
+			std::function<void(void)> action;
+
+			DeferredAction(TimeUnit delay, const std::function<void(void)> &action) : delay(delay), action(std::move(action)) {}
+		};
+		std::vector<DeferredAction> pending_actions_;
+};
+
+#endif /* ClockDeferrer_h */

Machines/AppleII/Video.cpp

@@ -10,9 +10,10 @@
 
 using namespace AppleII::Video;
 
-VideoBase::VideoBase(bool is_iie) :
+VideoBase::VideoBase(bool is_iie, std::function<void(Cycles)> &&target) :
 	crt_(new Outputs::CRT::CRT(910, 1, Outputs::CRT::DisplayType::NTSC60, 1)),
-	is_iie_(is_iie) {
+	is_iie_(is_iie),
+	deferrer_(std::move(target)) {
 
 	// Set a composite sampling function that assumes one byte per pixel input, and
 	// accepts any non-zero value as being fully on, zero being fully off.
@@ -37,7 +38,7 @@ Outputs::CRT::CRT *VideoBase::get_crt() {
 */
 void VideoBase::set_alternative_character_set(bool alternative_character_set) {
 	set_alternative_character_set_ = alternative_character_set;
-	defer(2, [=] {
+	deferrer_.defer(Cycles(2), [=] {
 		alternative_character_set_ = alternative_character_set;
 	});
 }
@@ -48,7 +49,7 @@ bool VideoBase::get_alternative_character_set() {
 
 void VideoBase::set_80_columns(bool columns_80) {
 	set_columns_80_ = columns_80;
-	defer(2, [=] {
+	deferrer_.defer(Cycles(2), [=] {
 		columns_80_ = columns_80;
 	});
 }
@@ -75,7 +76,7 @@ bool VideoBase::get_page2() {
 
 void VideoBase::set_text(bool text) {
 	set_text_ = text;
-	defer(2, [=] {
+	deferrer_.defer(Cycles(2), [=] {
 		text_ = text;
 	});
 }
@@ -86,7 +87,7 @@ bool VideoBase::get_text() {
 
 void VideoBase::set_mixed(bool mixed) {
 	set_mixed_ = mixed;
-	defer(2, [=] {
+	deferrer_.defer(Cycles(2), [=] {
 		mixed_ = mixed;
 	});
 }
@@ -97,7 +98,7 @@ bool VideoBase::get_mixed() {
 
 void VideoBase::set_high_resolution(bool high_resolution) {
 	set_high_resolution_ = high_resolution;
-	defer(2, [=] {
+	deferrer_.defer(Cycles(2), [=] {
 		high_resolution_ = high_resolution;
 	});
 }
@@ -108,7 +109,7 @@ bool VideoBase::get_high_resolution() {
 
 void VideoBase::set_double_high_resolution(bool double_high_resolution) {
 	set_double_high_resolution_ = double_high_resolution;
-	defer(2, [=] {
+	deferrer_.defer(Cycles(2), [=] {
 		double_high_resolution_ = double_high_resolution;
 	});
 }
@@ -301,7 +302,3 @@ void VideoBase::output_double_high_resolution(uint8_t *target, uint8_t *source,
 		target += 14;
 	}
 }
-
-void VideoBase::defer(int delay, const std::function<void(void)> &action) {
-	pending_actions_.emplace_back(delay, action);
-}

Machines/AppleII/Video.hpp

@@ -11,6 +11,7 @@
 
 #include "../../Outputs/CRT/CRT.hpp"
 #include "../../ClockReceiver/ClockReceiver.hpp"
+#include "../../ClockReceiver/ClockDeferrer.hpp"
 
 #include <array>
 #include <vector>
@@ -33,7 +34,7 @@ class BusHandler {
 
 class VideoBase {
 	public:
-		VideoBase(bool is_iie);
+		VideoBase(bool is_iie, std::function<void(Cycles)> &&target);
 
 		/// @returns The CRT this video feed is feeding.
 		Outputs::CRT::CRT *get_crt();
@@ -224,58 +225,22 @@ class VideoBase {
 		*/
 		void output_double_high_resolution(uint8_t *target, uint8_t *source, uint8_t *auxiliary_source, size_t length) const;
 
