Having learnt a bit more: eliminates Metal attribute tags, switches to more natural expression of structs.

Also thereby eliminates the need for a forced alignas(4) on various structs.

OSBindings/Mac/Clock Signal/ScanTarget/ScanTarget.metal

@@ -12,31 +12,43 @@ using namespace metal;
 struct Uniforms {
 	// This is used to scale scan positions, i.e. it provides the range
 	// for mapping from scan-style integer positions into eye space.
-	int2 scale						[[attribute(0)]];
+	int2 scale;
 
 	// This provides the intended height of a scan, in eye-coordinate terms.
-	float lineWidth					[[attribute(1)]];
+	float lineWidth;
 
 	// Provides a scaling factor in order to preserve 4:3 central content.
-	float aspectRatioMultiplier		[[attribute(2)]];
+	float aspectRatioMultiplier;
 };
 
-// This is intended to match `Scan` as defined by the BufferingScanTarget.
+// This is intended to match the net effect of `Scan` as defined by the BufferingScanTarget.
-// Fields have been combined as necessary to make them all at least four
-// bytes in size, since that is the required attribute alignment in Swift.
 struct Scan {
-	uint32_t startPosition			[[attribute(0)]];
+	struct EndPoint {
-	uint32_t startOffsetAndAngle	[[attribute(1)]];
+		uint16_t position[2];
-	uint32_t startCycles			[[attribute(2)]];
+		uint16_t dataOffset;
+		uint16_t compositeAngle;
+		uint16_t cyclesSinceRetrace;
+	} endPoints[2];
 
-	uint32_t endPosition			[[attribute(3)]];
+	uint8_t compositeAmplitude;
-	uint32_t endOffsetAndAngle		[[attribute(4)]];
+	uint16_t dataY;
-	uint32_t endCycles				[[attribute(5)]];
+	uint16_t line;
-
-	uint32_t compositeAmplitude		[[attribute(6)]];
-	uint32_t dataYAndLine			[[attribute(7)]];
 };
 
+// This matches the BufferingScanTarget's `Line`.
+struct Line {
+	struct EndPoint {
+		uint16_t position[2];
+		uint16_t cyclesSinceRetrace;
+		uint16_t compositeAngle;
+	} endPoints[2];
+
+	uint16_t line;
+	uint8_t compositeAmplitude;
+};
+
+
+// This is an intermediate struct, which is TEMPORARY.
 struct ColouredVertex {
 	float4 position [[position]];
 };
@@ -48,21 +60,21 @@ vertex ColouredVertex scanVertexMain(	constant Uniforms &uniforms [[buffer(1)]],
 										constant Scan *scans [[buffer(0)]],
 										uint instanceID [[instance_id]],
 										uint vertexID [[vertex_id]]) {
-	// Unpack start and end vertices; little-endian numbers are assumed here.
+	// Get start and end vertices in regular float2 form.
 	const float2 start = float2(
-		float(scans[instanceID].startPosition & 0xffff) / float(uniforms.scale.x),
+		float(scans[instanceID].endPoints[0].position[0]) / float(uniforms.scale.x),
-		float(scans[instanceID].startPosition >> 16) / float(uniforms.scale.y)
+		float(scans[instanceID].endPoints[0].position[1]) / float(uniforms.scale.y)
 	);
 	const float2 end = float2(
-		float(scans[instanceID].endPosition & 0xffff) / float(uniforms.scale.x),
+		float(scans[instanceID].endPoints[1].position[0]) / float(uniforms.scale.x),
-		float(scans[instanceID].endPosition >> 16) / float(uniforms.scale.y)
+		float(scans[instanceID].endPoints[1].position[1]) / float(uniforms.scale.y)
 	);
 
 	// Calculate the tangent and normal.
 	const float2 tangent = (end - start);
 	const float2 normal = float2(-tangent.y, tangent.x) / length(tangent);
 
-	// Hence determine this quad's real shape.
+	// Hence determine this quad's real shape, using vertexID to pick a corner.
 	ColouredVertex output;
 	output.position = float4(
 		((start + (float(vertexID&2) * 0.5) * tangent + (float(vertexID&1) - 0.5) * normal * uniforms.lineWidth) * float2(2.0, -2.0) + float2(-1.0, 1.0)) * float2(uniforms.aspectRatioMultiplier, 1.0),
@@ -72,6 +84,6 @@ vertex ColouredVertex scanVertexMain(	constant Uniforms &uniforms [[buffer(1)]],
 	return output;
 }
 
-fragment float4 scanFragmentMain(ColouredVertex vert [[stage_in]]) {
+fragment half4 scanFragmentMain(ColouredVertex vert [[stage_in]]) {
-	return float4(1.0);
+	return half4(1.0);
 }

Outputs/ScanTarget.hpp

@@ -210,11 +210,9 @@ struct ScanTarget {
 
 		/*!
 			Defines a scan in terms of its two endpoints.
-
-			Is guaranteed to be a multiple of four bytes in size.
 		*/
-		struct alignas(4) Scan {
+		struct Scan {
-			struct alignas(4) EndPoint {
+			struct EndPoint {
 				/// Provide the coordinate of this endpoint. These are fixed point, purely fractional
 				/// numbers, relative to the scale provided in the Modals.
 				uint16_t x, y;

Outputs/ScanTargets/BufferingScanTarget.hpp

@@ -50,7 +50,7 @@ class BufferingScanTarget: public Outputs::Display::ScanTarget {
 
 		// Extends the definition of a Scan to include two extra fields,
 		// completing this scan's source data and destination locations.
-		struct alignas(4) Scan {
+		struct Scan {
 			Outputs::Display::ScanTarget::Scan scan;
 
 			/// Stores the y coordinate for this scan's data within the write area texture.
@@ -65,8 +65,8 @@ class BufferingScanTarget: public Outputs::Display::ScanTarget {
 		/// Defines the boundaries of a complete line of video — a 2d start and end location,
 		/// composite phase and amplitude (if relevant), the source line in the intermediate buffer
 		/// plus the start and end offsets of the area that is visible from the intermediate buffer.
-		struct alignas(4) Line {
+		struct Line {
-			struct alignas(4) EndPoint {
+			struct EndPoint {
 				uint16_t x, y;
 				uint16_t cycles_since_end_of_horizontal_retrace;
 				int16_t composite_angle;