Makes an attempt to have the emulator fill the actual GPU buffers.

Not that they're drawn from correctly yet. I might first take a run at a new quick-path output route for emulated RGB displays, that just seeks to use the scans directly. No intermediate buffers. Besides probably being a good feature, it'll be a good way to ramp further up with Metal.

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

@@ -1122,6 +1122,7 @@
 		4B4DC8271D2C2470003C5BF8 /* C1540.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = C1540.hpp; sourceTree = "<group>"; };
 		4B4DC8291D2C27A4003C5BF8 /* SerialBus.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = SerialBus.cpp; sourceTree = "<group>"; };
 		4B4DC82A1D2C27A4003C5BF8 /* SerialBus.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = SerialBus.hpp; sourceTree = "<group>"; };
+		4B4F2B7024DF99D4000DA6B0 /* CSScanTarget+CppScanTarget.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = "CSScanTarget+CppScanTarget.h"; sourceTree = "<group>"; };
 		4B50AF7F242817F40099BBD7 /* QuartzCore.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = QuartzCore.framework; path = System/Library/Frameworks/QuartzCore.framework; sourceTree = SDKROOT; };
 		4B51F70920A521D700AFA2C1 /* Source.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = Source.hpp; sourceTree = "<group>"; };
 		4B51F70A20A521D700AFA2C1 /* Observer.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = Observer.hpp; sourceTree = "<group>"; };
@@ -2071,6 +2072,7 @@
 				4B228CDA24DA41880077EF25 /* ScanTarget.metal */,
 				4B228CD424D773B30077EF25 /* CSScanTarget.mm */,
 				4B228CD624D773CA0077EF25 /* CSScanTarget.h */,
+				4B4F2B7024DF99D4000DA6B0 /* CSScanTarget+CppScanTarget.h */,
 			);
 			path = ScanTarget;
 			sourceTree = "<group>";

OSBindings/Mac/Clock Signal/Machine/CSMachine.mm

@@ -11,7 +11,7 @@
 
 #import "CSHighPrecisionTimer.h"
 #include "CSROMFetcher.hpp"
-#import "CSScanTarget.h"
+#import "CSScanTarget+CppScanTarget.h"
 
 #include "MediaTarget.hpp"
 #include "JoystickMachine.hpp"
@@ -353,14 +353,7 @@ struct ActivityObserver: public Activity::Observer {
 - (void)setView:(CSScanTargetView *)view aspectRatio:(float)aspectRatio {
 	_view = view;
 	_view.displayLinkDelegate = self;
-//	[view performWithGLContext:^{
+	_machine->scan_producer()->set_scan_target(_view.scanTarget.scanTarget);
-//		[self setupOutputWithAspectRatio:aspectRatio];
-//	} flushDrawable:NO];
-}
-
-- (void)setupOutputWithAspectRatio:(float)aspectRatio {
-//	_scanTarget = std::make_unique<Outputs::Display::OpenGL::ScanTarget>();
-//	_machine->scan_producer()->set_scan_target(_scanTarget.get());
 }
 
 - (void)updateViewForPixelSize:(CGSize)pixelSize {

OSBindings/Mac/Clock Signal/ScanTarget/CSScanTarget+CppScanTarget.h

@@ -0,0 +1,16 @@
+//
+//  CSScanTarget+C__ScanTarget.h
+//  Clock Signal
+//
+//  Created by Thomas Harte on 08/08/2020.
+//  Copyright © 2020 Thomas Harte. All rights reserved.
+//
+
+#import "CSScanTarget.h"
+#include "ScanTarget.hpp"
+
+@interface CSScanTarget (CppScanTarget)
+
+@property (nonatomic, readonly, nonnull) Outputs::Display::ScanTarget *scanTarget;
+
+@end

OSBindings/Mac/Clock Signal/ScanTarget/CSScanTarget.mm

@@ -20,9 +20,12 @@ struct Uniforms {
 };
 
 constexpr size_t NumBufferedScans = 2048;
+constexpr size_t NumBufferedLines = 2048;
 
 }
 
+using BufferingScanTarget = Outputs::Display::BufferingScanTarget;
+
 @implementation CSScanTarget {
 	id<MTLCommandQueue> _commandQueue;
 
@@ -32,10 +35,17 @@ constexpr size_t NumBufferedScans = 2048;
 
 	// Buffers.
 	id<MTLBuffer> _uniformsBuffer;
+
 	id<MTLBuffer> _scansBuffer;
+	id<MTLBuffer> _linesBuffer;
+	id<MTLBuffer> _writeAreaBuffer;
 
