Adds a use-square-pixels option for the Apple II.

Machines/Apple/AppleII/AppleII.cpp

@@ -787,12 +787,14 @@ template <Analyser::Static::AppleII::Target::Model model> class ConcreteMachine:
 		std::unique_ptr<Reflection::Struct> get_options() final {
 			auto options = std::make_unique<Options>(Configurable::OptionsType::UserFriendly);
 			options->output = get_video_signal_configurable();
+			options->use_square_pixels = video_.get_use_square_pixels();
 			return options;
 		}
 
 		void set_options(const std::unique_ptr<Reflection::Struct> &str) {
 			const auto options = dynamic_cast<Options *>(str.get());
 			set_video_signal_configurable(options->output);
+			video_.set_use_square_pixels(options->use_square_pixels);
 		}
 
 		// MARK: MediaTarget

Machines/Apple/AppleII/AppleII.hpp

@@ -30,10 +30,16 @@ class Machine {
 		class Options: public Reflection::StructImpl<Options>, public Configurable::DisplayOption<Options> {
 			friend Configurable::DisplayOption<Options>;
 			public:
-				Options(Configurable::OptionsType) : Configurable::DisplayOption<Options>(Configurable::Display::CompositeColour)  {
+				bool use_square_pixels = false;
+
+				Options(Configurable::OptionsType) : Configurable::DisplayOption<Options>(Configurable::Display::CompositeColour) {
 					if(needs_declare()) {
 						declare_display_option();
 						limit_enum(&output, Configurable::Display::CompositeMonochrome, Configurable::Display::CompositeColour, -1);
+
+						if(needs_declare()) {
+							DeclareField(use_square_pixels);
+						}
 					}
 				}
 		};

Machines/Apple/AppleII/Video.cpp

@@ -26,6 +26,30 @@ VideoBase::VideoBase(bool is_iie, std::function<void(Cycles)> &&target) :
 //	crt_.set_immediate_default_phase(0.5f);
 }
 
+void VideoBase::set_use_square_pixels(bool use_square_pixels) {
+	use_square_pixels_ = use_square_pixels;
+
+	if(use_square_pixels) {
+		// From what I can make out, many contemporary Apple II monitors were
+		// calibrated slightly to stretch the Apple II's display slightly wider
+		// than it should be per the NTSC standards, for approximately square
+		// pixels. This reproduces that.
+
+		// 243 lines and 52µs are visible.
+		// i.e. to be square, 1 pixel should be: (1/243 * 52) * (3/4) = 156/972 = 39/243 µs
+		// On an Apple II each pixel is actually 1/7µs.
+		// Therefore the adjusted aspect ratio should be (4/3) * (39/243)/(1/7) = (4/3) * 273/243 = 1092/729 = 343/243 ~= 1.412
+		crt_.set_aspect_ratio(343.0f / 243.0f);
+	} else {
+		// Standard NTSC aspect ratio.
+		crt_.set_aspect_ratio(4.0f / 3.0f);
+	}
+}
+bool VideoBase::get_use_square_pixels() {
+	return use_square_pixels_;
+}
+
+
 void VideoBase::set_scan_target(Outputs::Display::ScanTarget *scan_target) {
 	crt_.set_scan_target(scan_target);
 }

Machines/Apple/AppleII/Video.hpp

@@ -51,8 +51,14 @@ class VideoBase: public VideoSwitches<Cycles> {
 		/// Gets the type of output.
 		Outputs::Display::DisplayType get_display_type() const;
 
+		/// Sets whether the current CRT should be recalibrated away from normative NTSC
+		/// to produce square pixels in 40-column text mode.
+		void set_use_square_pixels(bool);
+		bool get_use_square_pixels();
+
 	protected:
 		Outputs::CRT::CRT crt_;
+		bool use_square_pixels_ = false;
 
 		// State affecting output video stream generation.
 		uint8_t *pixel_pointer_ = nullptr;