-		/// Schedule @c action to occur in @c delay cycles.
-		void defer(int delay, const std::function<void(void)> &action);
-
-		// The list of deferred actions.
-		struct DeferredAction {
-			int delay;
-			std::function<void(void)> action;
-
-			DeferredAction(int delay, const std::function<void(void)> &action) : delay(delay), action(std::move(action)) {}
-		};
-		std::vector<DeferredAction> pending_actions_;
+		// Maintain a ClockDeferrer for delayed mode switches.
+		ClockDeferrer<Cycles> deferrer_;
 };
 
 template <class BusHandler, bool is_iie> class Video: public VideoBase {
 	public:
 		/// Constructs an instance of the video feed; a CRT is also created.
 		Video(BusHandler &bus_handler) :
-			VideoBase(is_iie),
+			VideoBase(is_iie, [=] (Cycles cycles) { advance(cycles); }),
 			bus_handler_(bus_handler) {}
 
 		/*!
-			Advances time by @c cycles; expects to be fed by the CPU clock.
-			Implicitly adds an extra half a colour clock at the end of every
-			line.
+			Runs video for @c cycles.
 		*/
 		void run_for(Cycles cycles) {
-			// If there are no pending actions, just run for the entire length.
-			// This should be the normal branch.
-			if(pending_actions_.empty()) {
-				advance(cycles.as_int());
-				return;
-			}
-
-			// Divide the time to run according to the pending actions.
-			int cycles_remaining = cycles.as_int();
-			while(cycles_remaining) {
-				int next_period = pending_actions_.empty() ? cycles_remaining : std::min(cycles_remaining, pending_actions_[0].delay);
-				advance(next_period);
-				cycles_remaining -= next_period;
-
-				off_t performances = 0;
-				for(auto &action: pending_actions_) {
-					action.delay -= next_period;
-					if(!action.delay) {
-						action.action();
-						++performances;
-					}
-				}
-				if(performances) {
-					pending_actions_.erase(pending_actions_.begin(), pending_actions_.begin() + performances);
-				}
-			}
+			deferrer_.run_for(cycles);
 		}
 
 		/*!
@@ -336,6 +301,11 @@ template <class BusHandler, bool is_iie> class Video: public VideoBase {
 		}
 
 	private:
+		/*!
+			Advances time by @c cycles; expects to be fed by the CPU clock.
+			Implicitly adds an extra half a colour clock at the end of
+			line.
+		*/
 		void advance(Cycles cycles) {
 			/*
 				Addressing scheme used throughout is that column 0 is the first column with pixels in it;

OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj

@@ -1007,6 +1007,7 @@
 		4B894516201967B4007DE474 /* StaticAnalyser.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = StaticAnalyser.cpp; sourceTree = "<group>"; };
 		4B894517201967B4007DE474 /* StaticAnalyser.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = StaticAnalyser.cpp; sourceTree = "<group>"; };
 		4B894540201967D6007DE474 /* Machines.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = Machines.hpp; sourceTree = "<group>"; };
+		4B8A7E85212F988200F2BBC6 /* ClockDeferrer.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = ClockDeferrer.hpp; sourceTree = "<group>"; };
 		4B8D287E1F77207100645199 /* TrackSerialiser.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = TrackSerialiser.hpp; sourceTree = "<group>"; };
 		4B8E4ECD1DCE483D003716C3 /* KeyboardMachine.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = KeyboardMachine.hpp; sourceTree = "<group>"; };
 		4B8EF6071FE5AF830076CCDD /* LowpassSpeaker.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = LowpassSpeaker.hpp; sourceTree = "<group>"; };
@@ -3149,6 +3150,7 @@
 				4BB06B211F316A3F00600C7A /* ForceInline.hpp */,
 				4BB146C61F49D7D700253439 /* ClockingHintSource.hpp */,
 				4B449C942063389900A095C8 /* TimeTypes.hpp */,
+				4B8A7E85212F988200F2BBC6 /* ClockDeferrer.hpp */,
 			);
 			name = ClockReceiver;
 			path = ../../ClockReceiver;