 	// Current uniforms.
 	Uniforms _uniforms;
+
+	// The scan target in C++-world terms and the non-GPU storage for it.
+	BufferingScanTarget _scanTarget;
+	BufferingScanTarget::LineMetadata _lineMetadataBuffer[NumBufferedLines];
 }
 
 - (nonnull instancetype)initWithView:(nonnull MTKView *)view {
@@ -43,7 +53,7 @@ constexpr size_t NumBufferedScans = 2048;
 	if(self) {
 		_commandQueue = [view.device newCommandQueue];
 
-		// Allocate space for uniforms.
+		// Allocate space for uniforms and FOR TEST PURPOSES set some.
 		_uniformsBuffer = [view.device newBufferWithLength:16 options:MTLResourceCPUCacheModeWriteCombined];
 		_uniforms.scale[0] = 1024;
 		_uniforms.scale[1] = 1024;
@@ -51,10 +61,23 @@ constexpr size_t NumBufferedScans = 2048;
 		_uniforms.aspectRatioMultiplier = 1.0f;
 		[self setUniforms];
 
-		// Allocate a large buffer for scans.
+		// Allocate buffers for scans and lines and for the write area texture.
 		_scansBuffer = [view.device
 			newBufferWithLength:sizeof(Outputs::Display::BufferingScanTarget::Scan)*NumBufferedScans
 			options:MTLResourceCPUCacheModeWriteCombined | MTLResourceStorageModeShared];
+		_linesBuffer = [view.device
+			newBufferWithLength:sizeof(Outputs::Display::BufferingScanTarget::Line)*NumBufferedLines
+			options:MTLResourceCPUCacheModeWriteCombined | MTLResourceStorageModeShared];
+		_writeAreaBuffer = [view.device
+			newBufferWithLength:BufferingScanTarget::WriteAreaWidth*BufferingScanTarget::WriteAreaHeight*4
+			options:MTLResourceCPUCacheModeWriteCombined | MTLResourceStorageModeShared];
+
+		// Install all that storage in the buffering scan target.
+		_scanTarget.set_write_area(reinterpret_cast<uint8_t *>(_writeAreaBuffer.contents));
+		_scanTarget.set_line_buffer(reinterpret_cast<BufferingScanTarget::Line *>(_linesBuffer.contents), _lineMetadataBuffer, NumBufferedLines);
+		_scanTarget.set_scan_buffer(reinterpret_cast<BufferingScanTarget::Scan *>(_scansBuffer.contents), NumBufferedScans);
+
+		// TEST ONLY: set some test data.
 		[self setTestScans];
 
 		// Generate TEST pipeline.
@@ -74,7 +97,7 @@ constexpr size_t NumBufferedScans = 2048;
 }
 
 - (void)setTestScans {
-	Outputs::Display::BufferingScanTarget::Scan scans[2];
+	BufferingScanTarget::Scan scans[2];
 	scans[0].scan.end_points[0].x = 0;
 	scans[0].scan.end_points[0].y = 0;
 	scans[0].scan.end_points[1].x = 1024;
@@ -129,4 +152,8 @@ constexpr size_t NumBufferedScans = 2048;
 	[commandBuffer commit];
 }
 
+-  (Outputs::Display::ScanTarget *)scanTarget {
+	return &_scanTarget;
+}
+
 @end

OSBindings/Mac/Clock Signal/Views/CSScanTargetView.h

@@ -11,6 +11,7 @@
 #import <MetalKit/MetalKit.h>
 
 @class CSScanTargetView;
+@class CSScanTarget;
 
 typedef NS_ENUM(NSInteger, CSScanTargetViewRedrawEvent) {
 	/// Indicates that AppKit requested a redraw for some reason (mostly likely, the window is being resized). So,
@@ -179,4 +180,9 @@ typedef NS_ENUM(NSInteger, CSScanTargetViewRedrawEvent) {
 */
 - (void)releaseMouse;
 
+/*!
+	@returns The CSScanTarget being used for this display.
+*/
+@property(nonatomic, readonly, nonnull) CSScanTarget *scanTarget;
+
 @end

OSBindings/Mac/Clock Signal/Views/CSScanTargetView.m

@@ -164,6 +164,10 @@ static CVReturn DisplayLinkCallback(__unused CVDisplayLinkRef displayLink, const
 	CVDisplayLinkRelease(_displayLink);
 }
 
+- (CSScanTarget *)scanTarget {
+	return _scanTarget;
+}
+
 - (CGSize)backingSize {
 	@synchronized(self) {
 		return _backingSize;